Cryogenic Toughness of SMA Austenitic Stainless Steel Weld Metals

Cryogenic Toughness of SMA Austenitic Stainless Steel W e l d Metals: Part II —Role of Nitrogen Optimum properties may be obtained if, in addition to being low in ferrite and carbon, the weld metal is low in nitrogen (under 0.05%), high in nickel (maximum permissible) and deposited with a lime-type electrode

BY E. R. SZUMACHOWSKI A N D H. F. REID

Introduction The role of delta ferrite in controlling toughness of austenitic stainless steel weld metals at cryogenic service temperatures was discussed in Part I of this study. 1 Data showed that toughness of many grades of stainless steel weld metals deposited by covered electrodes varied inversely with carbon and ferrite contents. Maximum toughness, as measured by Charpy Vnotch (CVN) impact energy properties and lateral expansion (LE), was obtained when both carbon and ferrite contents were as low as possible. This earlier work suggested that nitrogen might exert a greater influence on weld metal toughness than previously considered. The program, therefore, was expanded to include a study of the effect of specific ranges of nitrogen. Work was concentrated on Type 316L-15 and Type 16-8-2-15 grade-series. A few tests were made using Type 308-16 stainless steel electrodes. Procedure General test procedures followed those detailed in the earlier article. Charpy V-notch (CVN) specimens were used exclusively to develop CVN impact energy and lateral expansion values for weld metals tested at —200 F (-129 C), - 2 5 0 F (-157 C), and - 3 2 0 F (—196 C). All test specimens were prepared using covered electrodes. Validity of resultant data as related to other welding processes was not investigated. There were no metallo-

34-s i FEBRUARY 1979

Table 1 —Nitrogen Designations for Experimental Electrodes Suffix designation LN MN H\

Nominal range

Nitrogen content of w e l d metal, %

Low Medium

Less than 0.045 0.046/0.060 More than 0.061

High

graphic studies. To minimize welding variables, V» in. (3.18 mm) diameter core wire was used for virtually all of the tests. A common heat of core wire was used for all experimental electrodes of a specific stainless grade-series, which was defined as a group of compositions related to a specific grade of stainless steel. Composition of weld metals w i t h i n each grade-series was adjusted by additions of metal powders to the electrode covering. The same welder made all test specimens. Nitrogen content of a weld deposit was adjusted by selective additions of nitrogen-enriched metal powders to the electrode covering. The resultant weld deposits were subdivided according to nitrogen content—Table I.

Paper presented at the AWS 59th Annual Meeting held in New Orleans, Louisiana, during April 3-7, 1978. E. R. SZUMACHOWSKI is Director of Research and H. F. REID is Assistant Vice President, Technical Services, Welding Products Division, Teledyne McKay, York, Pennsylvania.

Variations in nitrogen content of weld metals w i t h i n a grade-series were accompanied by rebalancing of the chromium and nickel contents to permit comparison of properties w i t h in the same ferrite range. Composition and ferrite content of the experimental weld metals used in studying the effects of nitrogen are summarized in Table 2. Impact energy and lateral expansion values are summarized in Table 3.

Composition Evaluation Type 316L-15 Weld metals deposited by Type 316L lime-type stainless steel electrodes were one of the most promising gradeseries observed in Part I of this investigation. By chance, core wire chosen for the initial series permitted the preparation of weld metals w i t h nitrogen contents of less than 0.045%. In this study, these earlier compositions were designated " L N " alloys and compared with weld metals containing approximately 0.06% and 0.09% nitrogen, designated " M N " and " H N , " respectively, in accordance with Table I. The effects of nitrogen content of weld metals within similar ferrite ranges on lateral expansion at cryogenic temperatures are summarized in Fig. 1. At all test temperatures, rise in nitrogen content of weld deposit was accompanied by a sharp drop in weld metal toughness. When tested at —320 F (—196 C), lateral expansions of fully

Table 2—Experimental Weld Metal Corr positions and Ferrite Numbers Co n position of undiluted weld metal, %

Test no.

