UBC_1979_A7 D38.pdf - cIRcle - University of British Columbia

REFRACTORIES

IN VACUUM I N D U C T I O N

MELTING

by

Eng.

A n d r e L u i z V. da C o s t a e S i l v a M e t . , I n s t i t u t o M i l i t a r de E n g e n h a r i a , B r a s i l , 1 9 7 6

A T H E S I S S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF T H E R E Q U I R E M E N T S FOR THE D E G R E E OF M A S T E R OF A P P L I E D S C I E N C E

in THE F A C U L T Y OF G R A D U A T E S T U D I E S Department of M e t a l l u r g i c a l Engineering

We a c c e p t t h i s t h e s i s a s c o n f o r m i n g to t h e r e q u i r e d s t a n d a r d

T H E U N I V E R S I T Y OF B R I T I S H March,

COLUMBIA

1979

© A n d r e * L u i z V. da C o s t a e S i l v a , 1 9 7 9

In p r e s e n t i n g

this thesis i n p a r t i a l f u l f i l m e n t o f the requirements f o r

an advanced d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree that permission

f o r extensive copying o f t h i s t h e s i s

f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s .

I t i s understood that copying o r p u b l i c a t i o n

of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my written

permission.

Department

nf

Metallurgical

Engineering

The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5

D

a

t

e

March 20,

1979

\

ABSTRACT The

l i t e r a t u r e i n Vacuum I n d u c t i o n

reviewed, with

especial

refractory-metal

lining

superalloy

Since

i t was

with

attack

in large on

j o i n t s , t e s t s were p e r f o r m e d to c h a r a c t e r i z e

the

was

s h o w n t o be

to metal a t t a c k . diffusion

of the

less stable oxides

in the c o r r o s i o n

process.

high

i n t e r a c t i o n b e t w e e n o x y g e n and

may

be

In t h e c a s e

(SiO^,

the

content

as f l u x e s was

of the

In o r d e r

attempted.

properties

To v e r i f y t h e mechanisms observed industrial

of s t e e l s ,

of s u p e r a l l o y s ,

the e l e m e n t s p r e s e n t

The

the

fluorides

performed

of

t e s t s , samples

Vacuum F u r n a c e s were e x a m i n e d .

I t was

of very

and

concerned.

p r o p o s e d i n the

ii

of

a

adherence to b r i c k s

v a l i d i t y (on a l a r g e s c a l e )

and

the

dissolution

use

c e m e n t s so p r o d u c e d

to a t t a c k ,

were

of

the

in

to produce cements with

l o w - s t a b i l i t y oxides,

w e l l , as f a r a s r e s i s t a n c e technological

resistance

rate c o n t r o l l i n g

oxygen a c t i v i t y in the m e l t , hence e n h a n c i n g the

small

P^O^,...)

c a u s e s an e x t r e m e d e p r e s s i o n

refractory oxides.

and

standpoint.

t h a t i n the case

step

all

cement

f o r the c e m e n t s low

It i s suggested

the a l l o y ( T i , A l , Cr)

furnaces

1

the main reason

that

this attack

d e t e r m i n e the most s u i t a b l e cements from t h i s presence of l o w - s t a b i l i t y oxides

and

determined

vacuum m e l t i n g

f a i l u r e s are a s s o c i a t e d

The

is briefly

e m p h a s i s on r e f r a c t o r y p r a c t i c e s

interactions.

i n b o t h s t e e l and

Melting

the from

concluded

t h a t t h e p r o c e s s e s . o c c u r r i n g i n a 1 a r g e f u r n a c e c a n be i z e d based on t h e n e e d

on t h e t e s t o b s e r v a t i o n s . f o r improved

rational-

A l s o c o m m e n t s w e r e made

pouring f a c i l i t i e s ,

i f the

products

o f t h e m e t a l - r e f r a c t o r y i n t e r a c t i o n a r e t o be k e p t o u t o f final

material produced.

This i s because

i n the

present

s t a t e o f the r e f r a c t o r y t e c h n o l o g y and p r a c t i c e , t h e s e actions

cannot

be

avoided.

the

inter-

T A B L E OF C O N T E N T S Page Abstract Table

i i

of Contents

List

of Tables

List

of Figures

iv vi vii

Acknowledgements

'

x

CHAPTER 1. I N T R O D U C T I O N

1

1.1 I n t r o d u c t i on

1

1.2 L i t e r a t u r e S u r v e y 1.2.1 Meta1 - R e f r a c t o r y Interactions Under Vacuum 1. 2 . 1 . 1 V a p o r i z a t i on 1.2.1.2 D i s s o l u t i o n o f R e f r a c t o r i e s 1.2.1.3 R e a c t i o n w i t h A l l o y i n g E l e m e n t s 1.2.1.3.1 Carbon 1.2.1.3.2 O t h e r A l l o y i n g E l e m e n t s 1.2.1.4 E f f e c t o f M i n o r Components 1.2.1.5 K i n e t i c A s p e c t s 1.2.2 R e f r a c t o r y P r a c t i c e i n V I M 1.2.3 O t h e r R e a c t i o n s W i t h t h e L i n i n g

4

10 12 14 20

1.3 O b j e c t i v e s

24

o f the Research Project

4 4 4 5

2. E X P E R I M E N T A L

25

3. R E S U L T S

29

3.1 T e s t s U s i n g A I S I 1 0 9 5 S t e e l 3.1.1 M u l l i t e B a s e d Cement 3.1.2 C e m e n t s W i t h 1 0 % S i l i c a iv

29 29 31

Page 3.1.3 3.1.4 3.1.5 3.1.6 3.2

Cements Produced Using F l u o r i d e s Low S i l i c a P h o s p h a t e B o n d e d C e m e n t S i l i c a C o n t a i n i n g Phosphate Bonded Cement Summary o f S t e e l T e s t s

Tests Using

4. O B S E R V A T I O N OF

X-750 S u p e r a l l o y

42

INDUSTRIAL SAMPLES

50

4.1 4.2

S l a g From D e s u l p h u r i z a t i o n T r e a t m e n t Magnel B r i c k 4.2.1 M a c r o s c o p i c O b s e r v a t i o n 4.2.2 M i c r o s c o p i c O b s e r v a t i o n 4.3 I n c l u s i o n s i n N i - B a s e d S u p e r a l l o y 4.4 P i e c e o f Rammed L i n i n g 4.4.1 M a c r o s c o p i c O b s e r v a t i o n 4.4.2

Microscopic

5. C O N C L U S I O N S AND

32 36 38 40

50 52 52 52 56 58 58

Observation

58

RECOMMENDATIONS

61

BIBLIOGRAPHY

67

v

L I S T OF

TABLES Page

1. 2. 3.

S o l u b i l i t y product of various oxides in Iron and N i c k e l

121

P r e s s u r e s o f CO i n e q u i l i b r i u m w i t h d i f f e r e n t o x i d e s and s t e e l melts

121

Nominal composition

o f some

Vacuum

Melted Superalloys

122

4.

Refractory Practices

123

5.

Composition

of metals

6.

Composition

of Refractories tested

7.

O x y g e n c o n t e n t o f X - 7 5 0 a f t e r 15 m i n . h o l d i n g time i n d i f f e r e n t c r u c i b l e s

used

vi

i n the t e s t s

129 130 13:1

L I S T OF F I G U R E S 1.

Theoretical

2.

Deoxidation curves

3.

Dimensions

4.

Different wetting behaviours

77

5.

Experimental Apparatus

78

6.

V a r i a t i o n i n carbon c o n t e n t o f AISI melted i n Tasil-X crucibles

7.

Interface

8. 9. 10.

deoxidation

Page 74

diagram

75

o f the crucibles

AISI

used i n the t e s t s

1095 s t e e l 79

1095/Tasil-X

80

Microstructure

of Taylor

81

Interface

1 0 9 5 / A l u n d u m 1162

AISI

Typical microstructure A 1 0 and CaF (CAF) 2

3

320

82

o f a c e m e n t made

from 83

2

11.

Adherence test.

12.

V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n CAF c r u c i b l e s

1095 s t e e l

V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n Alundum 1139 c r u c i b l e s

1095 s t e e l

13. 14.

Interface

Typical microstructure A l 0 a n d MgF,, ( S P 2 ) 2

15.

76

Magnel/CAF

84 85 86

o f a c e m e n t made

from 87

3

V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n SP2 c r u c i b l e s

16.

Adherence t e s t .

17.

V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n T a y l o r 341 c r u c i b l e s AISI

Interface

1095 s t e e l 88

Magnel/SP2.

89

1095 s t e e l 90

18.

Interface

1 0 9 5 / T a y l o r 341

91

19.

V a r i a t i o n i n c a r b o n c o n t e n t o f AISI 1095 s t e e l m e l t e d i n C o r a l b o n d and T a s i l - X c r u c i b l e s as a f u n c t i o n o f th vii

92

Page 20.

Interface

AISI

1095/Cora1 bond

21.

Detail of altered Coralbond

22.

Alumina

i n c l u s i o n s from

Interface

AISI

93 94

Coralbond.

1095/Coralbond

23.

Equilibrium

24.

Interface

X-750/Magnel

25.

Interface

X-750/Magnel , metal

26.

Deoxidation

27. 28.

D e n s e l a y e r f o r m e d a t i n t e r f a c e X - 7 5 0 / T a y l o r 341 M i c r o s t r u c t u r e of s l a g from d e s u l p h u r i z a t i o n treatment

101

Microstructure treatment

102

29.

A1 0

95

2

3

= 2A_1 + 30 i n N i c k e l

equilibria

97

of s l a g from

Used Magnel

31.

Cross section of working Magnel b r i c k

33.

34.

98 99

Metal penetration Ca1cium-Aluminate and Z i r c o n i u m

103 face

of 104 brick 105

i n Magnel b r i c k . containing Titanium

Detail of a periclase grain

' in

brick

107

P e r i c l a s e g r a i n i n used Magnel

36.

C a l c i u m - A l u m i n a t e s on t h e w o r k i n g

brick

108

face

of Magnel l a y e r on t h e w o r k i n g

106

unused

35.

109

37.

Spinel

38.

Macroinc1 usions in p a r t i a l l y forged Ni-base superalloy Microstructure of Calcium-Aluminate i n c l u s i o n i n F i g . 38 vi i i

39.

100

desulphurization

brick

Metal p e n e t r a t i o n i n Magnel via Ca1cium-Aluminates

Magnel

removed

i n a N i - 1 % A1 a l l o y

30.

32.

96

f a c e o f Magnel

110 111 112

Page 40.

Microstructure partially

of spinel inclusion in

forged Ni-base alloy

41.

Piece

42.

Typical microstructure

113

o f u s e d rammed l i n i n g o f t h e rammed

114 lining,

60mm f r o m t h e w o r k i n g f a c e

115

43.

Cross-section

116

44.

Inclusions

45.

A l t e r e d r a m m e d l i n i n g 5mm f r o m t h e w o r k i n g face U n a l t e r e d MgO g r a i n c l o s e t o t h e w o r k i n g f a c e o f t h e rammed l i n i n g

46.

of working

f a c e o f rammed l i n i n g

f r o m rammed l i n i n g

ix

117 118 119

ACKNOWLEDGEMENTS The

author

would l i k e to express

Dr. A l e c M i t c h e l l , f o r h i s h e l p and course

of t h i s work.

colleagues

i n the

Much a p p r e c i a t i o n with

The

is given

fellow students

and

of several

f o r t h e i r h e l p f u l c r i t i c i s m of the

his

discussions

f a c u l t y members. Chacklader

of

the

gratifying.

f o r t h e many h e l p f u l

other

to

throughout

been extremely

w o u l d a l s o l i k e t o t h a n k Dr. A . C D . Ballantyne,

guidance

cooperation

i n d u s t r y has

his gratitude

The and

Dr.

author A.S.

d r a f t manu-

script. The A g e n c y and

support

of the Canadian

o f t h e M i n i s t e r i o da

International

Development

I n d u s t r i a e Come'rcio,

Brasil,

are g r a t e f u l l y acknowledged. Special for t h e i r support

t h a n k s a r e due during

to E l e c t r o m e t a l

this project.

x

Acos f i n o s

S.A.,

1

CHAPTER 1 INTRODUCTION 1. 1

Introduction With the

for

the a e r o s p a c e ,

industries, important now

i n c r e a s i n g demand f o r h i g h q u a l i t y m a t e r i a l s n u c l e a r and

Vacuum I n d u c t i o n

Melting

p o s i t i o n a s an a l l o y - m a k i n g

well understood

it i s very process

other highly sophisticated

likely

contamination

has

reached

process.

Due

and c o n t r o l l e d t e c h n o l o g i c a l that i t will

f o r some c o n s i d e r a b l e The

(VIM)

time

much l e s s c o n t a m i n a t i n g

one

than

i n t o the

advantages primary

future.

a t m o s p h e r e as a s o u r c e

and even a m e d i o c r e

a very pure

gas.

of

vacuum i s

One

must

aware, however, of the e f f e c t s of the v a r i o u s p r e s s u r e tive

very

to i t s

k e e p i t s p o s i t i o n as a

idea of removing the i s n o t a new

a

be sensi-

r e a c t i o n s o c c u r r i n g in s t e e l or high-temperature

alloy-

making. Induction

heating i s , without

q u e s t i o n , one

of

the

c l e a n e s t and e a s i e s t t o c o n t r o l h e a t i n g methods a v a i l a b l e , offering

"con t a c t l e s s " h e a t i n g w i t h

t u r e c o n t r o l and reduced

o r no p r o b l e m

of

in operating

tempera-

under

pressures. S i n c e we

for

little

a high degree

very expensive

are d e a l i n g with

a primary

melting

alloys, i t is clear that a

process

continuous

2

process i s not f e a s i b l e . bringing

Batch o p e r a t i o n i s then

i n t o the s i t u a t i o n

the need

necessary,

for a container.

c o n t a i n e r s h o u l d be a b l e t o r e s i s t t h e t e m p e r a t u r e s molten

metals

and,

within

a reasonable

This

of

the

a t t h e same t i m e , k e e p t h e h e a t l o s s e s level.

It is also clear that

the

c o n t a i n e r s h o u l d i n t e r a c t to the minimum e x t e n t p o s s i b l e w i t h the m e t a l .

Although

t h e two

first

d e m a n d s a r e f u l f i l l e d by

s e r i e s o f c o n v e n t i o n a l r e f r a c t o r y m a t e r i a l s , the l a s t poses

the b i g g e s t d i f f i c u l t y ,

Even refractories

to

though

are u s u a l l y

utilize.

non-oxide

f o r VIM

m a t e r i a l s have been

used

as

f u r n a c e s , most o f the p o t e n t i a l c a n d i -

dates amongst these m a t e r i a l s f i n d severe economic What i s t h e n s e e n

one

r e d u c i n g the number of p o s s i b l e

a t e r n a t i v e s to a handful of m a t e r i a l s which expensive and.hard

a

limitation.

i s t h e e x t e n s i v e use o f o x i d e s o r

mixtures

o f o x i d e s i n t h e f o r m o f p r e f i r e d , o r rammed i n p l a c e , o r brick/cement

lining

ature Nickel-based

as c o n t a i n e r s f o r s t e e l s a n d h i g h alloys.

To a g g r a v a t e

the chemical

o f t h e a l l o y s made by VIM reactive

alloying

interaction

contain relatively

a t l o w e r p r e s s u r e s due +

problem,

most

l a r g e amounts

a d d i t i v e s s u c h as T i , A l , e t c . , o r , i n

case of s t e e l , carbon, the l a t t e r becoming

•C

temper-

0

=

of

the

much m o r e r e a c t i v e

to the e f f e c t of r e a c t i o n CO

(g) .

In a d d i t i o n , h i g h q u a l i t y m a t e r i a l s r e q u i r e h i g h heat-to-heat reproducibility ability

i n p r o p e r t i e s , maximum

( s i n c e they a r e , per se, hard to work) and,

hot-workin

the

3

case of h e a t - r e s i s t i n g All

alloys, excellent

these c h a r a c t e r i s t i c s are influenced

element contamination from r e f r a c t o r y

no d i s s o l u t i o n ) a refractory.

achieved. extent

Recognition part

i f the best

Refractories

stability

(no

desired in

i n the r e f i n i n g process

becomes

vacuum m e l t i n g

i s t o be

practice

be a t t a c k e d

processed

thoroughly

r e f r a c t o r y / a 11oy

reaction-

t h a t t h e r e f r a c t o r i e s a r e one o f

should

by t h e a l l o y s b e i n g

best

trace

products

as one o f t h e p a r a m o u n t p r o p e r t i e s

unavoidable reaction the

g r e a t l y by

interaction.

components taking

then e s s e n t i a l

properties.

and i n c l u s i o n s , both l i k e l y

In V I M , o n e t h e n s e e s c h e m i c a l

the

creep

t o a minimum

and t h e p r o d u c t o f any

defined

combinations.

i n order

to

achieve

1.2

Literature 1.2.1

Survey

Metal-Refractory 1.2.1.1

Although definite

secondary

Under

Vacuum

V a p o r i z a t i on

vaporization

possibility

extensively

Interactions

of r e f r a c t o r y

(1), this

i n the p r e s e n t

importance,

problem w i l l

study

since

i t is

oxides

is a

n o t be d e a l t w i t h likely

compared t o d i r e c t c h e m i c a l

t o be o f

a t t a c k by

the m e l t . 1.2.1.2

Dissolution

The s i m p l e s t

process

that

oxide

which

X and oxygen a r e s o l u b l e

the

in contact with

of

a metal Y, in

to a certain extent,

is

AG,

(1)

dissolution XO = X This

and,

Refractories

can o c c u r when a p i e c e

refractory both

XO i s b r o u g h t

of

given

given

+ 0

i n Y

i n Y

reaction w i l l

occur at the m e t a l - o x i d e

s u f f i c i e n t time, achieve

the s o l u b i l i t y

interface limit

by t h e p r o d u c t h

When-h

and h

- .

x o

and a

x Q

A

Q

e-".>"

(2)

a r e t h e a c t i v i t i e s o f X, fj and XO,

respectively. Table of oxides most

1 presents

in iron

a t 1600°C

of the d i s s o l u t i o n

pressure

sensitive,

thermodynamics

the s o l u b i l i t y p r o d u c t s and a t m o s p h e r i c

processes

pressure.

l i s t e d in Table

one can use them a g u i d e l i n e s

o f the d i s s o l u t i o n

process.

for a series Since

1 are not f o r the

5 S h o u l d X be h i g h l y v o l a t i l e a n d i n s o l u b l e ( o r a l m o s t ) , s u c h as Mg o r Ca i n i r o n , t h e d i s s o l u t i o n w i l l saturation

of the bath w i t h oxygen

f o r m a t i o n o f a FeO at

s l a g , due

the metal/vacuum MgO

(5).

proceed

This will

to

l e a d to the

t o t h e e v a p o r a t i o n o f Mg

(or

Ca)

i n t e r f a c e , d i s p l a c i n g the r e a c t i o n

= Mg + 0

by t h e c o n s t a n t r e m o v a l

o f one

o f the p r o d u c t s .

be o b s e r v e d , h o w e v e r , w h e n t h e p r o c e s s k i n e t i c s

T h i s may are

not

very

sluggish. All they w i l l

these p r o c e s s e s are o b v i o u s l y u n d e s i r a b l e s i n c e

i n t r o d u c e an u n a c c o u n t e d

a l l o y i n g element

o x i d i z e the b a t h , most p r o b a b l y c o m p r o m i s i n g of the r e s u l t i n g

Reaction With A l l o y i n g 1.2.1.3.1

elements

above

are p r e s e n t .

has been

a steady decrease

Elements

Carbon

p i c t u r e changes,

most i m p o r t a n t e l e m e n t confusion

the p r o p e r t i e s

alloy.

1.2.1.3

The

and

h o w e v e r , when

alloying

In t h e c a s e o f s t e e l s , c a r b o n

i s the

i n VIM

most

generated. in carbon

and t h e one

over which

Although a l l authors

c o n t e n t o f t h e a l l o y , as

observe the

r e a c t i on XO +

C

= CO + X

p r o c e e d s , a g r e a t d e a l o f m i s u n d e r s t a n d i n g has been about

by f a i l i n g t o a c k n o w l e d g e

the k i n e t i c a s p e c t s of the

p r o c e s s and t r y i n g to compare r e s u l t s different initial

carbon

brought

contents.

from s t e e l s with

The e x p e r i m e n t s

by

widely Bennett

6 e t a l . ( 6 ) , who s t a r t e d h i s t e s t s w i t h a ' 0 . 2 % C s t e e l crucible

a n d o b s e r v e d r e a c t i o n t i m e s o f up t o 85

showed the achievement about

8 ppm.

o f a c l e a r minimum

This i s in obvious

steel

c o n t e n t , somewhere

10 ppm.

has b e e n - f o u n d " ,

( 7 ) , who

minimum

Although Oberg

p o i n t o u t t h a t "no w o r k c o v e r i n g a w i d e r r a n g e concentration

level, of

c o n f l i c t as t h e a u t h o r s

and o b s e r v e d a peaked above

minutes,

oxygen

p o i n t o u t , w i t h t h e p r e v i o u s r e s u l t s o f Moore w i t h a 0.1%C

i n a MgO

started

i n the

et al.(8)

o f carbon

the k i n e t i c study o f Machlin

( 9 ) h a s s h o w n w h a t s h o u l d be e x p e c t e d i n s u c h a c a s e . s t a r t s with a high carbon

oxygen

I f one

a c t i v i t y melt, the d i s s o l u t i o n

step

MgO = Mg. + 0 and t h e d e o x i d a t i o n s t e p C + 0 = CO will

define a kinetic equilibrium fixing

oxygen

level

in the bath.

