other properties. On the other hand, titanium alloys exhibit high strength ..... Table 5:Difficulties in cutting and shearing titanium and countermeasures. Difficulties.
Ti-10V-2Fe-3Al (STA) Ti-6Al-2Sn-4Zr-6Mo (STA) Ti-15V-3Cr-3Sn-3Al (STA)
1000 Ti-6Al-4V (Ann) KS120
800
Ti-9 (Ann)
KS100
Ti-15Mo-5Zr-3Al (STA)
KS85
600 KS70 Ti-3Al-2.5V
KS50
400
300
20
Ti-15V-3Cr-3Sn-3Al (ST)
250
1600
Steel-nickel alloy
Aluminum alloy
0
Ti-6Al-4V ELI (ST)
1400
10
Commercially pure titanium 0
Magnesium alloy
200
400
600
800
1000
Temperature (˚C)
1200 1000
Ti-5Al-2.5Sn ELI
200
800
Fig.2:Specific strength of various materials 600
Titanium alloy
0
Table 1:Representative characteristics of commercially pure titanium, titanium alloys, and steel base materials (Plate materials)
600
KS50 KS70 Ti-6Al-4V Ti-3Al-2.5V Ti-15V-3Cr -3Sn-3Al Mild steel Stainless steel (SUS 304)
0.2% yield strength (MPa) 238
332
45.9
L
181
337
48.2
T
272
387
41.6
L
222
391
38.7
T
429
551
26.0
L T
411 888
545 957
25.9 10.1
L
905
959
10.3
T
615
661
23.0
L
501
654
20.0
T
789
828
19.8
L
772
823
19.1
T
169
303
45.0
L
167
301
46.5
T
263
648
58.0
L
264
662
55.7
117
-200
-100
-50
0
50
11.2
144
10.3
202
6.9
100
200
300
400
500
600
Portions 60
320
-
240
-
1400
50
1200
600 400 200 0
100
200
300
400
500
40
7.9
88
10.1
1.0 1.0 1.0 1.0 3.0 3.0
800
30
600
Ti-15V-3Cr-3Sn-3Al (ST)
Temperature (˚C) 20
Ti-5Al-2.5Sn ELI
600
400
10 40 0
-300
20 0
0
100
200
300
400
500
200
Ti-6Al-4V ELI(ST)
-250
-200
-150 -100 Temperature (˚C)
-50
0
50
600
0 1.0E+03
Temperature (˚C)
Fig.3:Tensile characteristics of various commercially pure titaniums, various titanium alloys and SUS304 under room temperature and high temperatures
titanium alloys. The specific strength of titanium alloy is superior to other metallic materials in the temperature range up to 600ûC. (Fig. 2) High temperature characteristics
Commercially pure titanium is stable for use in the temperature range up to approximately 300ûC due to its specific strength, creep resistance, and other properties. On the other hand, titanium alloys exhibit high strength in the temperature range up to approximately 500ûC. (Fig. 3)
1.0E+04
1.0E+05
1.0E+06
1.0E+07
Repetition frequency [-]
13.0
Commercially pure titanium has a tensile strength ranging from 275 to 590 MPa, and this strength is controlled primarily through oxygen content and iron content. The higher the oxygen and iron content, the higher the strength. We are currently producing various titanium alloys from Ti3A1-2.5V with a tensile strength of 620 MPa, to Ti-15Mo-5Zr-3AI with a tensile strength of 1250 MPa. (Tensile strengths listed above are KOBELCO's specified minimum values.) Fig.1 shows the tensile strength and yield strength of commercially pure titanium and various titanium alloys and Table 1 shows the tensile characteristics of commercially pure titanium and representative
0 -1 0 -1 0 -1
1000
60
260
Stress ratio Notch coefficient
Base material Base material Welded portion Welded portion Base material Base material
Commercially pure titanium (KS50)
800
80
168
Fig.5:Fatigue characteristics of commercially pure titanium (KS50) base material and welded portion
70 0
1000
0
10
Ti-1.5Al
KS50
200
-150
Temperature (˚C)
Vickers Erichsen Tensile hardness value strength Elongation (%) (Hv) (mm) (MPa)
T
-250
7
10
Repetition frequency
Temperature (˚C)
1200
0.2%yield strength(MPa)
KS40
Tensile direction
0 -300
SUS304
KS70
400
0
Elongation(%)
Material
Ti-6Al-4V (Ann)
800
6
5
10
200
1000
Representative values
150
Ti-15V-3Cr-3Sn-3Al (STA)
1200
Tensile strength(MPa)
Fig.1:Tensile strength of commercially pure titaniums and various titanium alloys, and 0.2% yield strength(Specified minimum values)
Commercially pure titanium (KS50)
400
1400
Stress (MPa)
Commercially pure titanium
Commercially pure titanium
1800
Titanium alloy
KS40
200
Titanium alloy
Base material Welded portion(400˚C x 300min annealing) Heat-affected zone(400˚C x 300min annealing)
2000
Elongation(%)
Tensile strength, 0.2%yield strength (MPa)
1200
30
Stress (MPa)
Tensile strength 0.2%yield strength
Tensile strength(MPa)
1400
Specific strength [0.2% yield strength/density] (kgf/mm2 /g/cm3)
MECHANICAL PROPERTIES
Fig.4:Low temperature tensile properties of commercially pure titanium and various titanium alloys
Low temperature characteristics
Neither commercially pure titanium nor titanium alloys become brittle even at extremely low temperatures. In particular, commercially pure titanium and Ti-5A1-2.5Sn EL1 can be used even at 4.2 K (-269ûC). (Fig. 4) Fatigue characteristics 7