Mn

C

Si

P

S

755-MN 754-MN 148-LN 149-LN 150-LN""

0.057 0.054 0.052 0.048 0.049

1.62 1.65 1.19 1.19 1.13

0.38 0.35 0.35 0.32 0.41

0.022"' 0.022" 1 0.022 0.022 0.023

0.013 0.014 0.010 0.010 0.01 1

796-LN 771-LN 772-LN 773-LN'" 774-LN'" 1 065-MN1" 066-MN"" 067-MN'" 068-MN1" 061-HN 062-HN 063-HN 064-HN'"

0.039 0.038 0.038 0.037 0.038 0.033 0.032 0.035 0.029 0.033 0.033 0.033 0.030

2.27 2.32 2.37 2.27 2.26 2.54 2.52 2.51 2.64 2.44 2.42 2.42 2.46

0.31 0.36 0.33 0.38 0.37 0.27 0.35 0.30 0.32 0.30 0.34 0.29 0.31

0.036 0.031"' 0.031"' 0.031 0.031 0.020 0.021 0.021 0.019 0.022 0.023 0.022 0.020

0.007 0.007 0.007 0.007 0.008 0.006 0.006 0.006 0.006 0.005 0.006 0.006 0.007

810-LN'" 809-LN"" 787-LN 788-LN 789-LN'" 041-HN"" 040-HN"' 037-HN 038-HN 039-HN""

0.054 0.055 0.053 0.054 0.049 0.049 0.048 0.049 0.042 0.047

1.16 1.97 2.21 2.17 2.18 1.30 2.00 2.23 2.15 2.10

0.40 0.36 0.35 0.25 0.30 0.43 0.43 0.41 0.35 0.31

0.021 0.021 0.021 0.024 0.023 0.017 0.016 0.018 0.018 0.018

0.017 0.015 0.014 0.015 0.015 0.015 0.014 0.014 0.014 0.014

Cr

Ni

Type 308-16 9.84 19.53 10.40 18.81 19.69 10.02 10.35 19.13 18.91 11.29 Type 316L-15 18.97, 12.30 18.37 12.50 18.08 13.52 14.25 17.53 17.36 16.70 17.82 11.98 17.81 12.61 12.90 17.80 17.74 15.60 18.22 11.63 17.91 12.50 17.57 13.03 15.48 17.36 Type ' 6-8-2-15 17.70 8.80 8.74 16.68 15.24 9.09 15.31 9.19 11.47 15.00 8.75 17.82 8.72 17.82 9.19 15.33 9.36 15.28 11.52 14.93

Ferrite no., FN 1

Mo"'

N "'

0.20 0.20 0.13 0.12 0.13

0.059 0.059 0.042"" 0.044"" 0.044""

— -

9.0 5.6 2.5

4.0 1.8 7.7 5.4 0.1

'4.4 0.8 6.8 3.8 1.5

2.28"" 2.29"1' 2.22"" 2.23"" 2.15"" 2.28"" 2.19"" 2.25"" 2.12"" 2.29"" 2.18 d ' 2.18"" 2.14""

0.033 0.033 0.032"" 0.033"" 0.033 0.059"" 0.056"" 0.054"" 0.052"" 0.091 ,d ' 0.096 "" 0.095"" 0.091""

7.6 4.5 0.6 0.8 0.3 5.5 0.8 0.3 0.3 1.1 0.3 0.3 0.3

7.2 4.8 0.8 0.1 0.1 5.4 1.8 0.4 0 1.8 0.2 0 0

6.0 3.5 -0.2 -3.0 -9.1 0.7 -0.5 -1.3 -7.0 -2.8 -3.8 -8.5 -13.2

1.69"" 1.69"" 1.66"" 1.67"" 1.60"" 1.69"" 1.72"" 1.70"" 1.73"" 1.64""

0.042"" 0.039"" 0.038 0.038 0.033"" 0.072"" 0.082"" 0.079"" 0.081"" 0.071""

9.1 5.2 1.5 1.4 0 8.2 3.1 1.4 0.6 0.3

9.9 5.8 2.0 2.0 0 7.1 3.2 0.8 0.6 0

9.0 3.8 -2.3 -2.6 -8.3 7.3 5.7 -4.0 -4.4 -11.0

Meas'd. "

Meas'd."''