As t h e c a r b o n

during this p e r i o d , the steep ascendent equilibrium hyperbole will the " f r e e oxygen

a steady-state c o n t e n t goes

down

s i d e o f t h e C/0

be r e a c h e d a n d w h a t O b e r g

uptake" w i l l

prevail.

T h i s whole

called

p r o c e s s can

be d e s c r i b e d b y a c u r v e a s F i g . 1, w h e r e o n e o b s e r v e s an : initial oxygen

d e o x i d a t i o n , then a s t e a d y - s t a t e and f i n a l l y a c o n t e n t i n c r e a s e , due t o t h e l a c k o f s u f f i c i e n t

flushing.

I t i s easy t o u n d e r s t a n d t h a t what Moore

a c t u a l l y , was j u s t

an o v e r l a p p i n g o f b o t h

p r o c e s s e s , d u e t o an i n j u d i c i o u s s e l e c t i o n

fast CO

observed,

unsteady-state of carbon

content.

7

The

understanding

paramount importance

f o r the o p e r a t i o n

it will

permit

the best

content

t o be

reached.

Since s t a t e and o f the

of t h i s process

deoxidation

o f VIM

and

consumption

furnaces,

since

the minimum i n c l u s i o n

the minimum oxygen c o n t e n t

the carbon

i s c l e a r l y of

a t t a i n e d at

rate are both

steady-

direct

functions

dissociation reaction XO - X + 0

it is evident criteria in

that those

two

conditions will

be

for assessment of r e f r a c t o r y s t a b i l i t y

adequate and

adequacy

VIM. Schaffer

dynamics of the With e x t e n s i v e bath, the

(10)

and

various

others

have c a l c u l a t e d the

melt-refractory

s i m p l i f i c a t i o n s he

c o n t a i n i n g 0.4%C

reactions

found

thermo-

possible.

t h a t , f o r an

the e q u i l i b r i u m pressures

iron

o f CO

for

reaction X0 + C = CO + X

w o u l d be as g i v e n usual

operating

expect

the from

take

in account

prevail there

pressures

reduction

able

2.

in Table

As t h e y

o f VIM

of the

furnaces

only

(80y),

f a c t that these

H o w e v e r one re 1 a t i o n s h i p s

the

should favour-

should

also

shou1d

f o r the m e t a l - c r u c i b l e - v a c u u m i n t e r f a c e , where

i s no n u c l e a t i o n

b a r r i e r f o r CO

formation.

d e e p e r i n t h e me 1 1 - c r u c i b l e i n t e r f a c e , t h e C/0 t i on m u s t be s u f f i c i e n t t o o v e r c o m e t h e the s u r f a c e

one

r e f r a c t o r i e s t o be h i g h l y

a thermodynamic viewpoint. the

are a l l w e l l over

forces

(CO

n u c l e a t i n g then

As o n e

goes

supersatura-

f e r r o s t a t i c head as b u b b l e s )

and

otherwise

8

the a t t a c k has to proceed

as d i s s o l u t i o n o f the o x i d e ,

( e n h a n c e d b y t h e l o w fJ c o n t e n t of 0 through

the bath

of a C rich bath),

a n d CO f o r m a t i o n

transport

and d e s o r p t i o n

at the

s urface . Turillon

(11) and o t h e r s

tion of iron melts and

recognized

reaction. F i g . 2.

have s t u d i e d t h e d e o x i d a -

under Vacuum I n d u c t i o n

the importance

He o b s e r v e d

Melting

of the r e f r a c t o r y

the behaviour

conditions decomposition

p r e d i c t e d by M a c h l i n , i n

T u r i l l o n also noticed that, i n h i s MgO/spinel

c r u c i b l e s , a t t h e p o i n t o f m i n i m u m C^ a n d 0_ c o n c e n t r a t i o n preceding

the " f r e e oxygen uptake", the d e o x i d a t i o n

refractory decomposition

rates, determined

were e q u a l , w i t h a value

of approximately

and t h e

independently, 1.5 ppm 0 / m i n .

A c o n s i d e r a b l e n u m b e r o f s t u d i e s h a v e a l s o b e e n made taking i n account

the carbon

boil

conditions, i.e., critical

crevice sizes f o r nucleation of bubbles, needed, e t c . Besides

the conventional

supersaturation treatment

o f Darken

( 1 2 ) , K r a u s ( 1 3 ) h a s c a l c u l a t e d t h e c h a r a c t e r i s t i c s o f CO bubbles

i n vacuum carbon

deoxidation.

He p r e s e n t e d

bubble

c h a r a c t e r i s t i c s g r a p h i c s , s h o w i n g t h e maximum a c t i v e d e p t h bubbling,

of

t h e minimum s u p e r s a t u r a t i o n needed f o r b u b b l e

n u c l e a t i o n , a n d t h e e f f e c t o f s e v e r a l o t h e r v a r i a b l e s on t h e degassing

processes.

He p o i n t e d o u t t h a t , i f t h e n u c l e a t i o n

frequency

as a f u n c t i o n o f p r e s s u r e

known, t h e r a t e o f d e g a s s i n g mined.

Unfortunately,

during

and c o n c e n t r a t i o n the boil

was

c o u l d be d e t e r -

as Kinsman e t a l . (14) p o i n t o u t , t h i s

knowledge i s not a v a i l a b l e and should

d e p e n d on s e v e r a l

hard

9 c h a r a c t e r i z e f a c t o r s such as a g i t a t i o n of the b a t h , c h a r a c t e r i s t i c s of the c r u c i b l e , presence

of

surface

heterogeneous

nuclei, etc. It boil

i s important

i s the major

substantial

to keep i n mind, t h a t , a l t h o u g h

CO e l i m i n a t i o n p r o c e s s , o n c e

oxygen

removal

still

the

i t subsides,

h a p p e n s by s u r f a c e

desorp-

tion. 1.2.1.3.2 Precipitation basically

Other Al l o y i n g

hardening nieke 1-based

on a l u m i n i u m - ,

and

achieve t h e i r high temperature uncommon t o f i n d a l l o y s w i t h

Elements alloys

rely

t i t an i u r n - r i ch p r e c i p i t a t e s t o strength (15). up t o 4 - 5 %

I t i s not

Ti+Al

(Table 3).

A

will

show t h a t

both

\

b r i e f l o o k a t an o x i d e s t a b i 1 i t y A1^0^

and TiOg

a r e among t h e most s t a b l e o x i d e s .

elements

will

Although

vacuum w i l l

present then, r e a c t i v i t y problems

tions, i t is still main d r i v i n g

n o t l i k e l y p l a y any

important

Zr,

of ceramics

( 1 6 , 17,

18)

role in these

reac-

of the

i s the p o s s i b i l i t y

of

have s t u d i e d the

by N i c k e l a l l o y s .

rapid wetting of refractories

Al , T i and

with crucibles.

rich in reactive elements.

Various authors

observed

These

t o s t u d y t h e m s i n c e one

f o r c e s f o r t h e u s e o f VIM

producing alloys

wettability

diagram

C, a n d

Sutton

(19)

by a l l o y s c o n t a i n i n g

found t h a t w e t t i n g i n c r e a s e d with

content of the a l l o y i n g a d d i t i o n .

Snape (20) o b s e r v e d

t h e w e t t a b i l i t y o r d e r o f v a r i o u s a l l o y s i s t h e same i n ent r e f r a c t o r i e s s u b s t r a t e s . wetting of alumina

He

the that differ-

a l s o n o t i c e d the i n c r e a s e d

c r u c i b l e s by r e a c t i v e a 1 1 o y i n g

elements

in

10 a l a r g e number o f commercial nieke 1 -carbon

high temperature

and

alloys.

The p r o c e s s i n q u e s t i o n , f o r a N i - T i Alumina

alloys

c r u c i b l e , would

a l l o y in a pure

be d e s c r i b e d by

f-T_i + A l „ 0 _ = J-Ti0 . 9

t.

+ 2AJ_ A1 0 2

3

It i s c l e a r t h a t the aluminum

content of the bath

play a r o l e i n the e q u i l i b r i u m . S u t t o n found s t r o n g in w e t t a b i l i t y dissolution

depending

o f the Ti0£

activity will

on t h e T i / A l formed

r a t i o i n the a l l o y .

made by S n a p e ,

K a m a m u r a e t a l . ( 2 2 ) who

An e x t e n s i v e s t u d y

G u p t a e t a 1. ( 2 1 )

noted the a l t e r a t i o n

r e f r a c t o r y s u b s u r f a c e l a y e r s and e n r i c h m e n t s

E f f e c t of Minor

use o f pure s i l i c a

contact with either steel

and

s u f f e r e d by in Cr, Ti

the

and

Components

refractories

o r n i e k e 1-a 1 1 o y s

r u l e d o u t due t o t h e low s t a b i l i t y

under vacuum i n s h o u l d be

vast number o f commercial

clearly

of SiO^ in presence of C

a t low p r e s s u r e s , o r o f A l , T i a l l o y i n g e l e m e n t s . refractories

in which

an i m p o r t a n t r o l e as a b i n d i n g a g e n t - - s u c h

tion

of

elements.

1.2.1.4

aluminous

The

i n t h e c r u c i b l e and i t s f i n a l

i n c r e a s i n g the e r o s i o n .

t h o s e r e a c t i o n s was

The

variations

be i m p o r t a n t i n t h i s p r o c e s s - - a l a r g e s o l u b i l i t y

in the c r u c i b l e

other alloying

will

But,

silica

as m u l l i t e ,

the plays silico-

and h i g h - a 1 u m i n a - - h a s p r e c l u d e d i t s c o m p l e t e e l i m i n a -

from the vacuum i n d u c t i o n m e l t i n g scene.

o f s i l i c a and i t s p r e s e n c e i n most ores pose

The

abundance

economical

11 problems in making r e f r a c t o r i e s with Fe^Og i s a l s o o f t e n p r e s e n t

very

as i m p u r i t y

l o w - s i l i c a content.

(23), i t s removal

b e i n g e c o n omi c a l l y un f e a s i b l e . The increased

work o f Graham e t a l . ( 2 4 ) i n t e r a c t i o n t o be e x p e c t e d

shows c l e a r l y the as t h e

silica

content

of

s i ' l i c o - a , l umi n o u s r e f r a c t o r i e s i s i n c r e a s e d .

Machlin

estimated

a 10

content

of a

fold

steel

increase

melted

Hoffmann.

in the steady-state

i n a 1% S i 0 ^ - M g O c r u c i b l e , u s e d Although

some s u g g e s t

able to consume the s i l i c a silica

reduction

t o r y , one

oxygen

t o be

possible decrease

in the working

the

Fisher

t h a t a wash heat

c o n t r o l l e d by

must c o n s i d e r

by

should

i n p o r o s i t y and

i n s t r e n g t h • a-ssoci ated'Wi th the

Most l i k e l y ,

wetted

altered layer will

s p a l l when t h e

residual

(23)

dissolved in

next

heat,

as t h e

explanation reducing

(25)

who

observed

a i r d r i e d a t 2 2 5 ° C and

same c a r b o n

consumption

then

wash-heat.

and

gases

i n r e f r a c t o r i e s can

in

alloys.

They t h e r e f o r e

the

better

crucibles is

given

vacuum d r i e d produced

the

s t e e l as a c r u c i b l e

This would i n d i c a t e that absorbed

Snape a l s o r e p o r t e d content

be m a j o r s o u r c e s

of

purposes

at

( c r u c i b l e s o f 206

i n c r e a s e d w e t t a b i l i t y due

(although

water

oxidation

r e c o m m e n d e d an a i r d r y i n g

h. f o r r e s e a r c h

increased silica

metal,

that a c r u c i b l e which

i n the molten

a f t e r one

1 2 5 0 ° C f o r 24

A much

this

favorable e f f e c t s of a "wash-heat" in

" p o l l u t i o n " p o t e n t i a l of the

by H u n t e r & T a r b y was

b i n d i n g phase i s absent.

f o r the

the

a n d / o r be

refrac-

corrosion

intergranu1 ar s i 1 i c o - a l u m i n a t e s .

solidifies

the

the

of the

a f t e r teeming,

be

face, causing

d i f f u s i o n i n the

increase

and

cm

to

some i n c r e a s e i n p o r o s i t y

).

12 was

also

experimented). As b o r o n

oxide

o t h e r o x i d e s , i t has a d d i t i on s - - a s

refractories

ties.

and

several

of b o r i c a c i d

bonds f o r v a r i o u s a p p l i c a t i o n s .

et a l . ( 2 6 ) showed, a l l o y s produced

c o n t a i n i n g 1.2%

B

2^3

in

cannot

which

hot w o r k a b i l i t y

In t h e c a s e o f h i g h q u a l i t y m a t e r i a l s i n w h i c h i s mandatory, the d i f f e r e n t l e v e l s of

t i o n s d u r i n g the l i f e

properrepro-

contamina-

o f t h e c r u c i b l e r e p o r t e d by D e c k e r

be t o l e r a t e d .

As W i n k l e r

(23) o b s e r v e s ,

stability

are used

during the manufacture

et

wetting

and e r o s i o n o f t h e c r u c i b l e a r e p r o m o t e d i f b i n d e r s o f chemical

MgO

c o n t a i n e d some b o r o n ,

f o r v a r i a t i o n s i n c r e e p and

ducibility

al.

f l u x t o MgO

been u s e d - - i n the form

chemical

H o w e v e r as D e c k e r

accounted

i s a powerful

of

lower the

c r u c i b l e , as t h e y a r e p r e f e r e n t i a l l y d e c o m p o s e d . 1.2.1.5 Although e x t e n s i v e and observed. mental

K i n e t i c Aspects

the thermodynamic p r e d i c t i o n s

v i o l e n t c o r r o s i o n , t h a t i s not what i s u s u a l l y

In a d d i t i o n , d i s c r e p a n c y

r e s u l t s from

accounted

d i f f e r e n t authors

It i s important

and

i s found between e x p e r i which

cannot

f o r s i m p l y by d i f f e r e n t e x p e r i m e n t a l

open and

be

techniques.

to keep i n mind t h a t f a c t o r s such

closed p o r o s i t y , mechanical

s i z e d i s t r i b u t i o n , temperature

agitation

suggest

r e s i s t a n ce , g r a i n s i z e of the t e s t , degree

(frequency of current, size of furnace, etc.)

play a definite

role in determining

the v a r i o u s r e f r a c t o r i e s .

as

of will

the r e a c t i o n k i n e t i c s f o r

13

Turillon

(27)

noticed

minimum oxygen c o n t e n t f u s e d MgO

they

mechanical transport

latter

resistance.

Machlin

can

lower thermal

assumed the

c o n t r o l l e d a t the c r u c i b l e / m e t a l

to pose l i m i t a t i o n s to the p r o c e s s .

i.e., depletion

a t the

c e r t a i n l y be e x p e c t e d

differential

influence

main

hardly

ing

place

by d i s c r e t e p i e c e s

is

most

variations the

mass

interface.

of

by

refractory

Once a p i e c e that i t will

The

i t s much i n c r e a s e d

area.

higher

the

obvious

phenomena,

helping

the

frequency,

hence, less erosion

o f r e f r a c t o r y has be

from i t s

rate of transport

of bond s o f t e n i n g , again

of refractory grains.

likely

It

bath.

in i n c r e a s i n g the

expected.

it

stabilities.

a p p e a r as e f f e c t s on

t h e a g i t a t i o n o f t h e m e l t and

very

occur,

t o be t r u e w h e n t h e r e

e f f e c t of temperature, apart

a l s o be one

be

metal/vacuum

as S n a p e o b s e r v e d , much o f t h e o x y g e n i n t a k e

The

will

to

phase i s the

corroded

t r a n s f e r c o e f f i c i e n t at the m e t a l / c r u c i b l e

i n t o the

and

may

interface will

not

in c r u c i b l e p a r a m e t e r s w i l l

falling

shock

Although this

reaction of phases of various

the metal takes

or

results,

reaction and

i s c l e a r t h a t f o r the purpose of m o d e l l i n g ,

Besides,

the

r e a c t i o n i t s e l f proceeded f a s t enough

be s o f o r c r u c i b l e s i n w h i c h t h e one,

in

g i v i n g the b e t t e r

have, unfortunately,

i n t e r f a c e s , i . e . , the not

differences

a t t a i n a b l e w h e n u s i n g r a m m e d MgO

c r u c i b l e s , the

although

sharp

loosenthe

i s to

lower be

been e r o d e d i t i s

d i s s o l v e d a t a f a s t r a t e due

to

14 1.2.2

R e f r a c t o r y P r a c t i c e i n VIM

Besides

the c l e a r importance

of the thermodynamic

s t a b i l i t y o f t h e l i n i n g m a t e r i a l , we h a v e s e e n actual

s t r u c t u r e o f the r e f r a c t o r y w i l l

in the k i n e t i c s o f the a t t a c k process.

that the

play a definite

role

I t i s then i n s t r u c t -

ive to study the d i f f e r e n t r e f r a c t o r y p r a c t i c e s applied i n VIM,

comparing Table

t h e i r advantages 4 presents

and drawbacks.

various p r a c t i c e s quoted

l i t e r a t u r e a n d t h e f o l l o w i n g c a n be Laboratory

furnaces

in the

observed.

and s m a l l f u r n a c e s

up t o a b o u t

25kg c a p a c i t y u s u a l l y employ p r e f i r e d c r u c i b l e s .

Although

i t w o u l d be p o s s i b l e t o u s e r a m m e d l i n i n g s , t h e l a b o u r

costs

a r e p r o h i b i t i v e . As t h e f u r n a c e s i z e i n c r e a s e s t h e l i m i t f o r prefired

c r u c i b l e s i s reached

l i n i n g becoming more e c o n o m i c a l

a t about

2 5 0 k g , t h e rammed

as t h i s v a l u e i s

approached

(51). F o r i r o n and n i c k e l m e l t i n g p u r p o s e s , r e l i e s on h i g h p u r i t y MgO (96%A1 0 , 2%Si0 ) 2

3

2

one u s u a l l y

(96%MgO, 2%Si 0 , l % F e 0 ) 2

(51), although

z i r c o n i a c r u c i b l e s c a n a l s o be

2

Mg0.Al 0 2

3

3

or A1 0 2

3

or stabilized

used.

As C h i l d e t a l . ( 5 1 ) p o i n t s o u t , h o w e v e r , p r e f i r e d crucibles are not considered f o r industrial to the high p r i c e and s h o r t l i f e s . more dangerous wide and cause

than

a p p l i c a t i o n s , due

B e s i d e s , c r a c k s a r e much

i n rammed c r u c i b l e s , s i n c e t h e y

can open

leakage.

Ramming m i x t u r e s

f o r Induction

by a n u m b e r o f m a n u f a c t u r e r s . h o w e v e r , when e x t e n d i n g

Care

Furnaces

are

produced

s h o u l d be e x e r c i s e d ,

t h e i r use t o Vacuum I n d u c t i o n

Melting.

15 High s i l i c a tion

linings

f o r i n s t a n c e , q u i t e common i n A i r

f u r n a c e s , m u s t be b a n n e d i f t h e b e s t r e f r a c t o r y p r a c t i c e

i s t o be a c h i e v e d .

The

Fe^O^

c o n t e n t m u s t a l s o be k e p t

a l t h o u g h i t i s an e x c e l l e n t a d d i t i v e t o p r o m o t e MgO due

Induc-

to i t s f 1 u x i n g a b i 1 i t y .

present

a

Winkler

(15) p r e f e r s to s e t the upper

low o x y g e n

l / U F ^ O ^ . MgO

Although

Child et a l .

c r u c i b l e as a t y p i c a l

low,

sintering, (51)

VIM m a t e r i a l ,

l i m i t at 0.5%Fe202> i f

l e v e l s a r e t o be a t t a i n e d .

Ramming m i x t u r e s

c a n be e i t h e r w e t

ramming b e i n g made, i n both

o r d r y rammed,

cases, using a metal

the

p l a t e mould

or a s i m i l a r k i n d o f c o r e . The

ideal

g o a l i n p r o d u c i n g a rammed l i n i n g

some 3 0 % o f t h e t h i c k n e s s f u l l y at the working

low p o r o s i t y

f a c e - - t h e r e s t o f t h e l i n i n g s h o u l d be

i n g l y s i n t e r e d and hence date thermal

s i n t e r e d , with

i s to have

more p o r o u s

and m e c h a n i c a l

decreas-

and more a b l e t o accommo-

stresses.

This less sintered

l a y e r a c t s as a c u s h i o n , h o l d i n g t h e h a r d s i n t e r e d " c r u c i b l e " in place.

T o a c h i e v e t h i s , s e v e r a l f a c t o r s m u s t be t a k e n

into

account. The

grain size distribution

s h o u l d be s o a s t o

the d e s i r e d p o r o s i t y i n the u n s i n t e r e d zone dense

structure necessary

distributions

to the w o r k i n g

and a c h i e v e

face.

the

Usually

are very s i m i l a r to the F u l l e r curve

Regarding

produce

(5).

c o m p o s i t i o n , the ramming m i x t u r e w i l l

c o n s i s t o f main c o n s t i t u e n t s and a b i n d i n g a g e n t . of a MgO/MgO.Al^0^.spine1 mixture, to promote s i n t e r i n g

always

In the

f o r i n s t a n c e , SiO^ i s

( i n a m o u n t s up t o 3% ( 5 ) ) .

these

Care

case added

should

16

be e x e r c i s e d when

s e l e c t i n g the amount and c o m p o s i t i o n

of the

b i n d i n g a g e n t s i n c e i t i s u s u a l l y l e s s s t a b l e a n d , as f a r as attack resistance i s concerned, One s h o u l d u s e t h e m i n i m u m ing

at the d e s i r e d f i r i n g

d e l e t e r i o u s to the

lining.

amount n e c e s s a r y to a c h i e v e temperature.

sinter-

O b v i o u s l y , as t h e

amount o f b i n d i n g agent i s d e c r e a s e d , t h e f i r i n g

temperature

m u s t be i n c r e a s e d u s u a l l y i n t r o d u c i n g t e c h n i c a l

difficulties.