The fatigue strength (10 cycles) is roughly equivalent to 50% of the tensile strength, and welding does not cause a significant decline in fatigue strength. (Figs. 5 and 6) In addition, even in seawater, both commercially
Fig.6:Fatigue characteristics of Ti-6Al-4V base material and welded portion
pure titanium and titanium alloys exhibit almost no decline in fatigue strength. The fracture toughness of titanium alloys range from 28 to 108MPa.m1/2 and is in negative correlation with tensile yield strength. Fracture toughness is dependent on microstructure, and thus fracture toughness is higher in materials with acicular structures. Toughness
CORROSION RESISTANCE
Zirconium
Commercially pure titanium
Material
Hastelloy C
AKOT
1
Ti-0.15Pd
0.1
Monel
Purity of sea water
0.01
Environment 0
2
4
6
Oxidizing
Non-oxidizing Fig.7:Corrosion resistance range of various metals (Each metal shows excellent corrosion resistance in the arrow-marked range)
8
10
12 Non-aqueous solution
HCl (mass %)
Fig.8:Corrosion resistance of commercially pure titanium and corrosion resistant titanium alloys in hydrochloric acid solution Aqueous solution
Commercially pure titanium
1
104ûC
0.8 Aluminum brass
0.6
90/10 cupronickel 0.4
54ûC
0.1
PdO/TiO2 coated titanium
150
Ti-6Al-4V
Brine
High strength titanium alloy
316 Stainless steel
304 Stainless steel
50
60
0.001
0.01
NaOH (mass %)
Fig.9:Corrosion rate of commercially pure titanium deaerated NaOH solution
Fig.11:Sand erosion resistance of commercially pure titanium and copper alloys in running sea water
High strength titanium alloy High strength titanium alloy
Velocity: 2.4 ~ 3.9m/sec Temperature: 10 ~ 27˚C Activated condition
50
40
Commercially pure titanium 5 10 15 Sand content in seawater (g/l)
0
High temperature and high pressure Commercially pure titanium bromide solution
100
0
0
Fuming red nitric asid
Cadmium Mild steel/Cast iron Low alloy steel Austenitic nickel cast iron Aluminum bronze Naval brass, bronze, red brass
Immune to crevice corrosion
32ûC
70/30 Cupronickel
Aluminum bronze
0.2
Susceptible to crevice corrosion
200 Temperature (˚C)
Corrosion rate (mm/year)
82ûC
30
Naval brass
1.0
AKOT
0.5
20
1.2
Methanol containing halogen or acid Commercially pure titanium
Hg, Cd
Liquid metal
250
10
Crevice Stress corrosion Erosion corrosion cracking 1 1 2 1 1 2 2 1 3 4 4 3 2 1 3 4 4 3 2 1 2 3 2 2
Susceptible titanium materials
High temperature chloride Molten halogen salt
Ti-015Pd alloy
0
Pitting corrosion 1 1 2 4 2 4 1 2
23˚C 8m/s, sea water 150h Sand diameter < 50 m
Table 3:Environment causing titanium stress corrosion cracking
316 Stainless steel 304 Stainless steel
0.01
General corrosion 1 1 2 2 1 2 1 1
Corrosion resistance rank: 1=Excellent 2=Good 3=Ordinary 4 =Inferior
Inconel
0.05
1.4
Corrosion resistance rank
Clean Titanium Contaminated Clean Al brass Contaminated Clean 70/30 Cu-Ni Contaminated Clean Stainless steel Contaminated
10 Corrosion rate (mm/year)
Chloride concentration
Ti-015Pd alloy T-15Mo-5Zr-3Al alloy Ti-5Ta alloy AKOT Commercially pure titanium Hastelloy C Monel
Table 2:Comparison of corrosion resistance of various heat exchanger materials
Boiling point
100
Corrosion rate (mm/year)
Tantalum Zirconium Hastelloy B
0.1
CI- concentration (mass %)
1
10
Fig.10:Boundary of crevice corrosion of various titanium materials and stainless steel in chloride solution
Titanium
Titanium is normally an active metal, but exhibits extremely high
Please note that titanium is corroded by alkali of high temperature and
corrosion resistance because a passive film of titanium oxide is
high concentration. (Fig. 9)
Ni-Cr-Mo alloy C (Hastelloy C)
Platinum Graphite
+0.2
(1) General properties
Tin Copper Solder(50/50) Admiralty brass, aluminum brass Manganese bronze Silicon bronze Tin bronze(G&M) Stainless steel(410,416) German silver 90~10 Cupronickel 80~20 Cupronickel Stainless steel(430) Lead 70~30 Cupronickel Nickel, aluminum bronze Nickel -chrome alloy 600 (inconel 600) Silver solders Nickel 200 Silver Stainless steel(302,304,312,347) Nickel-copper alloy 400,K-500 Stainless steel(316,317) 20 alloy (Carpenter 20) Nickel-iron-chrome alloy 825 (Inconel 825) Ni-Cr-Mo-Cu-Si alloy B (Hastelloy B)
0
-0.2
-0.4
Fig.12:Natural potential of various metals in running seawater
-0.6
-0.8
Magnesium
Zinc Beryllium Aluminum alloy
Source:LaQue, F. L.,"The behavior of nickel-copper alloys in seawater", Journal of the American society of naval engineers, vol. 53, February 1941, #1, pp.22-64 Tokushuko, Vol.41, No.5, P38
-1.0
-1.2
-1.4
-1.6
Potential (V vs SCE)
generated and is maintained in many environments.