Calc'd

'^'Except as n o t e d , all values were estimates. '"Average M a g n e Cage measurement o n surface of groove w e l d . " ' A v e r a g e M a g n e Gage measurement o n surface of pad of u n d i l u t e d w e l d metal used for analysis. " " A c t u a l values. " O u t s i d e of A W S A5.4-69 chemistry range. " C a l c u l a t e d value.

austenitic " H N " deposits were less than 25% that of their " L N " counterparts. In a like manner, increased nitrogen content of w e l d metal adversely affected lateral expansion over the full range of ferrite numbers investigated. Figure 2 summarizes the effect for tests

50

1

I

l

l

l

l

l

made at - 3 2 0 F (-196 C). The pattern of curves at other test temperatures parallels those of the - 3 2 0 F (-196 C) tests. The effects of increased nitrogen on CVN impact energy values at all test temperatures duplicated trends o b served in the lateral expansion data.

l

l

l

Legend

Legend

•

45

LN at - 3 2 0 F . - 1 9 6 C

•

MN at - 3 2 0 F . - 1 9 6 C HN at - 3 2 0 F . - 1 9 6 C

40 35

-

-

'

-

1

£ 40

ut

= 30 c

-

aj J

_ 20

Type 316L-15 M N (-1.3 F N ) Type 316L-15 HN (-3.8 F N )

_

*—~^^ \ ~^~~~^

\

15 10

^ ^ A

5 0

Type 3 1 6 L - 1 5 L N (-3.0 F N )

-

-25 UJ

Marked reductions in impact energy values accompanied increased nitrogen content in the w e l d metals. Data for tests made at - 3 2 0 F ( - 1 9 6 C) are summarized in Fig. 3. Graphs of data for tests made at the higher test temperatures f o l l o w e d similar patterns.

i

i

i

i —6

i

i — 4 — 2

% \>

-

^

I

0

I

I

I

2

Calculated Ferrite Number. FIM

Fig. 1—Effect of nitrogen on lateral expansion of Type 316L-15 weld metals

-250 Testing T e m p e r a t u r e .

Fig. 2—Lateral expansion ol Type 3I6L-I5 various amounts ol ferrite and nitrogen

-200 F

weld metals containing

W E L D I N G RESEARCH S U P P L E M E N T I 35-s

Table 3—Properties of Exper mental Weld Metals

Test no.

Charpy V-notch (CVN), ft-lb at

Calculated Ferrite, FN

-200 F

755-MN 754-MN 148-LN 149-LN 150-LN

4.4 0.8 6.8 3.8 1.5

20.4 24.6

796-LN 771-LN 772-LN 773-LN 774-LN 065-MN 066-MN 067-MN 068-MN 061-HN 062-HN 063-HN 064-HN

6.0 3.5 -0.2 -3.0 -9.1 0.7 -0.5 -1.3 -7.0 -2.8 -3.8 -8.5 -13.2

38.0 34.7 45.3 53.7 63.3 31.8 38.5 37.6 48.4 32.3 33.5 37.3 40.9

810-LN 809-LN 787-LN 788-LN 789-LN 041-HN 040-HN 037-HN 038-HN 039-HN

9.0 3.8 -2.3 -2.6 -8.3 7.3 5.7 -4.0 -4.4 -11.0

29.8 30.1 31.6 33.2 36.8 27.0 29.9 31.0 29.1 35.9

-250 F

-

1

1

Legend •

-320 F

Type 308-16 16.4 13.6 21.1 18.5 17.8 20.1 28.4 Type 316L-15 27.5 19.5 26.0 21.2 39.3 33.0 50.6 43.1 60.5 55.4 26.2 22.1 34.4 25.3 46.0 30.6 43.9 37.1 25.5 17.8 30.8 22.9 36.8 25.3 36.6 30.1 Type 16-8-2-15 25.0 22.6 26.5 24.0 29.4 27.0 29.4 26.5 34.9 29.6 20.7 24.5 25.8 22.3 26.2 21.1 25.0 23.3 31.5 23.6

t

Lateral expansion, mils at -200 F

-250 F

-320 F

13.3 17.7

9.8 16.0

-

-

6.3 11.0 8.3 10.7 18.3

29.3 28.7 37.0 44.3 56.3 20.0 27.0 26.0 36.0 18.7 21.3 24.3 27.7

22.3 18.7 32.0 41.7 54.3 15.0 25.7 31.0 31.0 11.7 16.3 23.0 24.3

12.0 14.3 23.7 34.0 45.0 10.3 13.7 18.3 22.0 5.0 9.3 11.0 14.7

21.3 2.3.0 27.3 27.0 31.0 15.7 17.3 20.7 20.3 27.3

17.0 21.0 24.0 23.3 27.7 12.0 13.7 16.3 15.0 19.7

17.0 18.0 24.0 20.7 23.3 9.0 10.7 12.3 12.0 13.7

i

i

I

•

yp

'