D e p e n d i n g on t h e k i n d o f c o r e u s e d mixture,

firing

c a n be d o n e i n t w o w a y s .

template

was u s e d i n r a m m i n g t h i s w i l l

place during firing that will

quent

I f a mild

steel

u s u a l l y be l e f t i n

m e l t away i n a f i r s t wash

provide the c o r r e c t f i r i n g

case, the lining be f i r e d

and w i l l

f o r ramming t h e

temperature.

In t h i s

s h o u l d be a l l o w e d t o d r y c o m p l e t e l y

under vacuum, t o minimize

wood c o r e i s u s e d ,

firing

in the furnace.

c a n be d o n e e i t h e r b y h e a t i n g up a

c a n be u s e d

to f i r e

g r a p h i t e c o r e be u s e d , vacuum, t o m i n i m i z e core

initial

The use o f t h e wood c o r e i s recommend-

e d s i n c e i t c a n be r e m o v e d a n d a g r a p h i t e c o r e w i t h dimensions

subse-

I f a graphite or a

g r a p h i t e c o r e o r b y r e m o v i n g t h e c o r e a n d m e l t i n g an charge

and then

i r o n o x i d a t i o n and

i r o n o x i d e p i c k - u p by t h e l i n i n g .

heat

up t h e l i n i n g .

the f i r i n g

imprecise

Should a

s h o u l d n o t be made

the r e a c t i o n between the l i n i n g

under and the

(5 ). The

main problem

experienced with monolithic

however, i s c r a c k i n g , s i n c e the l i n i n g mechanical

and thermal

uncommon t o p r o d u c e

stresses.

a lining

with

linings,

i s subjected to severe

During

firing

i t i s not

c r a c k s , p a r t i c u l a r l y as t h e

17

lining

dimensions,

and hence

the s t r e s s e s , are i n c r e a s e d .

When a c r a c k i s f o u n d a f t e r f i r i n g , t h e c r u c i b l e m u s t a l l o w e d t o c o o l , and the c r a c k f i l l e d w i t h cement. thermal

This

c y c l e and the i n t r o d u c t i o n o f a d i f f e r e n t m a t e r i a l

can p r o d u c e

new

cracks.

with large furnaces.

T h i s becomes a very d i f f i c u l t

As S c h l a t t e r a n d S i mko v i ch ( 3 0 )

concerning r e f r a c t o r i e s performance volume s t a b i l i t y , escalated".

(tightness or construction,

this problem

they used r e f r a c t o r y brick/cement excellent crucible lifes.

i n a 6 0 , 0 0 0 l b VIM c o n s t r u c t i o n and

They used Korundal

b o n d e d w i t h M u l l i t e ) as a b a c k i n g

lining,

thermal

or Magnesia

and e i t h e r t h i s

(MagneT) as t h e w o r k i n g

present industrial

problems

r e s i s t a n c e t o c r a c k i n g and s p a l l i n g ) a r e

To a v o i d

stability

problem

pointed

o u t , "as t h e s i z e o f f u r n a c e i s i n c r e a s e d , a l l t h e

spinel

be

lining,

XD

due

furnace,

reported (Alumina

t o i t s good bonded

the l a t t e r

practice in large furnaces.

with

being

Due

to

the the

h i g h d e n s i t y o f t h e XD b r i c k , i t s h o w e d b e t t e r r e s i s t a n c e t o FeO

s l a g s than a 90% Alumina

(28) s t u d i e d the c h e m i c a l

ramming mix

stability

w i t h z i r c o n i a and magnesi te-chrome in contact with d i f f e r e n t carbon observed

t h a t the performance

(29).

Simkpvich

of Korundal commercial

activity

XD as

refractories,

alloys.

t h e s a m e f o r t h e same a l l o y , as f a r a s

consumption

was

As t h e a u t h o r s

b e h a v i o u r o f t h e Z i r c o n i a c r u c i b l e was justify,

He

o f the t h r e e c o m p o s i t i o n s

essentially

concerned.

compared

found,

was

carbon the

indeed d i f f i c u l t to

s i n c e the h i g h e r p o r o s i t y alone would

o v e r r i d e the h i g h e r thermodynamic s t a b i l i t y .

be u n l i k e l y t o The

comparable

18 behaviour present

o f m a g n e s i t e - c h r o m e and no s u r p r i s e , s i n c e

and

10.5%

^^ °3

and

the

z i r c o n i a c r u c i b l e has

z

the

k i n e t i c basis only

the

the oxides

This

in practice.

carbon contents

these in the

system.

Chester

(52)

to the

in lining

very

but

and

melting

coils.

(larger furnaces)

not experience

penetration

d e p t h o f low

a

possible

In t h e

of

be

In that

the

induced

high the

progressively

case

of

lower

i t is likely that

further heating, frequency

used

use

furnaces.

between the b r i c k s w i l l

metal w i l l

melting,

dangerous s i t u a t i o n

i t is quite

frequency

improved

e a r l i e r by

recommended the

frequency

h e a t e d as i t a p p r o a c h e s t h e

Renkey et a l .

l i f e when b r i c k s w e r e

in induction

metal penetrating

net

r e s u l t s f r o m one

been r e p o r t e d

difficult

melting

expected

d e f i n i t e l y t h e weak l i n k

c a u s e d by j o i n t p e n e t r a t i o n induction

test, detrimental

o r by

observed, in a i r induction

i n s t e a d o f ramming m i x t u r e s ; l a t t e r , due

(30)

the b e s t

the j o i n t s are

substantial increase

to the

g o o d b r i c k l a y i n g and

T h i s e f f e c t has

who

validity

Simkovich

are

encountered.

e f f e c t s are more

are e s s e n t i a l to obtain

linings since

resistance,

Although this point is

"close size tolerances,

mortars"

abrasion

ZrO^)

to give even b e t t e r r e s u l t s .

(29),

in a

M g O / A T ^ O ^ ( M a g n e l ) b r i c k was

e m p h a s i z e d by S c h l a t t e r a n d

of

( i n c l u d i n g M g O j A ^ O ^ and

fact that gives

The

behaviour

surface)

e s p e c i a l l y s i n c e s u r f a c e / v o 1 ume than

2

u s e d (5u a t the b a t h

f o r the

the

17.4%Cr 02

to f i n d i t s e x p l a n a t i o n

(porosity, strength,

CO

is exactly

The

2

in question

l e s s s t a b l e than

shou1d

former contained

l a t t e r 10%S i 0 .

e t c . ) , s i n c e at the pressure all

a 1umina-si1ica

due

to the

current.

this large

of

19

Bonchack an i n d u s t r i a l

(47) r e p o r t e d s e v e r e e r o s i o n at j o i n t s

VIM

furnace, using Korundal

in

XD b r i c k s a n d

• C o r a l b a n d c e m e n t (82%A1 0 / 1 5 % S i 0 / 2 % T i 0 / 1 % F e 0 ) . 2

3

2

also observed t h a t the j o i n t s with

2

2

He

3

l e s s mortar were

less

e r o d e d a n d c o n c l u d e d t h a t t h e m o r t a r q u a l i t y was

inferior

the b r i c k q u a l i t y .

of a

A1 0^ 2

base

The

need

f o r the development

c e m e n t t o be u s e d b o t h w i t h K o r u n d a l

to

MgO/

XD a n d

Magnel

b r i c k s was t h e n s u g g e s t e d . I t i s i n t e r e s t i n g t o n o t e t h a t the use o f K o r u n d a l in t h e w o r k i n g

l i n i n g i s not i n d u s t r i a l

p r a c t i c e any

more,

s i n c e S c h l a t t e r (53) r e p o r t e d p e r s i s t e n t b o i l i n g w i t h steel

c o m p o s i t i o n s , due t o t h e 8.5%

Si0

2

present in

XD

certain Korundal

XD. The main

d i f f i cu 1 t y w i t h c e m e n t s

f a c t t h a t they s h o u l d bond at r e l a t i v e l y

to the b r i c k

and m o r t a r s

and a c q u i re s t r e n gth

low t e m p e r a t u r e s , s i n c e t h e w h o l e

furnace

be f i r e d f o r t h e s a m e t i m e a n d a t t h e s a m e h i g h as w e r e t h e b r i c k s .

l a r g e r amounts o f f l u x e s than in the b r i c k .

unstable

u n d e r VIM

b o r i d e s ) a n d may out e a r l i e r furnace bonded mm

Unfortunately,

cements

are r a t h e r and

l e a d t o c o n t a m i n a t i o n o f t h e m e l t , as p o i n t e d A 3000kg heat of s t e e l

f o r i n s t a n c e , w i t h 5% a r e a c o v e r e d b y a

o f cement

use

c o n d i t i o n s (as s i l i c a t e s , phosphates

f o r boron.

commercial

cannot

temperature

T h i s makes i t then n e c e s s a r y t o

most o f the f l u x e s used i n commerical

i s the

cement, w i l l

eroded.

in a

VIM

phosphate

a b s o r b a s m u c h as l . l p p m

per

20 1.2.3

Other

Apart

R e a c t i o n s Wi t h t h e L i n i n g

from

r e a c t i o n s i n v o l v i n g oxygen

(oxides) in

the l i n i n g , most o f t h e work done i s r e l a t e d t o d e s u l p h u r i z a tion

(de-S).

Sulphur

removal

by vacuum i s e x t r e m e l y

ineffect-

i ve, e i t h e r as gas 2S = S ( g ) 2

or as v o l a t i l e

compounds as

Sj_ + S = S i S ( g ) T.P. melts--which

Floridis

( 5 4 ) r e p o r t s 1.25h @ 6u i n C and S i r i c h

i n c r e a s e S a c t i v i t y - - a r e needed t o reduce

content to 50% o f i t s i n i t i a l and

reaction in steel

have been used:

value.

sulphur

S i n c e d e - S i s an

and N i - a l l o y making, three

import-

approaches

the use o f s l a g s , the p a i n t i n g o r c o a t i n g o f

the r e f r a c t o r i e s , and t h e use o f Rare

Earth Metals

(REM).

Ward e t a l . (55) t r i e d s e v e r a l d i f f e r e n t m e t h o d s o f adding

l i m e t o de-S a VIM s t e e l

marble

c h i p s was o f v e r y

formed

a r i n g around

area.

The use o f lime/water

presented

heat.

The use o f c a l c i n e d

l i t t l e e f f e c t since the lime r a p i d l y

the c r u c i b l e wall

reducing the contact

paste over the r e f r a c t o r i e s

the best r e s u l t s , with

very good de-S.

In t h e c a s e

of s p i n e l r e f r a c t o r i e s , however, the lime reacted with the r e f r a c t o r y and s w e l l e d , d e c r e a s i n g t h e i n n e r d i a m e t e r crucible.

A l s o , when u s i n g p u r e

c o a t i n g and adherent

metal

f r e s h a p p l i c a t i o n was m a d e . under

MgO r e f r a c t o r y , t h e CaO

was r e m o v e d a f t e r e a c h This process

present problems

head and a

i s only f e a s i b l e

vacuum due t o t h e h i g h f l u x i n g a b i l i t y

This would probably

of the

F e O h a s on l i m e .

w i t h an i n d u s t r i a l

scrap

21 charge.

A l s o , no o b s e r v a t i o n

i s made w i t h

regard to the'life

of the c r u c i b l e . The

u s e o f s l a g s i n VIM i s e x t r e m e l y

to the f a c t t h a t the whole process Although

very ingenious

proposed

i n p r i n c i p l e (56) i t i s extremely

will

processes

occurs

c u m b e r s o m e , due

in a sealed

f o r slag handling

Besides,

point.

to s o l i d i f y

are heated

Although

there are suggestions

here.

in the center

In o r d e r t o g u a r a n t e e

f l u x i n g a d d i t i o n s such

ies. with

these

as C a F

having

2

a low m e l t i n g

Afanasyev 3

c r u c i b l e s and poured

i s made t o r e f r a c t o r y w e a r a p a r t

crucibles.

Although

values are not given

slags

having melted

either a f t e r or before the

from

over the metal,

severe

i n large

The s l a g s were

i n t h e c r u c i b l e a n d g o o d d e - S was o b s e r v e d .

happened causing

point,

e t a l . (58) t r i e d

C a O / S i 0,,/Al 0 w.i t h 1 ow F e O c o n t e n t s ,

t h e s l a g was p o u r e d

n o t be

v a r i o u s t r i a l s w e r e made

points o f ~1500°C o r 2000°C.

in g r a p h i t e

and w i l l

m u s t be i n t r o d u c e d

difficulties,

2

(57), t h i s

a f l u x i n g e f f e c t on t h e r e f r a c t o r -

siag-desulphurization.

melting

metal

thereby

Despite

in the system

induc-

of using a

i s n o t a common i n d u s t r i a l p r a c t i c e a t p r e s e n t

quantities,

by

i f i t does n o t have a very low

plasma t o r c h t o keep t h e s l a g molten

considered

joints.

and the s l a g i s c o n s t a n t l y r a d i a t i n g t o the f r e e -

i t is likely

melting

they

of the slag

movable vacuum

since only e l e c t r i c conductors

tion heating board,

through

c a n be

unlikely that

s u r v i v e t e c h n i c a l problems as t h e removal

handling tool introduced

chamber.

observations

considerable

No

reference

t h a t when foaming

i n c r u s t a t i o n s in the walls o f the

t h e s l a g s were a n a l y s e d

a f t e r usev t h e

b u t one can a n t i c i p a t e s i l i c a

reduction

22 w i t h CO one

formation

( e s p e c i a l l y in the h i g h e r carbon

o f the main causes

improved

of foaming.

The

de-S

as

r e s u l t s are

f o r a l l C c o n t e n t s , as c o m p a r e d t o a t m o s p h e r i c

p r e s s u r e de-S,

but the most s i g n i f i c a n t

improvement i s

i n t h e low C ( 0 . 0 3 5 % ) s t e e l , p r o b a b l y

due

FeO

Polyakov

content a c h i e v a b l e under

vacuum.

2

sulphur content

and

concluded

power.

cases.

Volkov

e t a l . (61)

2

3

(59)

slags

on

is only

2

L i n c h e v i s k i i (60)

i n v e s t i g a t e d the use o f both o f CaO/CaF s i u r r i e s p a i n t e d to the w a l l s and

lower

et a l .

t h a t the e f f e c t o f C a F

o f f l u x i n g , h a v i n g no d e - S

found

t o t h e much

i n v e s t i g a t e d the e f f e c t of v a r i o u s C a F / C a O / A T 0

one

melts)

2

mixtures

achieved

and

good de-S

studied various mixtures

of in

CaO both

of

CaO/

C a F , C a O / A l 0 / C a F , C a O / C a F / S i 0 , p l a c e d on t h e b o t t o m

of

the c r u c i b l e .

CaO/

2

10% C a F

2

2

3

2

The

mixture

2

2

b e s t r e s u l t s w e r e a c h i e v e d w i t h a 9.0%

p l a c e d on t h e b o t t o m

of the c r u c i b l e t h a t

would, a f t e r the m e l t i n g p r o c e s s , s i n t e r to the bottom c r u c i b l e , being cleaned a f t e r the pouring. authors

do a d m i t

t h a t t h e u s e o f s l a g s may

of

In t h i s w o r k form

the the

a c c r e t i o n s on

the c r u c i b l e w a l l s , reducing i t s l i f e . S c h l a t t e r e t a l . (62) p a t e n t e d Ca0/CaF

2

o r o t h e r f l u x e s and

having

lower m e l t i n g p o i n t than

T h e i r t r i a l s were p e r f o r m e d Magnel) c r u c i b l e s . erosion critical

Although

the use of m i x t u r e s

a reducing agent, the metal

being

in Magnesia/Spinel

e i t h e r C or

in this

REM,

produced. (possibly

t h e r e i s no r e f e r e n c e t o b r i c k

in the p a t e n t , the c o n t r o l of the s l a g c o m p o s i t i o n (53)

of

respect.

is

23 In a s o m e w h a t d i f f e r e n t a p p r o a c h employed fused deoxidation

l i m e c r u c i b l e s , a ch i e v i n g ex ce 11 en t

by s i l i c o n

(due

i n the r e f r a c t o r y ) and c o o l i n g and crucible in

Strushchenko

to the

lowered

h e a t i n g t o room t e m p e r a t u r e .

( 2 0 k g ) was

of

SiO^

8 cycles

However the

of

small

f i r e d at 2000°C Which i s not f e a s i b l e

larger scale operations.

hydration • problems,

de-S,

activity

r e s i s t a n c e t o more t h a n

(35)

One

should the

has

a l s o to c o n s i d e r

furnace

the

chamber need to

be

opened f o r r e p a i r s . Several the

literature

r e p o r t s o f de-S (63, 64,

65).

with Small

REM

i n VIM

problems with

able Rare E a r t h Metal

recovery,

melts

of " o x i d e - l i k e " slags

(56), formation

p e r s i s t , but the main problem costumers. -

carry-over to

i s one

exceed

found

unpredict-

(63), etc., by

T h i s i s b e c a u s e t h e e x a c t e f f e c t s o f REM

of d e l e t e r i o u s RE-Fe phase

certain

limits.

except

in

subsequent

of acceptance

to s u p e r a l l o y s are not w e l l u n d e r s t o o d , formation

are

f o r the

( 6 4 ) when t h e s e

still

the addition known additions

24

1.3

O b j e c t i v e s o f the Research

Project

S i n c e i t i s w e l l e s t a b l i s h e d t h a t i n VIM

furnaces

u s i n g b r i c k - m o r t a r l i n i n g s t h e w e a r i s l o c a l i z e d on t h e mortar

joints

(50,66),

mortar

( o r c e m e n t s ) by s t e e l s a n d / o r

most i m p o r t a n t

i t was d e c i d e d t h a t t h e a t t a c k o f

p o i n t t o be s t u d i e d .

s u p e r a l l o y s was t h e T h i s s t u d y was t o

e n c o m p a s s b o t h t h e a t t a c k m e c h a n i s m s a n d some r o u g h e s t i m a t i o n of the r e a c t i o n r a t e s , although

no a t t e m p t

e x a c t k i n e t i c s was t o be m a d e .

In a d d i t i o n , a t t e m p t s

be made t o d e v e l o p order t o improve

a cement w i t h o u t

low s t a b i l i t y

the overall lining

performance.

F i n a l l y , samples analysed and

to derive the

o f used

oxides, in

V I M r e f r a c t o r i e s w e r e t o be

and c o r r e l a t i o n s attempted

between these

observations

the test r e s u l t s , in order to verify the v a l i d i t y

experimental

findings.

were t o

of the

25

CHAPTER 2 EXPERIMENTAL In

order to study the attack o f mortar

we p r o p o s e d ,

d i f f e r e n t t e c h n i q u e s were c o n s i d e r e d .

w e t t i n g s t u d i e s ( s u c h as s e s s i l e d r o p s ) to

b y m e t a l s , as

p r e d i c t the s t a b i l i t y

have been

and r e a c t i o n o f metals

Although extended

with

ceramic

substrates

( S u t t o n ' s ( 1 9 ) , f o r i n s t a n c e ) i t was f e l t

they would

not, in a l lcases, simulate exactly or closely

e n o u g h t h e c o n d i t i o n s o f VIM. cases r e a c t i o n products which d r o p l e t may be f o r m e d

This a r i s e s because

that

i n some

limit the spreading of the

(67) and t h e chemical

composition

of

t h e d r o p l e t may be s u b s t a n t i a l l y a l t e r e d i n a r e a s o n a b l y experiment.

T h i s e f f e c t has been

where t h e r e a c t i o n o f carbon refractories volume r a t i o s

i s concerned

long

noti ced parti cul arly i n cases

i n the metal with the oxide

due t o t h e v e r y h i g h i n t e r f a c e /

(both metal/ceramic

and metal/vacuum).

In

a d d i t i o n i t was d e s i r e d t o a c q u i r e s u f f i c i e n t k n o w l e d g e o f the o r d e r o f magnitude element

losses and/or

estimated in a real

o f t h e r e a c t i o n r a t e s so t h a t oxygen

pick-up

furnace based

alloying

( i f a n y ) c o u l d be

on t h e d a t a g e n e r a t e d .

a l a s t f a c t o r i t was f e l t t h a t w e t t a b i l i t y t e s t s w o u l d

As over-

emphasize

small variations in surface finish.

Since the

materials

used were e i t h e r commercial

used

products

in real

furnaces or experimental

c o m p o s i t i o n s , they would n e c e s s a r i l y

vary s l i g h t l y i n surface

finish.