p

SUM -

1fi

l

N

•

'

i

i

i

Calculated Ferrite Content. FN

Fig. 3—Charpy V-notch energy of Type 316L-15 weld metal containing various amounts ol ferrite and nitrogen after testing at —320 F (—196 C) Type 16-8-2-15 Grade-Series W e l d metals of the Type 16-8-2 grade-series were another very promising group as described in the earlier paper. These promising compositions also contained less than 0.045% nitrogen and thus fitted into the " L N " designation of Table 1. Additional Type 16-8-2-15 electrodes were prepared as shown in Table 2. Nitrogen contents of weld metals of this new series, designated " H N " , were approximately double those of the initial

36-s I FEBRUARY 1979

Type 308-16 Grade-Series If good toughness properties can be damaged by increased nitrogen content of the weld metal, is the reverse true? In Part I, weld metals deposited by Type 308-16 grade-series electrodes exhibited some of the poorest toughness properties observed in this investigation. In these additional compositions, nitrogen content was reduced from approximately 0.06% in the initial grade-series to less than 0.045% for a special low nitrogen (LN) series. Material availability made it necessary to change diameter of the core wire. The three experimental electrodes of the Type 308-16 LN gradeseries (Table 3) were made using %a in. (4.0 mm) diameter wire instead of the standard Va in. (3.2 mm) diameter core wire. Low temperature lateral expansion characteristics of weld metal deposited by Type 308-16 LN electrodes were improved by the 25% reduction in nitrogen content—Fig. 7. At —320 F (-196 C) a 308-16 LN weld metal w i t h 1 FN had a lateral expansion that met minimum Code requirements and was about 50% tougher than the original medium nitrogen content weld metal.

Discussion of Results

\ T

nitrogen content of the weld metals increased—Figs. 5 and 6, respectively. Data from tests at - 2 5 0 F (-157 C) and - 2 0 0 F (-129 C) parallel the - 3 2 0 F (-196 C) results. It was of particular interest that curves for the high nitrogen versions of 16-8-2 weld metals exhibited the same nearly flat line or minimal slope characteristics observed earlier w h e n testing the lower nitrogen content alloys.

compositions. Over the range of temperatures investigated, increased nitrogen content of the weld metal was accompanied by a drop in toughness as measured by lateral expansion —Fig. 4. The decrease at any test temperature, however, was not as great as that observed for Type 316L stainless steel weld metals. W i t h i n the ferrite range investigated, CVN impact energy values and lateral expansion both decreased as

Data in the preceding paragraphs indicated that nitrogen was the potent force that earlier data intimated. The full implications of this finding remained to be evaluated. Regression Analysis The initial underlying assumption of this project was that, in some fashion, cryogenic toughness of weld metals deposited by covered electrodes w o u l d be inversely related to delta ferrite content in the weld metal. Lower ferrite contents generally resulted in improved toughness values. Reductions in ferrite content resulted from increases in carbon, nickel, manganese, and/or nitrogen. From the outset, it was apparent that carbon generally affected impact energy values adversely. The data confirmed that nitrogen also decreased cryogenic

toughness. This suggested a need to analyze the experimental data on a compositional basis rather than on the basis of delta ferrite content alone. This approach also was more compatible for evaluating weld metals containing no ferrite. Linear regression was employed to fit equations for the 62 compositions shown in Table 4. This summary of compositions includes most of those reported in Part I plus some six compositions not otherwise reported. Some compositions appearing in Part I and the earlier section of this report were not available at the time the regression analysis was made. The regression analysis was used to find the best fitting co-efficient, A,, that would relate CVN lateral expansion or impact energy at —320 F (—196 C) to composition by linear models of the following form: Mils (or ft-lb) = A, + A, (%C) + A3 ( M n ) + A., (%Cr) + A5 (%Ni) + A e (%Mo) + A7 (%N) + As (coating type). It was recognized that available data did not fit the classic pattern of a regression analysis study. Variables were not totally independent but represented normal interrelationships of stainless steel filler metal compositions. Despite this inherent handicap, it was felt that regression analyses w o u l d provide useful information. Silicon was deliberately not included as a compositional variable in developing the models because the range of silicon variation was very small. An effect for electrode coating type was included because it had been suggested, as noted earlier, that the DC-Lime (—15)-' coverings produce

Legend _ , Type 16-8-2-15 LN •

-300

-200

Testing Temperature, F

Fig. 4—Effect of nitrogen on lateral expansion of Type 16-8-2-15 weld metals

measure of the degree of confidence placed in the significance of each specific effect. A ratio of 2 or more indicated high confidence while a ratio of less than 1 indicated very little confidence. The regression analysis further indicated variables that are confounded w i t h one another (i.e., variables that were not independent of one another insofar as their levels are concerned). Regression analysis further provided an estimate of the error to be expected

cleaner weld metal than that deposited by high titania (—16) coverings. For simplicity, the values —15 or —16 were arbitrarily assigned as the coating variable "levels." However, it must be recognized that the coating variable represents only t w o discrete values, not a c o n t i n u u m of values as the other variables. Regression analysis also provided a standard error for each effect. The ratio of the absolute value of the effect to the standard error provided a

1

=

Type 16-8-2-15 HN

_L -250

_l_ -350

(

I

1

1

3 0--

> o CJl

X

c

X

X

X

o 20 CO

Legend

10 -12

•-

a

Type 16-8-2-15 LN

X—

x

Type 16-8-2-15 HN

i - 8

I 12

—4

Calculated Ferrite Content, FN Fig. 5—Charpy V-notch energy of Type 16-8-2-15 weld metals containing various amounts of ferrite and nitrogen tested at —320 F (—196 C)

W E L D I N G RESEARCH SUPPLEME NT I 37-s

24

1

1

1

1

1

1

i

1

1

1

1

-

22

•

\.

20

V

18

^*~~~--~-_ -

-

I'4 -

-

« 16

5 c

ra a io

_ "ra a) 10 ra _i

8

—~__0

-

o —

-

_

-

\. -

Legend

"

6 #

1 N

at

_i?nF

-iQfir

-

4 0

HN at -3?rjF

-196C

-

2

i

0

—12

I I I I I -10 — 8 — 6 - 4 - 2

0

1

1

1

2

4

6

1 8

I 10

Calculated Ferrite Number. FN

Fig. 6—Lateral expansion of Type 16-8-2-15 weld metals containing various amounts of ferrite and nitrogen

in applying the model to predict the response (either lateral expansion or energy absorption) and the extent to which the model explains all of the variations in responses observed. Regression analysis of lateral expan-

sion data is summarized in Table 5. The resultant models are: For Lime-Type XXX-15 Electrodes. Lateral Expansion (CVN), Mils = 79.00 -133.8 (%C)-0.20 (%Mn)-1.13 (%Cr) + 1.72 (%Ni) - 2.34 (%Mo) -

177.2 ( % N ) - 1 5 (2.83) For Titania-Type XXX-16 Electrodes. Lateral Expansion (CVN), Mils = 79.00 -133.8 (%C)-0.20 (%Mn)-1.13 (%Cr) + 1.72 (%Ni) - 2.34 (%Mo) 177.2 ( % N ) - 1 6 (2.83) These models may be simplified by subtracting the coating variable from the primary intercept value. Data indicated a high degree of confidence in the nickel, carbon, chromium, and nitrogen values. The overall effect of molybdenum and coating type were less positive. The role of manganese in influencing lateral expansion at —320 F (—196 C) was very unclear. The models explained 74% of the observed lateral expansion values. Standard deviation was ± 6.5 mils ( ± 0.17 mm). Regression analysis of CVN data is summarized in Table 6. The resultant model equations, after incorporating the coating variable, parallel the lateral expansion formulae w i t h changes in value of specific factors as follows: For Lime-Type XXX-15 Electrodes (coating variable subtracted). Impact Energy (CVN), ft-lb = 31.15 - 175.8 (%C) + 0.42 (%Mn) - 0.90 (%Cr) + 2.16 (%Ni) - 1 1 1 . 3 (%N) For Titania-Type XXX-16 Electrodes (coating variable subtracted). Impact Energy (CVN), ft-lb = 27.70 - 175.8 (%C) + 0.42 (%Mn) - 0.90 (%Cr) -I2.16 (%Ni) - 1 1 1 . 3 (%N) The data indicated strong levels of