26

In crucibles of metal time.

order then

t o s i m u l a t e t h e VIM p r o c e s s ,

as shown i n F i g . 3 were p r o d u c e d , were melted

under

ment o f t h e e x p e r i m e n t a l once,

and no a t t e m p t

quent

heats

of the size

s e t - u p , each

length of

and t h e arrange-

crucible

in a crucible.

was u s e d

only

I t was r e a l i z e d t h a t t h e s u r f a c e /

c r u c i b l e was o b v i o u s l y q u i t e

a s m a l l VIM f u r n a c e ; h o w e v e r , t h i s

experimental

amounts

was made t o s t u d y t h e e f f e c t o f s u b s e -

volume r a t i o i n t h i s to even

and fixed

vacuum, f o r a c e r t a i n

As a n a t u r a l c o n s e q u e n c e

small

case, l a r g e r than

dissimilar

ratio i s , in the

in the actual

case.

Conse-

quently a magnification of the reaction

effects

hence i m p r o v i n g

the a b i l i t y

to assess the s t a b i l i t y

of r e f r a c t o r i e s

i n contact with melts

of the test

e f f e c t p r e s e n t was p o s s i b i 1 i t y by t h e m e t a l , w o u l d

cause

under

i s observed,

vacuum.

Another

that wetting of the crucible

variations

in t h e m e t a l / r e f r a c t o r y i n t e r f a c e s ,

i n t h e vacuum/metal and as shown i n F i g . 4 .

felt,

however, that since these wetting c h a r a c t e r i s t i c s

quite

r e p r o d u c i b l e f o r each

cause

a significant variation

The

of the

in interfacial

refractories

apparatus

under

distance

through

The

a Pyrex

from the metal

order to calibrate pyrometer

area that

glass,

vacuum. The temper-

a narrow-angle

infrared

placed at a s u f f i c i e n t

to minimize

condensation

f o r emi s s i v i t i e s ,

directly controlled

they

of the relative

e m p l o y e d i s shown i n F i g . 5 .

a t u r e m e a s u r e m e n t s w e r e made w i t h pyrometer

were

meta 1/re f rac to ry p a i r and d i d n o t

c o u l d be a s s u m e d n o t t o a l t e r t h e p l a c e m e n t stabilities

I t was

pure

on i t . I n

Fe a n d N i w e r e

t h e power supply

and a

used.

27 v a r i a t i o n w i t h i n + 5°C o f the s p e c i f i e d t e m p e r a t u r e typical. r a t e was

T h e p r e s s u r e was

always

v e r i f i e d before each

was

k e p t b e l o w 30y and t h e l e a k

run.

The c o m p o s i t i o n s o f t h e m a t e r i a l s u s e d f o r t h e

tests

a r e g i v e n i n T a b l e s 5 and 6 and e x c e p t where n o t e d , t h e y a r e nominal

c o m p o s i t i o n s g i v e n by t h e The m e t a l l i c s a m p l e s

with steel

o r 13.5g

A typical ambient

suppliers.

weighed

tests

+ O.lg f o r the t e s t s with s u p e r a l l o y s .

melt c y c l e would

temperature

lOg + O.lg f o r the

f o r complete

a s h o r t h o l d i n g time at around s u p e r h e a t i n g to 1520°C

i n v o l v e slow h e a t i n g from

o u t g a s s i n g of the

crucible,

1000°C, m e l t i n g the

( i n t h e c a s e o f 1095

sample,

s t e e l ) or to

( i n the case o f N i c k e l v a c X-750) , h o l d i n g a t t h a t

1500°C

temperature

f o r the d e s i r e d p e r i o d o f t i m e , t u r n i n g o f f the power s u p p l y and c o o l i n g to ambient

temperature

under vacuum.

This

was

done i n o r d e r to m i n i m i z e the c h a n c e s o f o x i d a t i o n o f the metallic

sample. The c r u c i b l e s were p r o d u c e d i n a p a p e r m o u l d w i t h a

p a r a f f i n wax temperature

core.

After drying (or s e t t i n g ) at

ambient

they were e i t h e r f i r e d a t the r e q u i r e d t e m p e r a t u r e

(in a g a s - f i r e d f u r n a c e ) or h e a t e d to a t e m p e r a t u r e range of 600°-700°C

in the

to burn t h e p a p e r and t h e p a r a f f i n

wax

and t h o r o u g h l y d r y them. Metal

samples

f o r c h e m i c a l a n a l y s i s were s e p a r a t e d

from the c r u c i b l e s , c a r e f u l l y c l e a n e d of r e f r a c t o r y tions, filed

incrusta-

to e l i m i n a t e open p o r o s i t y and then c u t i n s m a l l

pieces for analysis.

The c a r b o n and o x y g e n

a n a l y s e s w e r e made

28

by t h e c o n v e n t i o n a l t e c h n i q u e s i n L E C O a n a l y s e r s . In o r d e r t o o b s e r v e t h e r e f r a c t o r y - m e t a l i n t e r f a c e s or o t h e r r e f r a c t o r y samples the specimens or removing

without s e p a r a t i n g the metal grains of the ceramic.

t h i s , the samples under

i t was n e c e s s a r y t o c u t a n d

vacuum.

were i m p r e g n a t e d

w i t h 1 ow-vi s cos i t y epoxy, meta11ographic

to l y diamond p a s t e , they were

e i t h e r i n an O p t i c a l

observed

Microscope or in a Scanning Electron

M i c r o s c o p e e q u i p p e d w i t h an X - R a y E n e r g y some

from the ceramic

In o r d e r t o a c c o m p l i s h

A f t e r p o l i s h i n g by s t a n d a r d

t e c h n i q u e s , down

polish

cases the microprobe

was a l s o

used.

Spectrometer.

In

29

CHAPTER 3 RESULTS S i n c e t h e t e s t s made w i t h s t e e l s a n d w i t h s u p e r a l l o y s are a n a l y s e d i n d i f f e r e n t w a y s , as d i s c u s s e d b e l o w , section will

this

be d i v i d e d a c c o r d i n g t o t h e a l l o y u s e d f o r t h e

tests. 3.1

T e s t s Using AISI In

1095 S t e e l

order to avoid problems with variation

and oxygen c o n t e n t and a c t i v i t y ensure

o f carbon

over a wide range,

and t o

r e a c h i n g t h e s t e a d y s t a t e d e s c r i b e d by M a c h l i n , a

high-carbon

s t e e l was s e l e c t e d f o r t h e s e t e s t s .

Although

c a r b o n was t h e e l e m e n t t o be s t u d i e d , t h e i n t e r e s t was i n steel

i n t e r a c t i o n w i t h r e f r a c t o r i e s and so a p l a i n

commercial in

s t e e l was s e l e c t e d .

this steel

2 hours,

consumption

under vacuum.

Tasil

Although

X — ( M u l ' l i t e Based

initial

The t e s t s

content.

Cement)

t h i s p r o d u c t i s n o t d e s i g n e d t o be u s e d i n

contact with metal

i n a VIM f u r n a c e b u t r a t h e r as a

support f o r the coils composition

content

f o r v a r i o u s l e n g t h s o f time, from 5 minutes t o

and t h e m e t a l was a n a l y s e d f o r c a r b o n

3.1.1

oxygen

(due t o the high C content) minimizes

v a r i a t i o n s i n carbon were c o n d u c t e d

The low i n i t i a l

carbon

and t h e l i n i n g i t s e l f ,

makes i t p a r t i c u l a r l y

mechanical

i t smullite

interesting since i t enables

30 one

t oanalyse

silica

the behaviour

activity

refractory mullite silica

to the

in the b i n a r y S i O g / A ^ O ^ j w i d e l y

industry.

composition content

corresponding

Any

minimum used

in

cement w i t h h i g h e r alumina

s h o u l d be designed

in a m u l l i t e form,

the

than

the

s o as to have a l l i t s

to minimize

the

silica

activity. Fig.

6 presents -

(C.

the v a r i a t i o n of carbon

Cp. .• ,) a f t e r m e l t i n g i n T a s i l

initial

very high consumption

is r e a d i l y apparent.

c r u c i b l e s (Alundum

of carbon

The

and

parabolic relationship indicates

of

the m e t a l / r e f r a c t o r y i n t e r f a c e a f t e r a short

(5 m i n s . ) F i g . 7 , o n e

silica

can

s e e how t h e m u l l i t e i s d e p l e t e d

a t t h e i n t e r f a c e and

remaining

i s the d i f f u s i o n o f

oxygen.

Observing time

1139).

b y the m u l l i t e r e f r a c t o r y

that the c o n t r o l l i n g step in the process s i l i con

Xcrucibles,

Tina I

compared with m e l t i n g in alumina The

content

how t h e a l u m i n a

particles

have a h i g h e r s p e c i f i c a r e a , f u r t h e r e n h a n c i n g

dissolution

of the r e f r a c t o r y .

I f one

c a l c u l a t e s the

in e q u i l i b r i u m w i t h pure Rosenqvist

the

(68) 3 A 1

activity

alumina,

of s i l i c a

using the data

from

f o r the r e a c t i o n 2°3

+

2 S i 0

2

=

3 A 1

2°3 *

2 s i 0 2

A G

a v a l u e o f 0.45

in m u l l i t e ,

is obtained.

i n e q u i 1 i b r i urn w i t h p u r e u s i n g the e q u i l i b r i u m

(Mullite) 1600°C

=

6000C

- a~\

C a l c u l a t i n g t h e p r e s s u r e o f CO

silica

or with s i l i c a

at this

activity

31 S

one

+ 2_C = 2 CO + SJ_

2

finds P

and hence in

i 0"

mullite

n

cases s i l i c a

of carbon

the a c t i v i t y

under

will

be e x t r e m e l y

by t h e m u l l i t e f o r m a t i o n i s

to the i n c r e a s e i n carbon

d e p r e s s i n g t h e CO

unstable

vacuum, i . e . , the l o w e r i n g i n

of s i 1ica caused

not comparable

3.1.2

a

c 0

in both

presence

-. ^ S i O ? = 0.67 p 2

C 0

activity

caused

pressure.

Cements with

10% S i 0

( T a y l o r 320,

2

Alundum

F o l l o w i n g the t e s t s with the m u l l i t e based lower

silica

cements were t e s t e d , i n o r d e r to

whether or not they would

1162)

cement,

determine

be m o r e i m m u n e t o a t t a c k by t h e

T h i s c o u l d h a p p e n due t o t h e l o w e r e x p o s e d s t a b i l i t y phase

by

( m u l l i t e or s i l i c a

area of the

steel.

low-

r i c h compound, s i n c e in

some c a s e s , o t h e r f l u x e s , s u c h a s A l k a l i n e o x i d e s w e r e p r e s e n t ) . In observed.

a l l c a s e s e x t e n s i v e w e t t i n g o f t h e c r u c i b l e was When T a y l o r 320 was

used a f t e r d r y i n g a t

( s i n c e i t i s r e c o m m e n d e d t h a t i t be u s e d w i t h o u t voilent boil crucible. carbon

firing),

a

out of

the

o c c u r r e d , t h r o w i n g most o f the metal

When t h e s e s a m p l e s

consumption

were a n a l y s e d , t h e y

o f up t o 0 . 1 %

in 5 minutes.

600°C

showed

Since

the

c r u c i b l e s w e r e c e r t a i n l y w e l l d r i e d ( n o t o n l y due

to the

600°C

d r y i n g but a l s o because

vacuum

before

melt-down),

f i r i n g was

of the slow h e a t i n g under attempted

t h a t the most s t a b l e s i l i c a The metal carbon

did not boil

consumptions

w i t h the aim o f making

c o n t a i n i n g phases

would

be

in the f i r e d c r u c i b l e s , a l t h o u g h

were s t i l l

high, being of the order

sure formed. the of

32 0.2%

i n 30 m i n .

refractories

X-Ray d i f f r a c t i o n

on p o w d e r o f

both

r e v e a l e d a low i n t e n s i t y s e t o f q u a r t z p e a k s i n

the u n f i r e d sample, while lower

analyses

the f i r e d sample presented

a much

i n t e n s i t y s e t o f q u a r t z p e a k s as w e l l as p e a k s

sodium-potassium h o w e v e r , was

a1umino-si1icates.

of

The most d r a m a t i c

in the p h y s i c a l appearance

change,

of the c r u c i b l e s , with

t h e f i r i n g b r i n g i n g an e x t e n s i v e d e n s i f i c a t i o n o f t h e s t r u c t u r e , p a r t i c u l a r l y a t t h e s u r f a c e , a s s h o w n i n F i g . 8. probably

T h i s would

be r e s p o n s i b l e f o r t h e h i g h e r s t a b i l i t y

in the

fired

c o n d i t i on . When one crucible

observes

( F i g . 9) o n e

in s i l i c a

caused

notices a reasonably

by t h e d i f f u s i o n

less s t a b l e component. the high alumina

i n f e r i o r mechanical e a r l y , maybe even

d e n s i t y than to suppose

of

this

Fig. 9 that

had t h e

binding

which

l a y e r has

probably

break

a much

o f f very

d u r i n g the s h r i n k i n g or the c l e a n i n g of

the

furnace.

C e m e n t s P r o d u c e d Us'i n-g F l u o r i d e s

Since the t e s t s with s i l i c a the inadequacy

of s i l i c a carbon

Magnesia

b e a r i n g cements

as a f l u x f o r u s e

s t e e l , i t was

a d d i t i o n s to a l u m i n a spine1-bonded

2

the bulk of the r e f r a c -

that this

s t r e n g t h and w i l l

i n an a c t u a l

contact with

from

region between the g r a i n s

It i s reasonable

3.1.3

decomposition

It i s also obvious

r e s u l t e d i n a much l o w e r

skull,

and

Si0

thick layer depleted

layer depleted in silica'has

phase removed from the

tory.

the a l t e r e d l a y e r o f a 10%

under

revealed

vacuum i n

decided to t r y d i f f e r e n t

in order to promote i t s r e a c t i o n with b r i c k (Magnel) used i n

VIM.

the

33

I t i s known- t h a t f l u o r i d e s a r e v e r y good f l u x e s f o r t h i s system and

(and f o r that matter,

f o r almost

any oxide

system)

t h e y h a v e b e e n u s e d i n many c a s e s t o p r o m o t e r e a c t i o n i n

refractory production (69, 70). effective

Although

i n t h i s t h e y p r e s e n t some l i m i t a t i o n s s u c h a s

e x c e s s i v e a t t a c k on t h e r e f r a c t o r i e s of c l i n k e r ) (69), a decrease alumina

they are very .

(during the production

in sintering

sintering) (70), the possibility

ability of health

(since water soluble f l u o r i d e s are hazardous) flouride emissions

( i n pure hazards

and p o s s i b l e

d u r i n g f i r i n g . \ However, t h e two

first

l i m i t a t i o n s are a c t u a l l y advantages i n the case o f t h e i r utilization and

i n a cement, i . e . , r e a c t i o n with the r e f r a c t o r i e s

c o n t r o l l e d sintering, in order to achieve a r e l a t i v e l y

porous

product with

little

dimensional

change.

p r o b l e m s may i n d e e d p r e s e n t d i f f i c u l t i e s

T h e two o t h e r

i f not dealt with

care fu 1 l y . The

s e l e c t i o n of a non-water soluble f l u o r i d e , at a

reasonable price, Li

fluorides.

percentage

l i m i t s o u r c h o i c e e s s e n t i a l l y t o C a , Mg a n d

With r e s p e c t to the f l u o r i d e e m i s s i o n s , i f the

of fluoride

i n the cement i s kept at a reasonable

l e v e l , and the amount o f cement m i n i m i z e d , VIM

as p r a c t i c e d i n

o p e r a t i o n s , one s h o u l d n o t e x p e c t a h i g h c o n c e n t r a t i o n o f

fluoride emissions

during the f i r i n g o f the c r u c i b l e .

Due t o i t s r e a d y a v a i l a b i l i t y , c a l c i u m f l u o r i d e selected f o r the i n i t i a l

tests.

was

In o r d e r t o e n s u r e t h e

p o s s i b i l i t y o f f l u x i n g , some c a l c i u m o x i d e was a l s o a d d e d , with the aim o f reaching the t e r n a r y e u t e c t i c at approximately

34 4% C a O / 7 2 % C a F / 2 4 % ' A l g O g .

Of c o u r s e a l l the

2

t e s t e d were s a t u r a t e d w i t h a l u m i n a , the t e s t s b e i n g 82% A l 0 / 1 4 % 2

u s e d was 1139,

the f i n a l

C a F / 4 % CaO

3

A l l the samples

and

were f i r e d

in a g a s - f i red f u r n a c e f o l l o w i n g which composed of ca1ciurn a 1uminates m i c r o s t r u c t u r e shown i n F i g . No spectrum.

f o r m a b i l i t y to

f o r two

hours

they were

o r CA

3

The

1300°C

typical

were p r e s e n t i n the

and,

2

X-Ray

peaks

could

i n some c a s e s C A g .

Only

2 8 % a n d t h e c a l c i u m o x i d e t o 8% c o u l d some be o b s e r v e d .

at mainly

i n c a s e s when t h e a m o u n t o f c a l c i u m f l u o r i d e was

C^A^

the

10.

In a l l c a s e s , t h e c a l c i u m a l u m i n a t e as C A,_

in

alumina

and a l u m i n a , w i t h the

c a l c i u m f l u o r i d e peaks

be i d e n t i f i e d

used

c a s t a b l e cement Alundum

in order to impart p l a s t i c i t y

mixture.

one

where the

2

a c t u a l l y the high alumina

compositions

i n c r e a s e d to

low-melting

p r o d u c t i o n of the c a l c i u m

aluminates

is a t t r i b u t e d to the c o n v e r s i o n of the c a l c i u m f l u o r i d e c a l c i u m o x i d e by one 3CaF CaF

2

of the f o l l o w i n g r e a c t i o n s :

+ Al 0

2

2

+ H0 2

3

= 2A1F

= 2HF

+

+ 3CaO

3

CaO

In o r d e r t o t e s t t h e a d e q u a c y adherence

t e s t s and s t a b i l i t y

d i s p l a y s the r e s u l t s

into

of this material

t e s t s were p e r f o r m e d .

of the adherence

tests.

The

F i g . 11 reaction of

t h e c e m e n t a n d t h e b r i c k i s e v i d e n c e d n o t o n l y by t h e p h y s i c a l o b s e r v a t i o n o f t h e i n t e r f a c e b u t a l s o by t h e c h e m i c a l tion profile. almost

One

should also expect this behaviour

a n y b r i c k , a g a i n due

f1uoride

employed.

to the high f l u x i n g

composiwith

a b i l i t y of the

35 The alumina

same s e r i e s o f s t a b i l i t y

cement A l u n d u m 1139.

t e s t s was

Comparing

performed

F i g s . 12 a n d

13

can see t h a t t h e r e i s no s i g n i f i c a n t d i f f e r e n c e i n consumption

with e i t h e r of the cements,

cement does

not have lower s t a b i l i t y

alumina

with one

carbon

indicating that

than

the

the

original

cement used to produce i t . To f u r t h e r i n v e s t i g a t e t h e p o s s i b i l i t i e s

f 1 u o r i d e - m i n e r a 1 i z e d cements,

of the

i t was

d e c i d e d t o t r y MgF^,

with

the aim o f p r o d u c i n g m a g n e s i a - a l u m i n a

spinel, instead of

calcium-aluminates. F i n e l y ground 1139

MgF^

a n d MgO

were mixed

i n the p r o p o r t i o n s 85% A l 0 / 1 4 % 2

f i r e d at 1300°C, the f l u o r i d e .

i.e., slightly

The

mechanical

MgF /l%

3

MgO

2

Alundum (SP2)

p r o p e r t i e s o b t a i n e d w e r e much and o f t h e c a l c i u m - f l u o r i d e

F i g . 14 s h o w s t h e m i c r o s t r u c t u r e o f

produced.

original

cement) while the i n t e r g r a n u 1 ar m a t e r i a l i s a

alumina

and a l u m i n a .

were

a r e as good

mixture only

consumption

tests

as t h e v a l u e s f o r p u r e

cement, w i t h i n the e x p e r i m e n t a l v a r i a t i o n s . It i s c l e a r then

f a v o u r a b l e f o r use

under

that this VIM

In o r d e r t o i m p r o v e lignin

the

present.

15 s h o w s t h e r e s u l t s o f c a r b o n

in t h i s m a t e r i a l , which

(from

In t h e X - R a y p o w d e r d i f f r a c t i o n ,

and s p i n e l peaks Fig.

alumina

l a r g e g r a i n s are Al^O^

the

material

of spinel

The

and

above the m e l t i n g p o i n t of

s u p e r i o r t o t h o s e o f A l u n d u m 1139 cement (CAF).

with

s u l p h i t e was

added

composition would

be h i g h l y

conditions (at least for steels). its plasticity

and c o l d

as a 1 0 % s o l u t i o n i n w a t e r ,

adherence, mixed

36 with the cement powders. excellent results. was

The

cold adherence

In m o s t t e s t s t h e b r i c k / m o r t a r i n t e r f a c e

s t r o n g e r than the mortar

f i r e d m a t e r i a l was

i t s e l f , and

the s t r u c t u r e of the

n o t a l t e r e d by t h i s a d d i t i o n .

Observing

the f i r e d

i n t e r f a c e , i t was

t h i s cement r e a c t s with the spinel, phase phase

t e s t s gave

noticed that

and w i t h t h e

binding

o f t h e p e r i c l a s e g r a i n s i n t h e Magnel b r i c k , and

t o a l e s s e r e x t e n t w i t h t h e MgO the r e s u l t s

itself

( F i g . 16).

and c a l c i u m a l u r n i n a t e s , M g F

2

MgO

and s p i n e l w i t h t h e e x c e s s

alumina)

producing highly reactive i t was

decided that,

i n o r d e r t o p r o m o t e m o r e r e a c t i o n w i t h t h e MgO

particles,

A l F ^ s h o u l d be u s e d t o f o r m s p i n e l w i t h t h e MgO T h i s c o u l d be d o n e i n two w a y s :

the Al 0 /MgF /MgO mixture 2

3

2

percentage and A 1 0 2

3

Analysing

a c h i e v e d p r e v i o u s l y (CaF^ p r o d u c i n g h i g h l y r e a c t i v e

CaO

Magnel.

reacts

and

The

By a d d i n g

used, mixed

f o r m e r was

b e t w e e n Magnel: b r i c k s .

lignin

mixture

s u l p h i t e s o l u t i o n and

A g a i n , the c o l d s t r e n g t h and

i t y were v e r y good, i n d i c a t i n g t h a t cements w i t h o u t achieve these p r o p e r t i e s .

The

to the s h o r t r e a c t i o n time

The with alumina

Low

Silica

given to both

Phosphate

Bonded

samples

cements,

was spread

silica

can

however,

probably

due

(2 h r s . ) .

Cement

o t h e r component e x t e n s i v e l y used i n to produce

3

plastic-

binding characteristics

d i d i n o t d i f f e r s u b s t a n t i a l l y from t h o s e o f SP2,

3.1.4

2

s e l e c t e d as b e i n g e a s i e r

3

w i t h t h e 10%

A1 0

based m i x t u r e , w i t h Al

t o do a n d a 7 0 % A l 0 / 1 6 % A l F g / 1 3 % "MgF^/1% MgO 2

from

A l t o

r e d u c i n g the i n i t i a l

o r , by d e s i g n i n g an MgO additions.

grains

connection

is phosphoric acid with

or

37 without s i l i c a .

In o r d e r t o i n v e s t i g a t e t h e b e h a v i o u r o f t h e

p h o s p h a t e b o n d , t e s t s w e r e p e r f o r m e d w i t h T a y l o r 341 It

cement.

i s b e l i e v e d that in a phosphate bonded alumina

m i x t u r e , A1H ^ ( P O ^ ) ^ • 3 ^ 0 ,

the hydrated aluminum-phosphate

phase i s the major phase produced i n the b i n d e r system and, upon

firing,

aluminum

orthophosphate (AlPO^), which in i s o -

s t r u c t u r a l w i t h s i l i c a , w o u l d be p r e s e n t .

The o r t h o p h o s p h a t e

is b e l i e v e d to decompose

reaction

a c c o r d i n g t o the

2 A 1 P 0 .4 = A 1 ,do0 , + P CL. do 0

f o r m i n g A I Z C uo w i t h t n e v o l a t i l i z a t i o n 0

agreement, however,

o f P J2 r .5

T h e r e i s no

c o n c e r n i n g the exact temperature of the

d e c o m p o s i t i o n , K h o r o s h a v i n , e t a l (72) r e p o r t i n g i t s s t a r t at to,

1 4 6 0 - 1 4 8 0 ° C and O'Hara e t a l (71) s t a t i n g t h a t i t i s s t a b l e at l e a s t , 1760°C.

I t i s c l e a r however, that since

i s an o x i d e e v e n l e s s s t a b l e t h a n S i O ^ ( for

P2U,-,"as

compared

process in question partial of

A G

ig73K

=

P °5 2

"55KCa1/mol0

t o - 1 2 5 K C a l / m o l 0^ f o r S i C ^ ) a n d a s t h e

i s t o o c c u r u n d e r vacuum

p r e s s u r e o f ^2^5'

o n e

S n

(and hence

low

° u l d expect the decomposition

t h e b o n d t o be e n h a n c e d u n d e r v a c u u m

induction melting

of

stee1 . Fig. crucibles.

17 s h o w s t h e c a r b o n c o n s u m p t i o n i n T a y l o r

One c a n s e e t h a t a l t h o u g h t h e y a r e h i g h e r t h a n

those i n the A l u m i n a cement Alundum not of

341

pronounced.

The main

1139, the d i f f e r e n c e i s

reasons f o r the acceptable b e h a v i o r

t h i s c e m e n t a r e t o be f o u n d i n i t s r e l a t i v e l y

c o n t e n t , t h e a b s e n c e o f SiO^

low

and i t s e x c e l l e n t g r a i n

s u r f a c e q u a l i t y and s t r e n g t h as c o m p a r e d

?2®5

sizing,

to the c o r r e s p o n d i n g

2

38 p r o p e r t i e s o f Alundum 1139. interface

f o r a 15 m i n u t e

Observing the m e t a l / r e f r a c t o r y steel-test in this material (Fig.

1 8 ) , one n o t i c e s no a l t e r a t i o n Although

in the s t r u c t u r e of the

some g r a i n s c a n be s e e n

and a d e p l e t i o n i n p h o s p h o r o u s

cement.

t o be g o i n g i n t o t h e

melt

c a n be n o t i c e d c l o s e t o

the

i n t e r f a c e , t h i s seems to have l i t t l e

o r n o e f f e c t on

the

strength of the m a t e r i a l . 3.1.5

Silica

C o n t a i n i n g Phosphate

Bonded

T h e m o s t w i d e l y u s e d c e m e n t i n VIM Coralbond,

a silica

c o n t a i n i n g phosphate

addition of s i l i c a

and P 0 o

c

f o r m an e u t e c t i c a t 9 0 0 ° C ,

b

c

e u t e c t i c in the high alumina at

1200°C.

Indeed,

p l a s t i c , adherent good

furnaces is

bonded cement.

i s p r o b a b l y made t o i m p r o v e

c o l d s t r e n g t h and to e n h a n c e i t s f l u x i n g

one

cold strength.

any

I t i s hence

The

plasticity,

ability, since

while the lowest

side of the A l f t ^ ^ t ^ ^

observes

to almost

Cement

melting binary is

t h a t t h i s cement i s s u r f a c e , and

silica

extremely

develops

a very

a very d e s i r a b l e cement,

from

t h e s t a n d p o i n t o f i t s a c t u a l u t i l i z a t i o n b y b r i c k l a y e r s on

the

s h o p f l.oor. I t m u s t be k e p t i n m i n d , h o w e v e r , t h a t a l t h o u g h p r o p e r t i e s are important p r o p e r t i e s t o be t a k e n

these

(and a r e , i n s e v e r a l c a s e s , the

i n a c c o u n t when s e l e c t i n g a

mortar)

they are not the only important p r o p e r t i e s of a mortar. t h e c a s e o f VIM

or other processes

i s i m p o r t a n t , one of

in which

should look i n i t i a l l y

In

refractory attack

at the c o m p a t i b i l i t y

the mortar with the c o n d i t i o n s of the process.

case, c o m p a t i b i l i t y with high carbon

only

In

our

a c t i v i t y or very

low

39 oxygen a c t i v i t y metals

under

this

can one

c o n d i t i o n i s met,

application properties final

vacuum i s e s s e n t i a l .

and s t r e n g t h o f a j o i n t b e f o r e f i r i n g . i n t h e c a s e o f VIM

after

proceed to t e s t the ease

I n o t h e r w o r d s , i t may

of

These

a r e n o t as i m p o r t a n t as

q u a l i t y of the m a t e r i a l produced

lining.

Only

and the l i f e

the

of the

pay t o use a cement t h a t w i l l

n o t be a s e a s y t o t r o w e l l o r t o s p r e a d , a n d w i l l

not

produce

as s t r o n g a c o l d j o i n t - - i n o r d e r t o a c h i e v e l o n g e r l i n i n g

life

and b e t t e r m a t e r i a l q u a l i t y . In

a l l steel

tests with Coralbond, although the

w e r e w e l l d r i e d a n d p r e f i r e d a t 900-°G v a r i o u s d e g r e e s b o i l i n g were o b s e r v e d , i n d i c a t i n g interaction. tion

is

f o r carbon

i n C o r a l b o n d as a f u n c t i o n o f t h e s q u a r e

good s t r a i g h t - l i n e

(mullite

consump-

root of time,

cement).

The

P2O5)

i n t h e p o r e s o f t h e r e f r a c t o r y as

It i s i n t e r e s t i n g to note t h a t both

and T a s i l - X p r e s e n t t h e same d e c o m p o s i t i o n

(and

proposed

by M a s s a n d A b r a t i s ( 7 3 ) f o r t h e r e d u c t i o n o f m u l l i t e Fe-C m e l t s .

very

f i t shows t h a t i n b o t h c a s e s the r e a c t i o n

c o n t r o l l e d by d i f f u s i o n , p r o b a b l y o f S i O a n d CO^

maybe o f

of

a strong metal/refractory

F i g . 19 s h o w s t h e r e s u l t s

together with those f o r Tasil-X

samples

by

Coralbond

r a t e i n the. t e s t s

performed. When' (Fig.

Cora 1 bond/meta 1 i s observed

2 0 ) , one n o t i c e s t h e c h a r a c t e r i s t i c s i l i c a

a l s o the t o t a l to

the i n t e r f a c e

decomposition

of tne bond.

note t h a t the bond decomposes

d e p l e t i o n and

It i s interesting

(and the phosphorous

drops) at a c o n s t a n t d i s t a n c e from the working

content

f a c e ( F i g . 21)

40 while the s i l i c a

boundary i s not as linear.

This probably

s u g g e s t s t h a t the phosphate bond decomposes by thermal p r e s s u r e e f f e c t s , w i t h t h e v o l a t i I i z a t i o n o f ^2^5' interface

t n e

n

'9 t

temperature.

It i s a l s o c l e a r again in t h i s case t h a t the p e n e t r a t e s i n t o the p o r o s i t y l e f t by the reduced and

s t r a i

i n d i c a t i n g the isotherm: c o r r e s p o n d i n g t o the

decomposition

(Si02

and

P

2^5^»

anc

*

t n a t

t n e

components

a l t e r e d l a y e r has a much

d e n s i t y than the bulk o f the r e f r a c t o r y .

metal

lower

Evidence of the

cement as source of n o n - m e t a l l i c i n c l u s i o n s

(with or without

entrapped metal) is presented in Fig. 22. I t i s c l e a r from t h e s e o b s e r v a t i o n s t h a t the t i o n o f s i l i c a / p h o s p h a t e bond makes C o r a l b o n d able, as f a r as chemical s t a b i l i t y VIM

combina-

less than

i s concerned,

desir-

f o r use i n

furnaces. 3.1.6

Summary o f S t e e l T e s t s

The

very negative e f f e c t

of s i l i c a with or without

other oxides o ras a 'lower a c t i v i t y been o b s e r v e d . mullite Al

Although

unexpected,

1

form i n a compound the r e s u l t s with

the

cement seemed t o be s u p e r i o r t o t h o s e o f t h e 10%

c e m e n t - - T a y 1 o r 320.

T h i s t y p e o f b e h a v i o u r was

observed in w e t t a b i 1 i t y s t u d i e s performed (74).

has

The

SiO^/

also

by Sveshkov et a l .

reason f o r t h i s behaviour perhaps

can be f o u n d i n

the f a c t t h a t the phases p r e s e n t i n the h i g h e r alumina

cement

are not those p r e d i c t e d by e q u i l i b r i u m c o n s i d e r a t i o n s , s i n c e after firing

i t s b e h a v i o u r was

improved.

I n any e v e n t ,

cements proved u n s u i t a b l e f o r the a p p l i c a t i o n

both

in question

and

41

no f u r t h e r

i n v e s t i g a t i o n was

The

possibility

o f s i l i c a , was

promote bonding The

of using

shown, s i n c e

of the basic alumina

t h e y do n o t r e d u c e

reaction,

the corrosion

constituents

inclusions dissolved

stability do

c h a r a c t e r i s t i c s of the r e f r a c t o r i e s to the e x t e n t of the

although this factor alone

could

are

metal not

prevent

reaction.

In s e v e r a l tory

the

instead

bricks.

indeed important with respect ceramic

f l u o r i d e s as f l u x e s ,

cement e m p l o y e d i n the t e s t s and

to the

physical

undertaken.

cases the c o r r o s i o n was

observed

in the metal

to cause

w h i c h may

o r may

d u r i n g the remaining part

the s t a g e o f f o r m a t i o n and s i z e and

o f one

of the

the formation n o t be

refracof

completely

of the heat depending composition, etc.

on

42 3.2

T e s t s U s i n g X-750 S u p e r a l l o y S i n c e i t soon

became a p p a r e n t

b e t w e e n X-750 ( a n d p r o b a b l y the r e f r a c t o r i e s

under

any

t h a t the i n t e r a c t i o n s

o t h e r low-C s u p e r a l l o y )

vacuum were not enough to cause

easily

d e t e c t a b l e v a r i a t i o n i n any o f t h e a l l o y i n g

i t was

decided instead to concentrate

a l t e r a t i o n s at the meta1/refractory

elements,

interface.

In a d d i t i o n , caused

e i t h e r by t h e d i s s o l u t i o n o f r e f r a c t o r y o x i d e s o r by

Due

to the r e l a t i v e l y

t i t a n i u m and

any

a t t e n t i o n on the a c t u a l

the v a r i a t i o n of the oxygen content of the a l l o y ,

m e n t o f r e f r a c t o r y i n c l u s i o n s was

and

entrap-

to be s t u d i e d .

high percentage

of

chromium in t h i s a l l o y , a l l of which

aluminum have h i g h l y

n e g a t i v e i n t e r a c t i o n c o e f f i c i e n t s w i t h o x y g e n i n Ni a l l o y s (ej

1

= -210, e £

expect

r

= -38.6, e j

a relatively

equi1ibrium

1

= -70 a t

1873°K (75)) o n e

high oxygen content in t h i s a l l o y

with , f o r example, alumina.

This is

should

in

clearly

s h o w n i n F i g . 23, w h e r e t h e o x y g e n c o n t e n t i n e q u i l i b r i u m with alumina percentage

i s shown, f o r a N i - A l a l l o y ,

of aluminum.

lOppm oxygen range superalloys

r e a d i l y see t h a t the

are r a t h e r d i s p l a c e d from e q u i l i b r i u m and to the m e l t i n g p r a c t i c e of

d e o x i d a t i o n with carbon

time

can

usual

of values a c h i e v e d in the p r o d u c t i o n

o n l y b e o b t a i n e d due

elements

One

asa f u n c t i o n of

and t a p p i n g .

can

initial

followed bya d d i t i o n of r e a c t i v e I t i s c l e a r t h a t the

longer the

a f t e r the a d d i t i o n o f the more r e a c t i v e e l e m e n t s

and A l ) t h e c l o s e r the s y s t e m the most s t a b l e mixture

of

of

will

oxides.

approach

holding (as Ti

e q u i l i b r i u m with

43 I t m u s t be s t r e s s e d t h a t i n t h i s quite pronounced equilibria present

deviation

case t h e r e i s a

from the simple d e o x i d a t i o n

o b s e r v e d when s m a l l a m o u n t s o f d e o x i d a n t a r e

(aluminum

deoxidation of steel , for instance).

those c a s e s , the aluminum

In

c o n c e n t r a t i o n i s s m a l l , and i n

the e x p r e s s i o n f o r the a c t i v i t y

c o e f f i c i e n t of oxygen,

fo

n log fo = e°wt%0 +

I e^ w t % i

Al the term c o r r e s p o n d i n g to e ence

between

of oxygen

wt%Al

Q

t h e H e n r i an a c t i v i t y

i s also small.

The

and t h e w e i g h t

differ-

percentage

c a n be n e g l e c t e d , a s s h o w n i n F i g . 23 up t o

a p p r o x i m a t e l y 0.08% t i o n s , one

Al in N i c k e l .

In t h i s r a n g e o f

can use a r e l a t i o n s h i p o f t h e wt%0 wt%Al = Ka 3

composi-

type

2

A ]

0

or 3 l o g wt%0

+ 2 log wt%Al

= K'loga.,

n U

2 3 a n d s h o w t h a t l o g wt%,0

i s a l i n e a r f u n c t i o n of l o g wt%Al

As t h e a l u m i n u m however, h

Q

content of the a l l o y i n c r e a s e s ,

the term e'^wt%Al

d e p a r t s from wt%0, h

o

.

,

c a n n o t be n e g l e c t e d a n y m o r e

a c c o r d i n g to the

= f wt%0 o

and

relationship

. 3 2

While the r e l a t i o n s h i p

h h^^ Q

= K is still

valid

for

a f i x e d a l u m i n a a c t i v i t y , a s s h o w n by t h e e x t e n s i o n o f t h e activity

straight

not l i n e a r l y

line

i n F i g . 23, the w e i g h t p e r c e n t a g e s

r e l a t e d a n y m o r e , due t o t h e i n t e r a c t i o n

are

of the

44

two s o l u t e s i n t h e a l l o y , w h i c h simple Henrian

causes departure from

the

behaviour.

Assuming

t h a t the only s i g n i f i c a n t

i s t h a t c a u s e d b y a l u m i n u m on o x y g e n , o f t h e two e l e m e n t s

interaction

the weight

effect

percentages

c a n be r e l a t e d b y t h e f o l l o w i n g

expres-

s i on h

h

=

o Al

31og

K

a

Al 0 2

h

Q

+ 21og

A ]

=

K'

+ 3 ( l o g fo + l o g wt%0)

21og w t % A l

+ 3e^vit%M

Q

+ 31og wt%0

(1) shows t h a t l o g wt%0

function of log wt%Al Al term 3e

h

21og w t % A l

Equation

the

3

wt%Al

K'

= =

i s not a

(1)

K'

linear

, a n d c a n o n l y be a s s u m e d t o be s o w h e n

i s n e g l i g i b l e , which

only happens f o r small

c o n c e n t r a t i o n s of aluminum. I t i s t h e n o b v i o u s why

the r e f r a c t o r y / m e t a l i n t e r f a c e

becomes i m p o r t a n t i n the system, s i n c e i t w i l l thermodynamics

control

the

o f t h e p r o c e s s (by t h e compound f o r m e d ,

and

hence e x p o s e d to t h e m e t a l ) and t h e k i n e t i c s (by

i t s physical

alloy will

characteristics).

of the process,

The oxygen

content o f the

i n d i c a t e the approach o f the system to e q u i l i b r i u m ,

a n d , i f a c o n s t a n t t i m e i s t a k e n as a b a s i s f o r c o m p a r i s o n , the

most s a t i s f a c t o r y

refractory

from t h i s s t a n d p o i n t .

T a b l e 7 shows the oxygen

value found in samples

X - 7 5 0 h e l d f o r 15 m i n u t e s refractory materials.

at 1500°C

in crucibles of

It i s e v i d e n t t h a t the

of

different

refractories

45 composed o f MgO-A^O^ s p i n e l and 8 5 % A l 0 / 1 4 % z

oxygen

MgF /l%

3

and e i t h e r A l ^ O ^ o r M g O

MgO ( S P 2 ) )

2

values amongst t h e samples

(Alumina

present the lowest

f o l l o w e d b y T a y l o r 341

P e r i b o n d

b o n d e d by 4.5% P ° 5 ^ '

(Magnel

2

M

( 9°

w i t n

S i

0 )> 2

A l u n d u m 1 1 3 9 , t h e c a 1 c i um f 1 t i o r i d e - a 1 umi n a c e m e n t ( C A F ) a n d last,

Coralbond. From t h e s e d a t a i t i s c l e a r t h a t t h e most a d v i s a b l e

r e f r a c t o r y f o r h o l d i n g I n c o n e l X-750 would a high percentage stability

of spinel

oxides, the ideal

T a y l o r 341 p e r f o r m e d h i g h e r than

and as l i t t l e as p o s s i b l e lowcombination

7 ppm i n i t i a l

being

w e l l w i t h an o x y g e n

that of the spinel

hand, Coralbond

Magnel/SP2.

c o n t e n t n o t much

based m a t e r i a l s .

r e a c h e d 6 0 ppm o x y g e n oxygen).

be one c o n t a i n i n g

On t h e o t h e r

i n 15 m i n u t e s

(from

S i n c e i t s main c h e m i c a l d i f f e r e n c e

from T a y l o r 341 i s i n t h e s i l i c a

content and the s l i g h t l y

h i g h e r P 0 g > i t c a n be c o n c l u d e d t h a t t h e p r e s e n c e

of these

2

o x i d e s makes C o r a l b o n d superalloys.

In a real

n e v e r be o b s e r v e d , surface/volume concerned due

t h e l e a s t s u i t a b l e cement f o r m e l t i n g f u r n a c e those h i g h oxygen

r a t i o ; however, as f a r as cement a t t a c k i s

t othe almost

constant

be t h e same o r e v e n low oxygen

pronounced,

p o t e n t i a l i n the metal,

in silica

i n t h i s i n s t a n c e , some e f f e c t on t h e s t a b i l i t y , presented a significantly comparable

more

high d r i vi ng- f o rce f o r the d i s s o l u t i o n . I t

can a l s o be n o t i c e d t h a t t h e v a r i a t i o n

for

will

o f c o u r s e , due t o t h e much more f a v o u r a b l e

the results will

and c o n s e q u e n t

values

silica

lower oxygen

contents.

superalloy melting, the i n i t i a l

activity has, since

value than

Peribond

Coralbond,

It i s unfortunate that in stage o fa heat

involves

46 carbon

d e o x i d a t i o n and hence

activity

o f l a r g e p e r i c l a s e g r a i n s b o n d e d by s m a l l e r g r a i n s , the working

areas exposed Fig.

to the

magnesia

h a v e b o t h MgO

and

in

MgO'Al 0 2

3

metal.

24 s h o w s a c r o s s s e c t i o n o f t h e i n t e r f a c e o f a

from the m e t a l .