20 18 16 14 u>

I-

12

_ g '(/>

a 10 a x

UJ

_j

8

3 75 Legend -»Type 308-16 (st'd alloy)

4 -

-xType 308-16 LN 2 -

1

8

Calculated Ferrite Number, FN Fig. 7—Lateral expansion ol Type 308-16 weld metals containing various amounts of ferrite and nitrogen tested at —320 F (—196 Q 38-s I FEBRUARY 1979

Table 4—Compositions Used for Development of Regression Analysis Formulae Propei ties at - 3 2 0 F (-196 C) Composition of undiluted w e l d metal, %

Test

no.

C

Mn

783 784

0.054 0.062

2.15 2.13

0.30 0.32

20.32 20.14

755 754 821 822 823

0.057 0.054 0.055 0.056 0.056

1.62 1.65 2.26 2.22 2.25

0.38 0.35 0.36 0.32 0.25

19.53 18.81 21.12 19.76 19.45

791 792 793 794 795

0.0.36 0.035 0.032 0.034 0.034

1.34 1.36 1.34 1.35 1.70

0.31 0.35 0.30 0.29 0.35

19.99 19.20 18.83 18.69 18.99

752 764 753 763 824 825 826

0.034 0.027 0.026 0.026 0.0.32 0.033 0.030

1.00 0.97 0.97 0.92 1.15 1.17 1.10

0.39 0.39 0.42 0.38 0.41 0.32 0.32

20.19 19.51 18.99 18.20 20.68 19.65 18.50

842 843 844

0.072 0.074 0.102

1.75 1.86 2.20

0.45 0.49 0.42

23.88 23.20 23.15

767

0.070

1.95

0.47

18.10

796 771 772 773 774 065 066 067 068 061 062 063 064

0.039 0.038 0.038 0.037 0.038 0.033 0.032 0.035 0.029 0.033 0.033 0.033 0.030

2.27 2.32 2.37 2.27 2.26 2.54 2.52 2.51 2.64 2.44 2.42 2.42 2.46

0.31 0.36 0.33 0.38 0.37 0.27 0.35 0.30 0.32 0.30 0.34 0.29 0.31

18.97 18.37 18.08 17.53 17.36 17.82 17.81 17.80 17.74 18.22 17.91 17.57 17.36

756 757 765 766

0.033 0.032 0.029 0.031

2.02 2.06 2.18 2.36

0.48 0.46 0.40 0.47

19.55 18.54 18.28 17.96

810 809 787 788 789 041 040 037 038 039

0.054 0.055 0.053 0.054 0.049 0.049 0.048 0.049 0.042 0.047

1.16 1.97 2.21 2.17 2.18 1.30 2.00 2.23 2.15 2.10

0.40 0.36 0.35 0.25 0.30 0.43 0.43 0.41 0.35 0.31

17.70 16.68 15.24 15.31 15.00 17.82 17.82 15.33 15.28 14.93

838 839 840 841

0.055 0.054 0.053 0.055

2.26 7.25 2.12 2.17

0.48 0.44 0.37 0.37

18.97 18.44

057

0.123

2.25

0.62

26.40

785

0.128

2.06

0.44

26.30

Cr

Mo

Ni Type 308-15 11.26 11.31 Type 308-16 9.84 10.40

Impact energy, ft-lb

Lateral expansion, mils

0.20 0.20

0.056 0.072

14.3 20.2

8.7 14.0

0.20 0.20 0.20 0.20 0.20

0.059 0.059 0.082 0.082 0.082

13.6 18.5 9.4 12.0 15.3

6.3 11.0 3.3 4.7 9.0

0.06 0.06 0.06 0.06 0.06

0.071 0.071 0.071 0.071 0.088

19.0 21.9 23.3 24.3 25.5

12.0 14.0 17.7 17.0 16.3

9.99 10.01 10.10 10.07 10.10 10.22 10.45 Type 309-15 13.22 13.57 13.32 Type 316-16

0.13 0.13 0.13 0.13 0.04 0.04 0.06

0.065 0.064 0.066 0.065 0.089 0.089 0.089

12.0 14.8 17.8 23.8 13.3 18.3 22.4

5.7 7.3 11.3 14.3 7.3 10.3 17.0

0.27 0.27 0.27

0.064 0.070 0.070

9.9 9.9 14.9

2.3 2.7 6.7

14.30 Type 316L-15 12.30 12.50 13.52 14.25 16.70 11.98 12.61 12.90 15.60 11.63 12.50 13.03 15.48 Type 316L-16 12.51 12.54 13.88 14.15 Type 16-8-2