The

observed

a n d t h e b r i c k i n F i g . 24 i s due a n d , on t h e r i g h t The

gap

h a n d s i d e , one

i n t e r f a c e when

between

to shrinkage can o b s e r v e

probably spinel. l a y e r would

1)

i n Mg

at

this

and Al , this

from the melt, d e s c r i b e d in a

by t h e f o l l o w i n g p r o c e s s e s :

Dissolution of s i l i c a

from the b i n d i n g phase

t h e p e r i c l a s e g r a i n , due

t o t h e v e r y low o x y g e n

the m e l t and

stability:

low s i l i c a Si0

metal

a periclase

The m e c h a n i s m f o r the f o r m a t i o n o f

be p r e c i p i t a t i o n

Al,Ni alloy

the

during cooling

p i e c e s of oxide a d h e r i n g to the metal

p o i n t i n t h e i n t e r f a c e a r e o f an o x i d e r i c h

2

of

p o t e n t i a l in

= S_i + 2 0

This process will cipitation

X-750

face of a c r u c i b l e d r i l l e d

a f t e r u s e , w h i l e F i g . 25 d e p i c t s t h i s

detached

1%

Magnel

S i n c e t h e M a g n e l b r i c k i s com-

a b r i c k with a diamond d r i l l w i l l

grain.

Peribond.

the meta 1 / r e f r a c t o r y i n t e r f a c e o f the

in this m a t e r i a l .

and s p i n e l

sample

silica

one c a n r a t i o n a l i z e t h e p r o c e s s e s o c c u r r i n g w h e n

is melted posed

to low

c o m p o u n d s s u c h as t h o s e p r o b a b l y p r e s e n t i n Observing

sample

s e v e r e a t t a c k even

c o n t r i b u t e w i t h oxygen

of the most s t a b l e o x i d e s .

f o r the

pre-

47 2) activity

D i s s o l u t i o n o f MgO

coefficient

reactive elements MgO 3)

due

in the melt

t o t h e v e r y low

a f t e r the

Formation

o f s p i n e l o v e r t h e MgO

(3a) 3A i n F i g . 26

o f s p i n e l i n e q u i l i b r i u m w i t h MgO,

reaction of

= Mg0-Al 0 2

s h o w n by l i n e 3B i n F i g . 2 6 . d e s c r i b e d by e q u a t i o n

(3b)

a thermodynamic viewpoint, any

by p r e c i p i t a t i o n

(3b)

3

I t i s c l e a r t h a t the

process

s h o u l d be t h e m o s t f a v o u r a b l e since line

3B w i l l

always

increases.

contents

t o be e x p e c t e d

T h i s i s due

o f t h e p r o c e s s , MgO

may

to the very

low

100

ppm

(3b) o v e r

be a d d e d i n a l a t t e r

step

b e c o m e t h e m o s t s t a b l e o x i d e , due

to

alloys.

(1) and t h e t h e r m o d y n a m i c a d v a n t a g e

( 3 a ) , f a v o u r r e a c t i o n (3b)

r e s p o n s i b l e f o r the formation One

process.

f a c t t h a t e n o u g h o x y g e n s h o u l d be a v a i l a b l e

l o c a l l y from process

probably

of

magnesium

t h e v e r y s t r o n g i n t e r a c t i o n o f Mg w i t h 0 i n N i c k e l

process

be

at t h i s stage of the m e l t i n g

in amounts over

The

from

o t h e r i n F i g . 26 as t h e o x y g e n c o n t e n t

the melt

Mg

on

A^O^,

2AJ_ + 30 + MgO

Should

grains either

3

a c c o r d i n g t o t h e e q u i l i b r i u m f i x e d by l i n e

before

melt:

melt, 2

reached

the

= Mg_ + 0

Mg_ + 2AJ_ + 40 = M g 0 - A l 0

and

addition of

a s s h o w n i n F i g . 26 f o r 1% A l i n t h e

d i r e c t l y p r e c i p i t a t e d from the

formation

oxygen

as t h e

of

one

of the s p i n e l l a y e r .

m u s t a l s o be a w a r e o f p o s s i b l e k i n e t i c d i f f e r e n c e s

between the p r e c i p i t a t i o n of alumina

or t h a t of s p i n e l , which

48 i n v o l v e more s p e c i e s and o f t h e i n t e r s o l u b i 1 i t i e s various oxides which

may

n o t be n e g l i g i b l e

of

at the

these

tempera-

tures in question. These essentially oxygen

r e a c t i o n s would all-spinel

lining

have the e f f e c t of p r o d u c i n g (or brick) with

e q u i l i b r i u m c o n c e n t r a t i o n which

f o r t h e h o l d i n g o f v e r y low oxygen a l s o a good for

evidence

of the s u i t a b i l i t y

around

3

the alumina

This is

behave almost

When one

produces

as p u r e

to understand

a complete

firing

sheath of

MgO-

s p i n e l , and hence w i t h X-750

A l u n d u m 1139

are e s s e n t i a l l y

and

Coralbond,

for their different

the

behaviour.

observ-

In

and b o t h

Mg

for spinel

precipitation.

One

oxide mixture.

In t h e c a s e i n q u e s t i o n , t h i s p r o v e d

mixture

the

role in

a b s e n t , t h e r e i s no chance

must then

best

alloy.

t h i s c a s e , s i n c e a l l cements are h i g h in a l u m i n a , a n d MgO

cement

achieve the

a t i o n o f t h e i n t e r f a c e a g a i n p l a y s an i m p o r t a n t e l u c i d a t i n g the causes

the

Since the

compares the l a r g e d i f f e r e n c e between

v a l u e s f o r T a y l o r 341,

look f o r the next most s t a b l e t o be

a

of chromium oxides with the oxides of the r e f r a c t o r y

a n d some t r a c e s o f o x i d e s o f o t h e r a l l o y i n g e l e m e n t s

2mm

linings

grains, i t is clear that this

v a l u e s f o r r e s i d u a l oxygen

Ti).

low

favourable

of a l l spinel

s h o w n by t h e c e m e n t S P 2 .

of the MgF^/A^Og mixture

will

be

activity metals.

on t h i s r a t i o n a l e i t i s e a s y

excellent stability

2

relatively

VIM. Based

A1 0

would

an

Alundum 1139, deep, behind

(such

as

f o r i n s t a n c e , p r e s e n t e d a pink l a y e r , about

the i n t e r f a c e , r i c h

in chromium.

This

agrees

w i t h t h e o b s e r v a t i o n s o f S p e n d e l o w ( 4 0 ) when m e l t i n g H a s t e l l o y

49 235

in

alumina

was

greenish,

shown i n

Fig.

crucibles. thin

and v e r y

27.

This

and chromium o x i d e the

case

dense,

of higher

the p a r e n t

crucible.

more open

structure

the

case

precludes

the is

case

a higher

and i m p e r v i o u s

(and

also

P).

minimum p e r c e n t a g e

alumina

(10 ) 5

cussed Al 0 2

3

as

it

the

to the melt 1139,

formation

'sees',

the

contains

The s u p e r a l l o y

alone

mixtures

to a c t as

is

dense

refractory,

essentially,

A1 0^, 2

i n t e r f a c i a l layer

a rather large in

and t h i s

question

contains

element i s (a . c

n

Q

a continuous

t o u n i t y , one s h o u l d source

In

formed of a

a mediocre /h

/ h ^ hg = 4.5 (10 ) ( 3) ) . 13

f t l

amount

9

.h si 0 As

the a c t i v i t y c o e f f i c i e n t of SiC^

close

than

however,

of a

i n t o the

in N i c k e l a l l o y s

compared t o a

before, since

Ti)

a real

o1 U£

6.18

in

some P and

as

o f Alundum

though

of s i l i c o n

d e o x i d a n t even when

as

oxygen e q u i l i b r i u m c o n c e n t r a t i o n .

o f C o r a l b o n d , even

dense

silica

seeks

the metal

can d i f f u s e

stages,

of

also

s t a b i l i t y with respect

the m e t a l , a t a l l

and hence

impervious,

r e a c t i o n , a l l o w i n g a lower

to surround

In

341

c o n c e n t r a t i o n than

(and c o n t a i n i n g

l a y e r and t h e chromium o x i d e while

higher

l i m i t s the e x t e n t of the

'crucible'

almost

l a y e r , composed m a i n l y

1139

oxygen p o t e n t i a l phase

its

l a y e r formed i n T a y l o r

i n somewhat

o f Alundum

probably

The

disin

expect t h i s

o f oxygen t o t h e m e t a l .

SiC^/ silica

50

CHAPTER 4 O B S E R V A T I O N S OF I N D U S T R I A L

SAMPLES

In o r d e r t o r e l a t e t h e e x p e r i m e n t a l a c t u a l VIM p r a c t i c e s and t o v e r i f y

r e s u l t s with the

t h e v a l i d i t y o f some o f

t h e o b s e r v a t i o n s made i n t h e t h e o r e t i c a l r e v i e w , from m a t e r i a l s used examined. de-S

i n o r produced

some

by VIM f u r n a c e s

were

These c o n s i s t o f a sample o f s l a g produced

treatment,

samples

of macro-inclusions

s u p e r a l l o y s ; and a Magnel b r i c k used

4.1

failed

i n VIM

in nickel

in a furnace

lining

prematurely.

S a m p l e o f S l a g U s e d i n VIM d e - S

Treatment

In o r d e r t o d e s u l p h u r i z e N i - b a s e

alloys, i t is a

k n o w n p r a c t i c e t o mak.e c a l c i u m o x i d e a d d i t i o n s t o t h e Although

i n most heats

t h e r e i s no problem,

violent slagging occurs analysed

base

melting

s t e e l s a n d n i c k e l - b a s e s u p e r a l l o y s , a n d a rammed VIM which

samples

i n some c a s e s

due t o r e f r a c t o r y a t t a c k .

i s from one o f t h o s e

charge. a

The sample

heats.

F i g s . 28 a n d 29 show t h e c h a r a c t e r i s t i c m i c r o s t r u c t u r e o f t h e s l a g , i n t h e SEM. of calcium aluminates,

The matrix

i s composed e s s e n t i a l l y

w i t h some o t h e r o x i d e s , a s s h o w n b y

t h e MgKa a n d A l K a p h o t o g r a p h s

i n F i g . 29, s e v e r a l small

o x i d e s u l p h i d e i n c l u s i o n s a n d l a r g e MgO

grains.

mixed-

51 The significant adequacy

f i r s t o b s e r v a t i o n t o be made i s r e l a t e d t o s u l p h u r c o n t e n t o f the s l a g , c o n f i r m i n g

of this treatment

the l a r g e magnesia

as a de-S

treatment.

However,

tory used, which

was

It i s c l e a r then

t h a t , a p a r t from d e s u l p h u r i z i n g the

magnesia

a d d i t i o n a l s o f l u x e s the b i n d i n g phase the c a l c i u m aluminates The

which

rammed

o f the l i n i n g

c a l c i u m o x i d e has been

the low m e l t i n g m i x t u r e s These,

combined

lime producing

o f MgO,

spinel

treatments,

absorbed and

to

calcium

produce aluminates.

w i t h the a b s o r p t i o n o f o x i d e s o f elements

as Z r and T i f r o m in t h i s

lining.

c a n be p o s s i b l y

a t t r i b u t e d to the c u m u l a t i v e e f f e c t o f v a r i o u s sufficient

refrac-

c o n s t i t u t e the bulk of the s l a g .

f a c t t h a t t h e f l u x i n g o c c u r s i n some h e a t s

until

the

g r a i n s c l e a r l y o r i g i n a t e from the a spine1-bonded

the

the s k u l l , have a very h i g h f l u x i n g

ability

system. It i s i n t e r e s t i n g to compare these o b s e r v a t i o n s

t h e c o m m e n t s by W a r d e t a l . ( 5 5 ) , w h e n e m p l o y i n g desu1phurization Magnesia

linings.

treatment

in e i t n e r Magnesia

He o b s e r v e d

a f t e r the t r e a t m e n t s Magnesia

such

definite

with

a lime

S p i n e l or

s w e l l i n g i n the

pure former

w h i l e no a l t e r a t i o n o c c u r r e d i n t h e

l i n i n g s , p r o b a b l y due

to the absence

of

alumina.

52 4 .2

Magnel

Brick

A sample of Magnel b r i c k from a l a r g e VIM

furnace

was

the working

lining

e x a m i n e d , both m a c r o - and

of

microscopic-

al l y . 4.2.1

Macroscopic

Metal was

f i n i n g was

the reason

still

Observation

why

the

found

i n the C o r a l b o n d

l i n i n g was

removed.

effort. i n VIM

This confirms

the o b s e r v a t i o n s

t h a t the w o r s t

b r i c k l i n i n g s i s at the working

of metal

also observed

( F i g . 30)

face

is

i n t o the Magnel b r i c k i t s e l f .

o f the r e g i o n c l o s e to the w o r k i n g 4.2.2

Microscopic

aluminates).

In o r d e r t o s t u d y observations

of calcium

metal

i n the r e f r a c t o r y ,

one

the mortar

can

and

aluminates

was

found

also expect

t o be

In a d d i t i o n , a s F i g s . 3 2

and

low

the

by w h a t a p p e a r s

bricks

The

pre-

rather intriguing, CaO

content

33 s h o w , t h e m e t a l

seems

i n t o the r e f r a c t o r y p a r t i c u l a r l y v i a these

This occurs

calcium

j o i n t s are

i n c l u s i o n content of the melt.

s i n c e Magnel i s s u p p o s e d to have a very

f i n d i t s way

w e r e made

i n c l u s i o n s ( s p i n e l , alumina

the weakest l i n k i n the system,

the

Observation

T h i s shows t h a t a l t h o u g h

to c o n t r i b u t e t o the

penetration

face.

F i g . 31 s h o w s some e n t r a p p e d which a c t u a l l y contains

problem

joints.

a considerable

mechanism of t h i s process, m i c r o s c o p i c

ates.

there

a c o n s i d e r a b l e w a s t e o f m a t e r i a l and b r i c k l a y i n g

One

6).

Since

which

quite a substantial thickness of brick a v a i l a b l e , this

represents

sence

joints,

t o be m e l t i n g

and

(Table to alumin-

dissolu-

53 tion

( F i g . 3 2 ) , o r p o s s i b l y by f l u x i n g w i t h

Ti0

or Zr0

2

2

(Fig. 33). The

calcium

aluminates

phase i n the p e r i c l a s e grains the

brick.

occur

a s an

intergranular

close to the working

When o n e o b s e r v e s t h e p e r i c l a s e g r a i n s

face o f i n unused

Magnel b r i c k , F i g . 34, one sees t h e t y p i c a l s t r u c t u r e p u r i t y p e r i c l a s e , i n w h i c h t h e MgO g r a i n s b o n d e d a n d b o n d e d by a c a l c i u m T h e r e has been c o n s i d e r a b l e tion o f this s i l i c a t e ratio

intergranular

phase.

phase, both with

respect

content

(77).

composi-

to the CaO/Si0 The C a 0 / S i 0

2

2

c o n t r o l , i n the system CaO/Si0 /Mg0, t h e amount and 2

temperature a t which

t h a t r a t i o_s g r e a t e r no

direct

w o r k d o n e on t h e d e s i r a b l e

(76) and to the impurity

ratio will the

silicate

are both

o f high

than

liquid will

be f o r m e d .

about 2 o r very

l i q u i d i s t o be p r e s e n t

at 1600°C.

I t i s known

low s h o u l d

be u s e d , i f

In t h e case

o f Magnel,

i t seems t h a t t h i s r a t i o i s a r o u n d ^ which i s recommended f o r E l e c t r i c furnace

and Open-Hearth a p p l i c a t i o n s

tent of impurities dihedral

angle

amongst those

(other

oxides)

h a s a m a r k e d e f f e c t on t h e

o f the l i q u i d phase, Alumina and T i 0 causing

pronounced lowering

promoting l i q u i d penetration refractory

( 7 7 ) . The con-

being

2

i n this angle,

hence

into the grain boundaries and

disruption.

When M a g n e l i s u s e d f o r s t e e l o r s u p e r a l l o y under vacuum, two main p r o c e s s e s tion of s i l i c a

and formation

T h e s e two p r o c e s s e s intergranular

occur.

Reduction

melting or dissolu-

of alumina a t the working

c a n l e a d t o an i n c r e a s e

l i q u i d phase o r t o the lowering

face.

i n the amount o f o f the liquid

54 formation

temperature.

g r a i n , 15 mm a w a y f r o m

Indeed,

F i g . 35, shows a p e r i c l a s e

the metal/refractory i n t e r f a c e where,

b e s i d e s t h e l a r g e r amount o f i n t e r g r a n u 1 a r compound, one n o t i c e s a change i n i t scomposition and

an i n c r e a s e i n a l u m i n a

content.

with

a decrease

As o n e g e t s

the i n t e r f a c e , t h e r e i s v i r t u a l l y no s i l i c a granular liquids probably

are b a s i c a l l y o f the system

with small

left

in silica

closer to and the i n t e r -

CaO/A1^O^/MgO ,

fluxing additions of other oxides, f o r

instance TiO^. One

can a l s o observe,

the presence

i n some i n s t a n c e s

of a layer of calcium aluminates

the m e t a l ,

probably

of

course,

be a p o s s i b l e s o u r c e

in

the melt. Although

(at

drained intergranu1 ar liquid. This of calcium aluminate

importance chemical 2

than

small

shows t h a t

even

they would

have

I t a l s o draws a t t e n t i o n t o t h e

o f the t o t a 1 a n a l y s i s o f the r e f r a c t o r y , both a n d p h y s i c a l , s i n c e t h e c o n c e n t r a t i o n o f CaO a n d

i n an i n t e r g r a n u l a r p h a s e makes t h e b r i c k l e s s r e s i s t a n t i t c o u l d b e i f , s a y , f u s e d MgO g r a i n s , o f t h e s a m e

composition

were

Fig. at

will,

ther e f r a c t o r i e s

contribute i n c l u s i o n s , although

a much l o n g e r u s e f u l l i f e .

with

inclusions

t h e a t t a c k on t h e b r i c k i s o b v i o u s l y

i f a more s u p e r i o r cement were d e v e l o p e d ,

Si0

in contact

l e a s t c o m p a r e d t o t h a t on t h e j o i n t s ) t h i s

would s t i l l

(Fig. 36),

the working

bulk

used.

37 s h o w s a l a y e r o f s p i n e l o v e r a p e r i c l a s e g r a i n face, supporting the experimental

observations

p r e s e n t e d e a r l i e r a n d t h e t h e o r y t h a t s p i n e l s h o u l d be t h e

55

most s t a b l e oxide phase i n c o n t a c t with N i c k e l - b a s e d

super-

a l l o y c o n t a i n i n g high percentages o f aluminum i n a Magnel cruci ble.

56 4.3

Inc1usions

in Ni-Based

Although produces

Superalloy

i t i s w e l l known t h a t v a c u u m i n d u c t i o n m e l t i n g

c l e a n e r m a t e r i a l than a i r m e l t i n g

a r l y i n the case this is mainly the system, nitrides.

(5, 51),

particul-

of superalloys containing r e a c t i v e

elements,

due

to the e l i m i n a t i o n o f the atmosphere

p r e v e n t i n g the e x c e s s i v e One

by m e c h a n i s m s s u c h

r e f r a c t o r i e s can

as e r o s i o n , a n d

discussed in the previous

that stable nitrides

chemical

I t i s now

I t becomes then

tion

attack

as

in the

promote the formation alloy with

to recognize that there w i l l

products

o r VAR

of paramount importance

as f e r r o - c h r o m i u m

are

and

alloy.

to control

of those

inclu-

high nitrogen

content,

B e s i d e s , one

must

be s o m e i n c l u s i o n f o r m a -

from the r e f r a c t o r i e s , s i n c e a l l o b s e r v a t i o n s

no p r e s e n t VIM

produced

as T i ( C N ) )

i n VIM

f e r r o a l l o y s with high oxide content, etc. be r e a d y

be

well established

h e n c e , once f o r m e d , wi11 most 1 i k e l y remain

the f a c t o r s t h a t w i l l

still

and c a r b o n i t r i d e s ( s u c h

h a r d l y a f f e c t e d by t h e u s u a l t r e a t m e n t

and

that

c h a p t e r , and t h a t t h e s e

i n m o s t c a s e s , be o x i d e s .

s i o n s , such

of oxides

m u s t be a w a r e , h o w e v e r , o f t h e f a c t

'exogenous' i n c l u s i o n s from

will,

formation

from

r e f r a c t o r y c a n be c o n s i d e r e d t o t a l l y

show t h a t inert

under the p r o c e s s i n g c o n d i t i o n . In o r d e r t o i l l u s t r a t e of Ni-based

these

s u p e r a l l o y f r o m a VIM

c o m m e n t s , some

f u r n a c e were

samples

examined.

F i g . 38 s h o w s ca 1 c i um a 1 umi n a t e i n c l u s i o n s t r i n g e r s in a p a r t i a l l y these

f o r g e d VIM-VAR s u p e r a l l o y .

i n c l u s i o n s i n more d e t a i l

When o n e

t h e y show s m a l l

examines

entrapped

57

m e t a l p a r t i c l e s a n d a r e s u r r o u n d e d by s m a l l e r nitrides

( F i g . 39).

This would i n d i c a t e that they

p a r t i a l l y m o l t e n a t some s t a g e they

tend

to c l u s t e r during

due t o f a v o u r a b l e

titanium

surface

of the processing

melting

were and

and r e m e l t i n g ,

that probably

energy considerations.

I n F i g . 40

one s e e s a s p i n e l i n c l u s i o n , f o u n d i n a n o t h e r s a m p l e the

same m a t e r i a l .

core

or these should

composition addition

(since there

i n t h i s case

form o f a small ments).

products

i n c l u s i o n s , i t seems r a t h e r

i f not f o r t h e i r size nucleated

i n the m e l t ) ,

i s no i n t e n t i o n a l c a l c i u m

addition

i n t e r a c t i o n s observed

previously

These i n c l u s i o n s would only

and l a t e r i n t o the

were since

the formawithout

into the

ingot.

One i s l e f t t h e n

r e m o v i n g them, by a d e q u a t e p o u r i n g and h o l d i n g

improve-

have t o c l u s t e r i n

and p r a c t i c e , t h e f o r m a t i o n

c a n n o t e a s i l y be a v o i d e d .

a slag.

o r CaO

inclusions

It i s a l s o c l e a r that i n the present

dish design

for their

the b r i c k s ,

the m e l t w h e t h e r f l o a t i n g o r n o t a n d f i n d t h e i r way

tory technology

(too large

inclusions

could explain

tion of large s p i n e l or calciurn aluminate

tundish

materials

o f Ni-Mg a l l o y f o r w o r k a b i l i t y

I t i s e a s i e r to believe that those

difficulty.

clear

and the only magnesium added i s i n the

formed from i n t e r a c t i o n s o f the metal with the

discuss

be r e l a t e d t o r e f r a c t o r y

e m p l o y e d i n t h e VIM f u r n a c e , t o be d e o x i d a t i o n

from

Although i t i s not our purpose to

in depth the genesis that t h e i r oxide

carbo-

time,

state of refraco f these with

temperature

inclusions

the option control,

and perhaps a l s o p o u r i n g

of

tunthrough

58

4.4

P i e c e o f Rammed L i n i n g As d i s c u s s e d b e f o r e , i n d u s t r i a l l y , t h e a l t e r n a t i v e t o

brick/cement

lining

i s a rammed l i n i n g .

c a r e f u l l y sized mixture roughly

in a 60%MgO/40%A1 0 2

superalloy Nimonic 4.4.1

failed

t i o n on t h e w o r k i n g

3

case,

p e r i c l a s e and

composition

was

a

silica,

used to melt

the

901.

Macroscopic

The

these

of alumina,

In t h i s

Observation

l i n i n g shows metal f a c e arid m e t a l

c r a c k s b e i n g the

reason

why

i n c r u s t a t i o n and

fins the

along cracks

l i n i n g was

penetra(Fig.

removed

41)

from

service. 4.4.2

Microscopic

Observation

F i g . 42 s h o w s t h e s t r u c t u r e o f t h e away f r o m t h e m e t a 1 / r e f r a c t o r y

interface.

rammed l i n i n g

I t shows a s i n t e r e d

m a t r i x e s s e n t i a l l y composed of s p i n e l , s u r r o u n d i n g periclase

grains.

t h e l a r g e MgO presented

The

very

much

forwarded

for

most i n t e r e s t i n g c h a r a c t e r i s t i c o f the

mat-

i s t h a t t h e s i n t e r i n g i s q u i t e i n h o m o g e n e o u s , i . e . , some

regions are densely probably CaO

large

in the s l a g sample p r e v i o u s l y

(4.1), in agreement with the theory

their origin. rix

These p e r i c l a s e g r a i n s , resemble

g r a i n s found

6cm

bonded, while others are porous

l o o s e l y bonded.

ratio The

One

also observes

i n d i c a t i n g the p o s s i b l e presence

and

a very high of

oxides.

2

forsterite.

m e t a l / r e f r a c t o r y i n t e r f a c e s h o w n i n F i g . 43

sents a l a y e r of T i / A l

Si0 /

T h i s l a y e r , as i n t h e

pre-

case

Magnel b r i c k s , c o n t r i b u t e s macro i n c l u s i o n s to the melt

of

when

59 eroded

( F i g . 4 4 ) . C1 o s e t o t h i s 1 a y e r , t h e r e i s c o m p l e t e

dep1etion

o f s i l i c a i n the r e f r a c t o r y , the i n t e r g r a n u l a r volumes b e i n g filled

by m e t a l

layerandby

i n a region very c l o s e to the T i / A l

oxide

T i / C e o x i d e mi x t u r e s f u r t h e r i n t o t h e 1 i n i n g ( F i g . 4 5 ) .

T h i s c a n be r a t i o n a l i z e d i n t h e f o l l o w i n g m a n n e r . Silica

d i s s o l v e s i n t h e low o x y g e n a c t i v i t y

the oxygen content tion.

locally

i n t o the range

In t h e c a s e o f N i m o n i c

(as c o m p a r e d to X-750) and

901,

both

alloy,

of oxide p r e c i p i t a -

the high T i

t h e h i g h Fe c o n t e n t

oxides

cases.

to the m e l t ,

t h e Mg

and

decreases

of

Ti/Al

as o b s e r v e d

Since there is very l i t t l e

MgO

exposed

Titanium oxides

are e x c e l l e n t fluxes in

s h o u l d d i f f u s e r e a d i l y i n t o the l i q u i d

matrix,

d e c r e a s i n g the d i h e d r a l a n g l e , i n c r e a s i n g the amount of p h a s e and

hence enhancing

grains of r e f r a c t o r y . p o s s i b l e that a heat

The

metal

l i t t l e evidence

liquid

by s e p a r a t i n g

the

i t i s not known, i t i s q u i t e

from t h i s l i n i n g would c o n t a i n a s l a g caused

by CaO

a d d i t i o n as

s u b s t i t u t e d by t i t a n i u m

discussed

oxide.

f i n / r e f r a c t o r y c r a c k i n t e r f a c e shows of reaction.

s h o u l d h a v e o c c u r r e d due geneous expansion

the a t t a c k p r o c e s s

Although

v e r y s i m i l a r t o t h e one b e f o r e , w i t h t h e CaO

in

a v a i l a b l e for s p i n e l p r e c i p i t a t i o n would

be r e a d i l y e x h a u s t e d . t h i s system

and

the p r e c i p i t a t i o n of a mixture

i n s t e a d o f C r / A l o r Mg/Al o x i d e m i x t u r e s

the p r e v i o u s

content

(which

i n c r e a s e s t h e e f f e c t i v e n e s s o f T i as a d e o x i d a n t t h a t of Cr) f a v o u r s

bringing

This i n d i c a t e s t h a t the

to thermal

s t r e s s e s caused

o f t h e l i n i n g , and

wets the r e f r a c t o r y and

penetrates

t h a t the metal

i n t o the

crack.

very crack

by

inhomo-

simply

60 One a l s o n o t i c e s n o a l t e r a t i o n i n t h e f u s e d MgO ( F i g . 46) w h i c h a r e e v i d e n t l y more s t a b l e than

grains

the s i n t e r e d

p e r i c l a s e grains of Magnel. The ment w i t h

presence

of cerium

i s probably

REM, a s d e s c r i b e d b y C r e m i s i o

is a very e f f e c t i v e technique

due t o a de-S t r e a t -

(63) and o t h e r s .

and i t s use has been

This

discussed

p r e v i o u s l y , the only p r a c t i c a l l i m i t a t i o n to i t s a p p l i c a t i o n being

t h e REM r e s i d u a l s a n d c a r r y - o v e r Rothman

into the f i r s t performed. Cremisio

problems.

( 6 5 ) r e p o r t e d a s i g n i f i c a n t c a r r y - o v e r o f Ce heat

Although

i n a c r u c i b l e a f t e r t h e REM t r e a t m e n t

he a t t r i b u t e d t h i s o n l y t o t h e s k u l l ,

(63) suggested

t h a t the r e f r a c t o r i e s c o u l d play a

r o l e i n t h e r e v e r s i o n o f Ce i n t o t h e s u b s e q u e n t its recovery

was

uncertain.

I t i s also noteworthy

heats, that

making

Cremisio

w h e n Ce d e s u l p h u r i z i n g N i m o n i c 9 0 1 r e p o r t e d t h e " d e v e l o p m e n t o f an i n n o c u o u s

' o x i d e - l i k e ' c o v e r on h e a t s

containing

which would c e r t a i n l y confirm our observations

on t h e

o f Ce i n t h e l i q u i d p h a s e o f t h e r e f r a c t o r y , e n h a n c i n g mechanical

break-up.

cerium" presence its

61

CHAPTER 5 CONCLUSIONS AND 5a. simulate

The

the

materials

tests

initial

(less

deoxidized.

In

be e s s e n t i a l l y

with

the

obvious

of

superalloys

the h e a t ,

in which

r e a c t i v e elements)

this

will

performed with

part

the

RECOMMENDATIONS

stage, the

however,

same as

differences

are

the a t t a c k

that

of the

t h a t the

in a s u p e r a l l o y

is

in

AISI

steel,

the p r o c e s s i n g

substantially

lower

Hence, observed melting

the

fact that melting

t o be more

aggressive

of N i c k e l - b a s e d operating

a t the

steel/refractory 5b.

presence

The e x t r e m e l y

in metals

low o x y g e n - l o w

silicon

as

in

a component

Unfortunately,

for

used f o r refractory

totally silica

refractory its

refractory

frustrates

f o r VIM as

make

it

of a r e f r a c t o r y .

used present

is

of

are

steels.

usually than to

the

attack

products

time. of

silica

or it

in

in

the

contact

a very

poor

with choice

applications.

excellent

difficult

most a t t e m p t s

that

an i m p u r i t y

fabrication, its

production design

makes

presence

carbon

related

absence

vacuum

superalloys

besides

f r o m the also

any

under

tests,

refractories

low s t a b i l i t y

carbon

mechanism

f o r most

steel

a t any

raw

temperatures

can be

and the

interface

than

than

of

to the

superalloys

temperature

of carbon

lower

for Ni-supera11oys

higher

ores

that

much

of

not

and

steel

amount

deoxidant

and

the

molten

as

1095

do

i n many properties

to e x c l u d e

The

it

low s t a b i l i t y

t o combine

it

in

of

a lower

62

a c t i v i t y f o r m - - s u c h as m u l 1 i t e - - t o elements. selects with be

From t h e s e

conclusions

a cement ( o r any

to i t s s i l i c a

furnace,

content,

by

reacti

i t i s c l e a r t h a t when

refractory that will

t h e m e t a l ) f o r a VIM

given

reduce i t s attack

be

in

contact

special attention

i f the

best

one

should

r e s u l t s are

to

be

achieved. A l t h o u g h the silica

containing

to the

reaction

observation

c o n t r o l l i n g step

c e m e n t s s e e m s t o be

of the

hope t h a t s t e e l

altered portion in t h i s context)

' w a s h - h e a t s ' may

that there

of the b i n d i n g

the

properly

as a l i n i n g

silica

is hardly

to the m e t a l , during

the

the

layer.

The

fragile

and

that would

charging

any

any

l i n i n g by

phase r e s u l t s in a very adhering

physical

a c t u a l l y accomplish

o f a s i 1 i c a - d e p l e t e d , more s t a b l e

porous l a y e r , strongly function

(difusion)

of the medium-high

w a s h i n g , in the sense of c o n d i t i o n i n g

removal

its transport

of

i n t e r f a c e , i t i s a l s o c l e a r , from the

c e m e n t s ( 5 - 1 0 % S i 0^

production

in the c o r r o s i o n

not

o f the

next

heat. One

mi g h t

t o be u s e d , t h e y preferably with

the

should

be o f v e r y

of a Nickel-base

The

cement grains

and

i n any

stability.

use

Best

that i f firing low

heats

t h i s be

compatible

firing.

o f f l u o r i d e s to promote the

t h e i r reaction with

the

bonding

refractory

of the t e s t s , compromise the b a s i c r e s u l t s are

of elements which form oxides o f the m o r t a r o r the b r i c k .

are

r e a c t i v i t y , and

a l l o y , should

temperatures needed for 5c.

did not,

r e commen d t h e n ,

obtained

by s e l e c t i n g

that react with In some c a s e s

the

of

bricks grain

fluorides basic

as s h o w n i n

oxide the

63 tests of CaF2/Al20

3

of the b a s i c alumina and

improved

alloy.

and

M g F g / A ^ O ^ c e m e n t s , t h e same

was

observed

s t a b i l i t y was

The

stability

when i n c o n t a c t w i t h

steel

shown when i n c o n t a c t w i t h a

f a c t t h a t the f l u o r i d e - c o n t a i n i n g mixtures

w i t h Magnel b r i c k s enhances t h e i r cementing

superreact

properties.

It is

f e l t t h a t t h e u s e o f t h e A l 2 0 / M g F 2 / M g O c o m p o s i t i on

developed

i n t h i s work w i t h a more r e a c t i v e and b e t t e r s i z e d

alumina

3

powder and c o n t r o l l e d a d d i t i o n s o f l i g n i n

s u l p h i t e to

the b r i c k l a y i n g needs would present a d e f i n i t e the chemical analogous

s t a b i l i t y o f t h e VIM

composition,

present very promising

results.

i m p r o v e m e n t can p r o b a b l y ( A l F ^ o r MgF2) f o r s i l i c a MgO/40%Al20

3

5d.

improvement in

furnace linings.

u s i n g a b a s i c MgO

satisfy

g r a i n and

Also,

an

A l s h o u l d

As a c o r o l l a r y , c o n s i d e r a b l e

be a c h i e v e d by s u b s t i t u t i n g f l u o r i d e s i n ramming m i x t u r e s

such

as t h e

60%

previously described. The

p h y s i c a l c h a r a c t e r i s t i c s o f t h e r e f r a c t o r y can

h a v e a d e f i n i t e i n f l u e n c e on t h e k i n e t i c s o f a t t a c k , as s h o w n by t h e t e s t s w i t h f i r e d a n d u n f i r e d T a y l o r 320 c e m e n t . in a l l cases, f i r i n g to a temperature

This suggests that

as h i g h a s p o s s i b l e s h o u l d be

a t t e m p t e d , b e f o r e b r i n g i n g a new l i n i n g o r t u n d i s h i n s e r v i c e . T h i s w i l l a l s o h a v e f a v o u r a b l e e f f e c t s on t h o r o u g h l y d r y i n g t h e refractories.

One

should not expect,

however, dramatic

ments i n the c a s e o f m a t e r i a l s o f r e c o g n i z e d low 5e.

Since the presence

of comparatively

ages of aluminum (or other elements

with

stability. high

high a f f i n i t y

oxygen) s u b s t a n t i a l l y lowers

the a c t i v i t y c o e f f i c i e n t

oxygen in a s u p e r a l l o y melt,

the oxygen c o n t e n t

will

be g o v e r n e d

by t h e f o l l o w i n g f a c t o r s :

improve-

percentfor of

in these a l l o y s

64 1.

Phases (and compounds) p r e s e n t a t the metal/ refractory interface

2.

Time o f h o l d i n g i n the c r u c i b l e

3.

Physical c h a r a c t e r i s t i c s of the i n t e r f a c e .

The

first

factor will

c o n t r o l the e q u i l i b r i u m oxygen

c o n t e n t o f t h e a l l o y , by f i x i n g t h e o x i d e a c t i v i t i e s , the o t h e r two w i l l dissolution

determine

while

the kinetics o f the oxide

process.

It follows then, that the best s e l e c t i o n o f a r e f r a c t o r y f o r VIM ( f o r b o t h mixture

s t e e l s and s u p e r a l l o y s ) w i l l

be a

o f o x i d e s w i t h as h i g h as p o s s i b l e a s t a b i l i t y

r e s p e c t t o c a r b o n , high m e l t i n g p o i n t and good properties.

mechanical

A l s o , aluminum i s u s u a l l y present i n high

q u a n t i t i e s i n s u p e r a l l o y s t o be t h e e l e m e n t t h a t w i l l the oxygen p o t e n t i a l . low a l u m i n a

with

activity

enough control

I t i s t h e r e f o r e d e s i r a b l e t o have as as p o s s i b l e i n t h e r e f r a c t o r y i n o r d e r t o

drive the equi1ibriurn 2A1_ + 30 = A 1 0 2

3

(in the r e f r a c t o r y )

as m u c h a s p o s s i b l e t o t h e r i g h t . conforms almost

M a g n e s i urn -a Tumi n a t e

p e r f e c t l y to this description--apart, of

c o u r s e , from t h e mechanical

c h a r a c t e r i s t i c s p o i n t o f view,

w h i c h i s v e r y much a f u n c t i o n o f m a n u f a c t u r i n g Indeed,

technique.

t h e b e s t r e s u l t s w i t h s u p e r a l l o y s were o b t a i n e d

r e f r a c t o r i e s with high percentages The apparent

spinel

importance

by c o m p a r i s o n

w i t h T a y l o r 341

and,

of mechanical

with

of spinel. characteristics

o f the r e s i d u a l oxygen values

i s made obtained

Alundum 1139 i n t h e s u p e r a l l o y t e s t s .

65 Although

the former

c o n t a i n s some m o r e l o w e r s t a b i l i t y

the f a c t t h a t a dense complex allows the achievement Coralbond, stability

x

z

layer is

o x i d e s , e s p e c i a 1ly s i 1 i c a , hinders the

will,

any

possibility

c a s e , p r o m o t e e r o s i o n and

the b r i c k s p r e s e n t l y used

i n VIM,

i n t o the

In

when

kept

introduce

melt.

In o r d e r t o a c h i e v e will

de-S,

i t seems t h a t e i t h e r

be i n t r o d u c e d a n d

Earth treatments--or

with

lime mixtures

will

h a v e t o be u s e d .

such

accepted

by t h e

that less orthodox

users--

Volkov

I t i s e v i d e n t t h a t t h e use under

new

treatments,

as t h e one. d e s c r i b e d b y

r e f r a c t o r i e s w o u l d be i d e a l

of

(61)

lime

vacuum m e l t i n g c o n d i t i o n s ,

s i n c e t h e i r main m e t a l l u r g i c a l 1 i m i t a t i o n - - i n a b i 1 i t y to FeO

fluxing--is

problems time w i l l

removed under

before they w i l l

f u r n a c e on a r e g u l a r b a s i s . note tages

However, the and

be u s e d

in the p r o d u c t i o n

hydration

i n any

industrial

a s n o t i c e d by S c h l e g e l

VIM

I t i s e s p e c i a l l y i n t e r e s t i n g to p r e s e n t many

o f l i m e r e f r a c t o r i e s , a c t i n g as

b i n d i n g agent

resist

i t s e e m s t h a t some

t h a t t h e u s e o f c a l c i u m f l u o r i d e may

s i n t e r i n g and ance,

vacuum.

h a v e y e t t o be c i r c u m v e n t e d pass

in

degenera-

i n c l u s i o n s i n the melt.

in c o n t a c t with the a l l o y s in q u e s t i o n w i l l

techniques

lower

content.

lining, producing

a d d i t i o n , even

inclusions

of

of

use o f s i ags o r l i m e a d d i t i o n s t o the m e l t

in almost

t i o n o f the

formed,

In t h e c a s e

however, the c o n s i d e r a b l y higher content

5 f . :Jhe

as Rare

W

of very good r e s u l t s .

o f a c h i e v i n g a low o x y g e n

VIM

(Al CryTi )0

oxides,

and

improving

(78).

the h y d r a t i o n

advana resist-

66

Even

though

the chemical upgrading of the p r e s e n t l y

used r e f r a c t o r y b r i c k s would

be p o s s i b l e - - b y t h e u s e o f

(CaO + S i 0 ) p e r i c 1 a s e o r f u s e d MgO 2

grains i n s t e a d of the

p r e s e n t l y used p e r i c l a s e , f o r i n s t a n c e - - o n e would likely

t o f i n d e r o d e d g r a i n s and i n c l u s i o n s

still

in the

i.e.,

emphasis

s h o u l d be p l a c e d on p o u r i n g

of

concerned,

facilities,

the c o r r e c t s e l e c t i o n of p o u r i n g t e m p e r a t u r e s ,

d e s i g n and c o n s t r u c t i o n , time i n the l a d l e .

be

metal.

I t seems t h e n t h a t , as f a r as i n c l u s i o n s a r e the main

lower

The

tundish

possibility

p o u r i n g t h r o u g h a l o w - m e l t i n g f u s e d s l a g s h o u l d a l s o be

studied.

67

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Vac.

M e t a l 1., No.3 , ( 1 9 6 3 ) ,

P o l y a k o v , A.Yu., e t a l . , Akad.Nauk. SSSR, I z v . Met.i G o r n o e D e l o , No.3 , ( 1 9 6 4 ) , 37 L i n c h e v s k i y , B.V.,

i b i d . , No.

2,

(1963),

25

V o l k o v , S.Ye., e t a l . , Rus.

M e t a l l . , No.4,

S c h l a t t e r , R.,

Pat. 3,853,540; Dec.10,

e t a l . , U.S.

(1964),

24 1974.

C r e m i s i o , R.S., C a n n o n , J.G. and E l l i o t , C . F . , i n " P r o c . o f t h e T h i r d I n t . S y m p . on E l e c t r o s l a g a n d O t h e r Special M e l t i n g T e c h n o l o g i e s " , Part I I I , Bhat, G.K. a n d S i m k o v i c h , A. ( e d s . ) , A S M - A V S , P i t t s b u r g h , (1971), 1 B a i l e y , R . E . , S h i r i n g , R.R. a n d A n d e r s o n , R . J . , i n " S u p e r a l l o y s : M e t a l l u r g y and M a n u f a c t u r e , P r o c . o f t h e T h i r d I n t . S y m p . , 1 9 7 6 " , K e a r , B.H., e t a l . ( e d s . ) , C l a i t o r P u b l . C o . , B a t o n R o u g e , ( 1 9 7 6 ) , 109 R o t h m a n , M.F., i n " V a c u u m M e t a l l u r g y " , ( P r o c . V a c . M e t . C o n f . 1 9 7 7 ) , K r u t e n a t , R.C. ( e d . ) , S c i e n c e P r e s s , P r i n c e t o n , ( 1 9 7 7 ) , 49 A s h l e y , W.E.,

private

communication

A r m s t r o n g , W.M., C h a c k l a d e r , A . C D . and Met. S o c . A l M E , 227, ( 1 9 6 3 ) , 1109

Rose, D.J.,

Trans.