2.24

0.052

40.5

26.3

2.28 2.29 2.22 2.23 2.15 2.28 2.19 2.25 2.12 2.29 2.18 2.18 2.14

0.033 0.033 0.032 0.033 0.033 0.059 0.056 0.054 0.052 0.091 0.096 0.095 0.091

19.5 21.2 33.0 43.1 55.4 22.1 25.3 30.6 37.1 17.8 22.9 25.3 30.1

12.0 14.3 23.7 34.0 45.0 10.3 13.7 18.3 22.0 5.0 9.3 11.0 14.7

2.20 2.26 2.25 2.26

0.035 0.035 0.035 0.054

8.9 15.3 23.6 40.5

3.3 8.7 17.3 28.3

1.69 1.69 1.66 1.67 1.60 1.69 1.72 1.70 1.73 1.64

0.042 0.039 0.038 0.038 0.033 0.072 0.082 0.079 0.081 0.071

22.6 24.0 27.0 26.5 29.6 20.7 22.3 21.1 23.3 23.6

17.0 18.0 24.0 20.7 23.3 9.0 10.7 12.3 12.0 13.7

1.64 1.62 1.65 1.66

0.043 0.042 0.042 0.042

23.8 21.6 20.0 25.3

11.7 11.3 12.7 20.3

0.03

0.059

38.7

28.3

0.14

0.092

28.1

19.7

9.50 9.76 10.74 Type 308L-15 10.25 10.30 11.69 11.82 13.70 Type 308L-16

75

17.05 14.75

8.80 8.74

9.09 9.19 11.47 8.75 8.72 9.19 9.36 11.52 Type 16-8-2-16

8.60 8.73 8.65 9.05 Type 310-15 21.55 Type 310-16

21.33

Continued

on next

page

WELDING RESEARCH SUPPLEME NT I 39-s

Table 4--Compositions Used for Development of Regression Analysis Formulae--Continued Propert es at - 3 2 0 F (- -196 C) Test no.

Mo

N

I npact e nergy, ft-lb

0.3 0.3 0.3 0.25 0.24

0.033 0.033 0.033 0.034 0.034

42.1 40.4 65.2 71.3 71.0

35.0 30.0 52.7 54.0 57.0

1.78

0.039

28.4

22.3

Composition of undiluted weld metal, % Cr

C

Mn

Si

775 776 777 085 086

0.210 0.208 0.150 0.130 0.140

3.40 4.80 4.80 2.64 2.24

0.57 0.55 0.57 0.54 0.60

8.38 18.42 18.13 17.82 . 17.80

790

0.224

1.98

0.43

15.22

Ni Type 330-15 34.40 34.42 34.22 34.10 34.19 Type 330-16 34.20

Table 5—Regression Analysis Results for Mils Lateral Expansion Model When Tested at -320 F (-196 C)

Parameter A, A, A., A4 A5 A6 A, A8

(intercept) (effect of C) (effect of Mn) (effect of Cr) (effect of Ni) (effect of Mo) (effect of N) (effect of coating)

Best parameter estimate

Standard error of parameter estimate

Ratio of best parameter estimate to standard error

79.0 -133.8 -0.20 -1.13 1.72 -2.34 -177.2 -2.83

±30.8 ±39.3 ± 1.73 ± 0.43 ± 0.25 ± 1.26 ±48.7 ± 1.85

2.56 3.40 0.12 2.62 6.91 1.86 3.64 1.53

Table 6—Regression Analysis Results for CVN Energy Absorption Model When Tested at -320 F (-196 C)

Parameter A, A2 A3 A4 A5 As A, A8

(intercept) (effect of C) (effect of M n ) (effect of Cr) (effect of Ni) (effect of Mo) (effect of N) (effect of coating)

Lateral expansion, mils

values. A lesser degree of confidence was shown for the effects of changes in chromium, nitrogen, and coating type. The roles of manganese and molybdenum were unclear. These model equations explain 75% of the changes in CVN observed. Standard deviation was ± 7.6 ft-lb ( ± 10.3 J). A matrix of correlation coefficients for both models, not included in this paper, confirmed that the effects of nickel, carbon, and manganese were confounded significantly. In a like manner, the effects of chromium and molybdenum were shown to be significantly interrelated. Accuracy of Predictions

Best parameter estimate

Standard error of parameter estimate

Rat o of best parameter estimate to standard error

82.9 -175.8 0.42 -0.90 2.16 -0.80 -111.3 -3.45

±36.3 ±46.3 ± 2.04 ± 0.51 ± 0.29 ± 1.48 ±57.3 ± 2.18

2.29 3.80 0.21 1.78 7.38 0.54 1.94 1.59

Lateral expansion of each of the 62 alloy compositions used to develop the model equations was calculated in accordance w i t h the regression analyses formulae. As expected, predicted and measured values did not always agree. W i t h i n the range of —2FN to + 2FN, agreement was nearly perfect. For higher ferrite content compositions, predicted values generally were higher than actual measurements. As the compositions became more strongly austenitic, the reverse was true, as illustrated in Fig. 8 which is a plot of values for the Type 316L-15 grade-series. Correlation between predicted and measured values for the Type 16-82-15 grade-series (Fig. 9) was better than that observed for any other grade-series investigated. Effect of Composition

Calculated Ferrite Number, FN Fig. 8-Lateral expansion of Type 316L-15LN weld metal predicted by regression analysis formula vs. actual measurements after testing at -320 F (—196 C) 40-s I FEBRUARY 1979

The regression analysis formulae summarized the role of each element in influencing weld metal toughness at - 3 2 0 F (-196 C). In addition, the formulae provided a tool for developing balanced compositions w i t h optimized toughness properties. W e l d metal compositions outlined in AWS Specification A5.4-69 were

selected for a number of reasons, including corrosion resistance, long before any major consideration was given to toughness of weld metal at cryogenic temperatures. In recent years, the ranges for many grades have been made even more restrictive by commercial design specifications requiring that final welds shall have a minimum ferrite content of at least 3FN. Dual weld metal requirements for 3FN min. and 15 mils (0.38mm) min. lateral expansion at - 3 2 0 F (-196 C) are at odds and sharply limit the choice of welding filler metal compositions conforming to the requirements of AWS A5.4 or ASME SFA 5.4. Fabricators rely strongly on controlled amounts of ferrite in stainless steel weld metals to maximize crack resistance. At the same time, the improved impact properties of fully austenitic weld metals should not be ignored for cryogenic applications. For such service, it is necessary to mesh these two composition requirements to produce deposits that are both structurally sound and tough at cryogenic service temperatures. All grades of fully austenitic weld metal are not necessarily suspect. Despite the presence of microfissures, fully austenitic stainless steel welds have been used successfully for many years. ASME procedure qualifications and MlL-E-0022200/1 electrode specifications recognize their presence by

40

I

I

I

I

content,

tn

e o V)

__20 X UJ

*~==^—-_-—_____x

-

% 0.035 0.045 0.055

—

0.035 0.045

— —

0.035 0.045 0.055 0.065

—

0.035 0.045 0.055

—

0.035 0.045 0.055 0.065

25.5 23.4 20.9 19.6

0.035 0.045 0.055 0.065

22.7 20.6 18.8 16.8

-I FN

I FN

9 « £ 10

Legend

_

u

Analysis

t

-10

- 8

i

l

—6

l

1 4

i

• 4 - 2

0

2

1 10

8

6

Calculated Ferrite Number. FN

Fig. 9—Lateral expansion of Type 16-8-2-15LN weld metal predicted by regression analysis formula vs. actual measurements after testing at —320 F (—196 C)

permitting a specified number and size of fissures in bend test specimens. Filler metal manufacturers consistently meet these requirements by proper control of weld metal compositions. Dual requirements for both toughness and ferrite place added importance on raw material selection by the electrode manufacturer. Based on the data presented in this study, low carbon and low nitrogen content weld metals are the essential requirements for most grades for attaining compositions w i t h good lateral expansion at cryogenic temperatures. This was particularly true for weld metal compositions containing some ferrite. Carbon and nitrogen contents normally increase from initial contents of core

3 FN

Type 308-15 (77% nickel) 19.3 17.2 15.4 Type 308-16 (77% nickel) 16.5 —