R o s e n q v i s t , T., " P r i n c i p l e s o f E x t r a c t i v e M e t a l l u r g y " , M c G r a w - H i l l , New Y o r k , ( 1 9 7 4 ) B u t t , Y u . M . , T i m a s h e v , V.V. a n d S u ' i i m e n k o , L.M., I z v . A k a d . N a u k . S S S R . , N e o r g . M a t . , 5_, No. 6 , ( 1 9 6 9 ) , 1116

72 Pirogov, A.A., et a l . R e f r a c t o r i e s ( 1 9 7 0 ) , 39

(Ogneupory)

O ' H a r a , M . H . , Duga, J . J . and S h e e t s , B u l l . , 5_i, No. 7 , ( 1972) , 590

J r . , H.D.,

No.l, Cer.

K h o r o s h a v i n , L . B . , D o l g i k h , G.V. and V.M. U s t y a n t s e v , R e f r a c t o r i e s ( O g n e u p o r y ) , N o . 8 , ( 1 9 7 0 ) , 509 M a s s , V . H . and A b r a t i s , H . , A r c h i v wesen , 4JD, ( 1969 ) , 153 Sveshkov, Y u . V . , K a l m i k o v , V.A. Me t a l l . , N o . 4 , ( 1972) , 29 K u l i k o v , I.S., "Deoxidation Moscow, (1975)

f u r das

and A g e y e v ,

of M e t a l s " ,

EisenhuttenP.Ya.,

Rus.

Metallurgya,

K a p p m e y e r , K.K. and H u b b l e , D.H., i n " H i g h T e m p e r a t u r e O x i d e s " , p a r t I, A l p e r , A . M . , (e d. ) , vAcademi c P r e s s , New Y o r k , ( 1 9 7 0 ) , 2. White,

J . , ibid,

Schlegel,

E.,

77

East

Ger.

Patent 59,500,

Jun 2 5 ,

1966

73

FIGURES

74

h/Miins.

boiling

surface tion

d e s o r p

free oxygen uptake

t(min)

Fig.

1 Theoretical

deoxidation

diagram

(8)

75

Fig. 2

Deoxidation

Curves

(II)

76

—

—

019

i

t 15

i

30 i

1 -*

Fig. 3

i

I4.5

Dimensions of the c r u c i b l e s

used in the t e s t s

(mm).

Different wetting

behaviours

78

Spot infrared pyrometer Pyrex glass Rubber cork Dismantable Pyrex extension

-Brass joint

Quartz tube High alumina cement ( applied over Zr 0 ) 2

Zirconia felt Molten metal Crucible Water cooled HF coil Alumina rod Brassjoint

Vacuum gauge Baffle to diffusion pump rotary pump 8

DETAIL

Fig. 5

Experimental

'A'

Apparatus

valve

6

V a r i a t i o n i n c a r b o n c o n t e n t o f A-ISI 1095 melted in Tasil-X crucibles

steel

80

C

Fig.

7

I n t e r f a c e AISI 1095/Tasi1-X. a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) S i l i c o n X - R a y map

X2400

81

Fig. 8

M i c r o s t r u c t u r e o f T a y l o r 320. Secondary Electrons a) D r i e d a t 6 0 0 ° C b) F i r e d a t 1 0 0 0 ° C

X120,

82

phi

Fig. 9

I n t e r f a c e AISI 1095/Alundum 1162. x48 a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) S i l i c o n X - R a y map

Melt time 5 min.

83

Fig.

10

T y p i c a l m i c r o s t r u c t u r e o f a c e m e n t made Al 0 and CaF (CAF). X300. 2

a) b) c) d)

3

2

Backscattered Electrons O x y g e n X - R a y map A l u m i n u m X - R a y map C a l c i u m X - R a y map

from

d

c Fig.

11

Adherence t e s t .

I n t e r f a c e Magnel/CAF.

a) S e c o n d a r y E l e c t r o n s b) Magnesium X-Ray map c ) Aluminum X-Ray map d) C a l c i u m X-Ray map

X240

F i g . 12

V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n CAF c r u c i b l e s

1095

steel

Fig.

13

V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n A l u n d u m 1139 c r u c i b l e s

1095

steel

c Fig.14

T y p i c a l m i c r o s t r u c t u r e o f a c e m e n t made A l 0 and MgF ( S P 2 ) . X240 2

3

2

a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) M a g n e s i u m X - R a y map

from

Fig.

15

V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n SP2 c r u c i b l e s

1095

steel

89

C

Fig.

16

Adherence test. Interface Magnel/SP2 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map

X240

Fig.

17

V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n T a y l o r 341 c r u c i b l e s

1095

steel

Fig.

18

I n t e r f a c e AISI 1 0 9 5 / T a y l o r 341. X 40, S e c o n d a r y E l e c t r o n s

M e l t t i m e 15

min.

F i g . 19

V a r i a t i o n i n c a r b o n c o n t e n t o f A I S I 1095 s t e e l m e l t e d i n C o r a l b o n d o r T a s i l - X c r u c i b l e , as a f u n c t i o n o f th

c F i g . 20

I n t e r f a c e AISI 1095/Coralbond. X24 a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) S i l i c o n X - R a y map d) P h o s p h o r o u s X - R a y map

d

M e l t t i m e 15 m i n .

F i g . 21

Detail of altered Coralbond (Fig.20). a) S e c o n d a r y E l e c t r o n s b ) S i l i c o n X - R a y map c ) P h o s p h o r o u s X - R a y map

X60

95

F i g . 22

Alumina i n c l u s i o n s from Coralbond. Interface AISI 1095/Coral bond. X1000, Secondary E l e c t r o n s

F i g . 23

Equilibrium

A1 (K=2AJ_+ ?

30,

in Nickel

F i g . 24

I n t e r f a c e X-750/Magne1. X240 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map

M e l t t i m e 15 m i n .

b

c Fig.

25

Interface

X-750/Magne1, metal

a) S e c o n d a r y E l e c t r o n s b) Magnesium X-Ray map c) A l u m i n u m X-Ray map

removed.

X17

99

F i g . 26

Deoxidation

equilibria

i n a N i - 1 % A1

Alloy

100

F i g . 27

Dense l a y e r formed a t i n t e r f a c e X-750/Taylor X1000, B a c k s c a t t e r e d E l e c t r o n s

341

101

F i g . 28

M i c r o s t r u c t u r e of s l a g from d e s u l p h u r i z a t i o n treatment. X60, S e c o n d a r y E l e c t r o n s

102

C

F i g . 29

M i c r o s t r u c t u r e o f slag from d e s u l p h u r i z a t i o n X120 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i nurn X - R a y map

treatment.

e

F i g . 31

Cross s e c t i o n o f working face o f Magnel b r i c k ( F i g . 3 0 ) . X60 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map d) C a l c i u m X - R a y map e ) N i c k e l X - R a y map

b

c Fig.

32

Metal p e n e t r a t i o n i n Magnel b r i c k v i a CalciumAluminates. X480 a) S e c o n d a r y E l e c t r o n s b) N i c k e l X - R a y map c ) C a l c i u m X - R a y map

106

F i g . 33

Metal p e n e t r a t i o n i n Magnel b r i c k - - C a 1 c i u m - A l u m i n a t e c o n t a i n i n g T i t a n i u m and Z i r c o n i u m . X600 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map

107

F i g . 34

Detail brick.

of a P e r i c l a s e grain i n Unused X1000, S e c o n d a r y E l e c t r o n s

Magnel

b

F i g . 35

P e r i c l a s e g r a i n i n U s e d M a g n e l b r i c k , 15mm working face. Secondary electrons. a) X60 b) X 6 0 0

from

109

b F i g . 36

C a l c i u m - a l u m i n a t e s on t h e w o r k i n g X480 a) S e c o n d a r y E l e c t r o n s b) C a l c i um X - R a y map

face of

Magnel

Fig.

37

S p i n e l l a y e r on t h e w o r k i n g f a c e a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map

of Magnel

X60

Fig.

38

Macroinc1 usions i n p a r t i a l l y Superalloy. X200, Secondary

forged N i c k e l - b a s e d Electrons

112

b Fig.

39

Microstructure X1200.

o f Calcium-aluminate

a) S e c o n d a r y e l e c t r o n s b) T i t a n i u m X - R a y map

inclusion (Fi

c F i g . 40

Microstructure of spinel a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) M a g n e s i u m X - R a y map d) T i t a n i u m X - R a y map

d inclusion.

X600

114

F i g . 41

P i e c e o f u s e d Rammed l i n i n g .

XI

115

Fig.

42

T y p i c a l m i c r o s t r u c t u r e o f t h e r a m m e d l i n i n g 6cm f r o m t h e w o r k i n g f a c e . X20, Secondary electrons

116

F i g . 43

C r o s s s e c t i o n o f w o r k i n g f a c e o f rammed l i n i n g . X24 a) S e c o n d a r y E l e c t r o n s b ) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map d) T i t a n i u m X - R a y map e) N i c k e l X - R a y map

117

Fig.

44

I n c l u s i o n s f r o m rammed l i n i n g , I n t e r f a c e N i m o n i c 9 0 1 / rammed l i n i n g , X 8 0 , S e c o n d a r y E l e c t r o n s

118

F i g . 45

A l t e r e d r a m m e d l i n i n g (5mm f r o m i n t e r f a c e ) . Dark phase: s p i n e l ; gray phase: titanium rich; l i g h t phase: t i t a n i u m and c e r i u m r i c h . X400, Secondary Electrons

119

F i g . 46

U n a l t e r e d MgO g r a i n c l o s e t o w o r k i n g f a c e l i n i n g . X40, S e c o n d a r y E l e c t r o n s .

o f rammed

120

TABLES

OXIDE A1 0 2

C r

(h|

3

2°3

IN IRON 4. 3 X l O "

n

1. 1 X l O "

< Cr h

sio

2

(h

Ti0

2

(h .

s 1

!IN NICKEL

•

1. 5 X 1 0 "

4

1 4

8

ft

2. 2 X 10

•

2

h )

T ]

2. 2 X l O "

1 4

_5

1. 6 X 1 0

0

2. 8 X 1 0 '

- 6

6

2. 5 X 1 0 ~

6

3. 1 X l O "

8

0'

Mgo ( h

H g

3. 2 X 1 0 "

h ) o

TABLE I. S o l u b i l i t y p r o d u c t s and N i c k e l ( 3 )

of oxides

in iron

7

(2)

OXIDE

STEEL COMPOSITION OR ASSUMPTIONS

MgO

%C == 0.4%

P

%C == 0.4%

%Zr == 0 . 1 %

4.11 mm Hg

%c --= 0.4%

%A1 == 0 . 1 %

16.9

%Si == 0 . 2 5 %

1.95 a tm

Zr0

2

A1 0 2

Si 0

3

2

CaO

TABLE

= 0.4%

%c == 0.4%

CO

P

co •

Mg

Ca

PcO 3.86 mm Hg

mm Hg

0.68 mm Hg

2. P r e s s u r e s o f CO i n e q u i l i b r i u m w i t h d i f f e r e n t o x i d e s and s t e e l m e l t s a t 1600°C (From S c h a f f e r (10))

Ni

Al l o y

Si

Fe

Mn

Cr

Ti

Al

Co

Mo

B

Inconel

718

52.5

max. 0.06

max. 0.35

bal .

max. 0.35

19.

0.9

max. 0.6

max. 1.0

3.0

Inconel

X-750

bal.

0.04

0.3

7.0

0.7

15

2.5

0.9

0.5

0.3

limonic

Pk50*

bal.

0.03

max. 0.15

max. 2.0

max 0.1

19.5

3.0

1.4

13.5

4.2

0.007

901

bal

0.02 0.06

max. 0.4

bal

max 0.5

11.0 14.0

2.8 3.1

0.15 0.3

max. 1.0

5.0 6.5

0.01 0.02

bal

0.15 0. 20

max. 0.2

max 1.0

max 0.2

8.0 11.0

4.5 5.0

5.0 6.0

13, 17,

2 4,

0.01 0.02

Nimonic

l i m o c a s t Pk24 (IN 100)

*Simi1ar TABLE

3.

t o Was pa H o y Nominal

compositions

o f some Vacuum M e l t e d

Superalloys.

Zr

max. 0.003 0.03

max. 0.05

0.03 0.09

TABLE

4.

MATERIAL (REFRACT.)

Refractory SIZE OF FURN

ZIRCONIA or ALUMINA SILICA (KORUNDAL XD) or MAGNESITE -CHROME (GUIDON)

5. 2kg LAB.

MAGNEL or KORUNDAL XD

Practices

TYPE OF LINING

PRODUCTS

PRE-FIRED TO TEMP. OF BRICK MAKING OPERATION

D-979 A I S I 4340 A I S I 52100

27 ton PROD.

BRICK & MORTAR

LATROBE STEEL

MAGNESIA + ALUMINA (2%SiOj d.

200kg

RAMMED SINTERED (31600°C

Ni-base s uperal1oys Heat r e s . steels Aust n i ti c stee1s

ALUMINA -SILICA 95,60,42% A1 0

12kg

PRE-FIRED

%0.2C

2

3

n

II

LIFE AND/OR RESULTS

COMMENTS

A l l showed substanti al and c o m p a r able C losses both i n 1 s t & 2nd h e a t s . Oxygen c o n t e n t constant f o r each a l l o y .

Did not t r y K o r u n d a l XD w i t h 52100.

25-45

Backup l i n i n g : K o r u n d a l XD Working l i n i n g : K o r u n d a l XD Magnel

heats

heats

.".4 3

Decreasing Si pickup f o r d e c r e a s i ng Si 0 i n t h e 2

c r u c i b l e (and C cons.)

REFERENCE (28)

Some d e c r e a s e in C composition a f t e r 1st heat

MgO d e p l e t i o n i n t h e s u r f a c e and formation of sulphur r i c h 1 ayer

(29) ( 3 0 ) (31)

(22)

(24)

TABLE

4.

MATERIAL (REFRACT.)

(Cont'd) SIZE OF ' FURN.

TYPE OF LINING

PRODUCTS

MAGNESIA +ALUMINA (70/30)

7 ton

RAMMED WET/ GRAPHITE

Nickel alloys Stee1s (Carpenter Steel)

MAGNESIA

12kg

PROBABLY PRE-FlRE D

0.2%

ZIRCONIA (5% CaO)

15kg

?

MAGNESIA

Also 100kg

LIFE AND/OR RESULTS 30 h e a t s

Steel

NiMo 1.5 Alloy

COMMENTS

REFERENCE (33)

STEADY STATE 0_ 5 ppm 10 ppm Zr + Si p i ckup

(6)

(34)

Mg + Fe + S i pickup Al + S i pickup

ALUMINA FUSED LIME

20kg

RAMMED SINTERED @2000°C

N i - Fe Alloys

MAGNESIA + ALUMINA 65/25 6%S i 0

50/150 kg

RAMMED

Fe-C m e l t s

44 h e a t s o r mo re 8 cycles to room temp.

Very e f f e c t i v e S i d e - O x . and de-S

(35)

S t e a d y S t a t e 0^ 12 ppm

(11)

2

(NORTON RM 1170)

./cont'd

TABLE 4.

Cont'd SIZE OF FURN

TYPE OF LINING

MAGNESIA + ALUMINA Termax B3 Termax MG 10 ~75/20 5S i 0

350kg

RAMMED

SPINEL o r MAGNESIA or ALUMINA

10kg

MATERIAL (REFRACT.)

LIFE AND/OR RESULTS

PRODUCTS

COMMENTS

REFERENCE

Nickel Alloys (Mg/W) C deoxidation

(36)

0

Fe = Ni Ni-Fe-Mo Ni

For Pure I r o n b e s t de-Ox i n Alumina (3.6x 10-5 CxOJthen S p i n e l and then M a g n e s i a ( 1 6 x l O - C x 0)

(37)

5

Stee1s Superal1oys (Cameron I r o n )

MAGNEL

60t

BRICK & MORTAR

MAGNESIA

1 ton

RAMMED 20% Mo-Ni (PROBABLY) A l l o y Dai do Steel

MAGNESIA

250kg 5-10t

(38)

::

(39)

Hastel1oy R-235 RAMMED

FIRTH-BROWN

(40) F i r i n g with

template

(41)

TABLE 4.

Cont'd

MATERIAL (REFRACT.)

SIZE OF FURN

MAGNESIA or MAGNESIAALUMINA or ALUMINA

TYPE OF LINING

PRODUCTS

RAMMED

Fe,Ni

alloys

1501000 kg

RAMMED (?)

MAGNESIA

6t

RAMMED

MAGNESIA

300kg

RAMMED

Ni a l l o y s Steels (Jessop & Sons)

500kg

RAMMED

Steels (Ke1seyHayes C o . )

RAMMED

Steels Ni-Alloys

MAGNESIA ALUMINA (70/30)

MAGNESIA or MAGNESIAALUMINA (66/25)

COMMENTS

Spinel ~3 5 heats 250-1000kg Magnesi a h a l f of the 1i fe of S p i n e l

ZIRCONIA or MAGNESIA

MAGNESIA , ALUMINA (70/30)

L I F E AND/OR RESULTS

REFERENCE

F i r i n g with template or g r a p h i t e c o r e - S t r e s s e s i n MgO a r e large

N i a 11 oy s , Steels (Special M e t a l s , 1957)

(5)

(42)

12 h o u r d ry i n g

vacuum

Firing with graphite @. 2000°C i s p r e f e r r e d since i t allows the r e f r a c t o r y t o be checked before use.

(43) (44)

(45)

,

F i r i n g with template or g r a p h i t e c o r e . M a g n e s i a bonded by CaO + S i 0

(46)

2

M a g n e s i a - A l u m i n a by CaO + S i 0 + FeO 2

/conf d

TABLE 4. MATERIAL (REFRACT.)

Cont'd SIZE OF FURN.

TYPE OF LINING

KORUNDAL XD CORALBOND

BRICK and MORTAR

MAGNEL CORALBOND

BRICK and MORTAR

PRODUCTS

L I F E AND/OR RESULTS

REFERENCE

COMMENTS

7 heats of Ni-superal1oy Severe e r o s i o n i n the j o i n t s Better results than w i t h KORUNDAL XD CORALBOND

(47)

(47)

MAGNEL PE RIBON D

lot

BRICK and MORTAR

Stee1s (Armco Research)

15-20 h e a t s (Cyclic ope r a t i on)

Fai1ure occurs in the bottomTop l a y e r o f b r i c k s b u l g e s up. B a c k u p i s KORUNDAL XD

(48)

SPINEL BRICK or MAGNESITECHROMITE BRICK or ALUMINA BRICK

10 to 30t

BRICK and MORTAR

Stee1s,

20-45 h e a t s

MAG-CHROMITE b r i c k has 65%MgO/13% CrO /8%Al 0

(49)

ALUMINA or SPINEL

2.5t lOt 25t 60t

TYPE OF LINING BRICK and MORTAR

PRODUCTS

L I F E AND/OR RESULTS Good

COMMENTS

REFERENCE

Cement T a y l o r 3 4 1 * Back L i n i n g MULLITE BRICK w i t h N a S i 0 3

bonded s i l i m a n i t e (TAYLOR 320)

(50)

MATERIAL

C

Mn

Si

Cr

N i c k e l vac X - 7 5 0 *

0.067

0.08

0.04

13.55

A I S I 1095 (nomi na1)

0.96**

0.40

0.30

-

* Analysis **Analysed TABLE

5.

by T e 1 e d y n e - A l 1 vac a t UBC Composition

of metals

used i n the

tests

Ti

Al

Fe

Ni+Co

2.58

0.71

7.75

71.35

bal.

MATERIAL

MgO

Magne1

89..8

A 1

2°3 8. 3

Alundum 1139

99.

Alundum 1163

81.

Cora 1 bond P e r i bond 320

Taylor

341

Tasil

X

TABLE

6.

2

0. 7

P

2°5

-

0., 7 12.

C

a

0

F e

2°3

Others

-

0.,9

0.. 3

0., 1

0.. 1

Na 0--

0., 3

0.,4

1.. 3

Ti0 --

5. 3. 1

2

2

0., 1

79. 3

6., 7

9.1

0., 1

1.. 5

Ti0 --

78..8

2. 4

14., 7

-

0.. 1

0..8

A l k a l i e s - -2. 2

10.

-

0., 10

0.,10

A l k a l i e s - - 2 . 30

0..02

Taylor

S i 0

87. 95 .

0.. 1

55.

Typical chemical a n a l y s i s materials tested.

0..02 40.

0..03

4.5

-

2

0., 1

A l k a l i e s - - 2 ., 7

•1.0.

{% , a c c o r d i n g t o s u p p l i e r s )

of

refractory

OXYGEN CONTENT

MATERIAL SP2

17

MAGNEL

22

TAYLOR 341

28

PERIBOND

37

CAF

41

ALUNDUM 1139

46

CORALBOND

60

X-750 as

TABLE 7.

received

(PPM)

7

Oxygen c o n t e n t o f X-750 a f t e r 15 m i n . h o l d i n g t i m e a t 1500°C i n d i f f e r e n t refractory materials.