(3) Corrosion resistance against chloride solutions Titanium is optimal in oxidizing environments in which this passive film
Unlike stainless steel and copper alloys, titanium is not subject to pitting
is formed. (Fig. 7)
corrosion or stress corrosion cracking, nor to general corrosion. (Table 2)
The passive film of titanium provides extremely high resistance to
However, titanium is subject to crevice corrosion under high-temperature
seawater because, unlike stainless steel, it is not easily broken down even
conditions in highly concentrated solutions.
by chlorine ions.
recommended to use corrosion resistant titanium alloys such as Ti-0.15Pd
In such cases, it is
(5) Erosion resistance
(7) Reactivity to gas
The erosion resistance of commercially pure titanium is far superior to
Since titanium has a strong affinity for oxygen, hydrogen, and nitrogen
that of copper alloys. (Fig. 11)
gases, care must be taken with regard to usage conditions such as temperature and pressure.
(6) Galvanic corrosion In comparison with other practical metals, the electric potential of
Titanium exhibits corrosion resistance against moisture-containing
alloy, AKOT, etc. (Fig. 10)
titanium is high. (Fig. 12) Therefore, if titanium comes in contact with
chlorine gas, but please note that titanium reacts significantly with dry
other metals of lower potential such as copper alloys and aluminum in
chlorine gas.
Please note that high-concentration non-oxidizing acids such as hydro-
(4) Stress corrosion cracking
an electrically conductive solution, corrosion of such other metals may
chloric acid and sulfuric acids at high temperatures can corrode titanium.
Titanium is subject to stress corrosion cracking only in certain special
be accelerated. (Galvanic corrosion)
In such conditions, it is recommended to use corrosion resistant titanium
environments. (Table 3)
(2) Corrosion resistance against acid and alkali
alloys such as Ti-0.15Pd alloy, Ti-Ni-Pd-Ru-Cr alloy (AKOT), etc. (Fig. 8)
(8) Other Generally, the corrosion resistance of titanium is not affected by material
When austenitic stainless steels such as SUS304 and SUS316 come in contact with titanium under room temperatures, there is generally no
Titanium exhibit excellent corrosion resistance against oxidizing acids
problem of galvanic corrosion due to the smaller potential differences
such as nitric acid, chromic acid, etc.
between these stainless steels and titanium.
history including welding, finishing, and heat treatment.
MACHINING
CORROSION RESISTANCE Table 4:Corrosion resistance of titanium and other metals in various corrosive environments
Classification
Corrosion medium
1 Hydrochloric acid (HCl) 10 1 Inorganic acids
Sulfuric acid (H2SO4) 10 10 Nitric acid (HNO3) 65 Acetic acid (CH3COOH)
Organic acids
Formic acid (HCOOH) Oxalic acid ((COOH) 2) Lactic acid (CH3CH (OH) COOH) Caustic soda (NaOH)
Alkalis Potassium carbonate (K2CO3)
Inorganic chlorides
Inorganic salts
25
Ammonium chloride (NH4Cl)
40
Zinc chloride (ZnCI2)
20 50
Magnesium chloride (MgCl2)
42
Ferric chloride (FeCl3)
30
Sodium sulfate (Na2SO4)
20
Sodium sulfide (Na2S)
10
Sodium chlorite (NaOCl)
5 15
Sodium carbonate (Na2CO3)
30
Chlorine (Cl2) Gases
10 60 10 30 10 25 10 85 10 40 5 20
Sodium chloride (NaCl)
Methyl alcohol (CH3OH) Carbon tetrachloride (CCl4) Organic compounds Phenol (C6H5OH) Formaldehyde (HCHO)
Hydrogen sulfide (H2S)
95 100 Saturat 37 Dry Humid Dry Humid
Ammonium (NH3)
100
Seawater
-
Naphtha
-
Others
Degree of corrosion resistance
Corrosion resistance
Conc. Temperature (mass%)
(˚C) 25 Boiling 25 Boiling 25 Boiling 25 Boiling 25 Boiling 25 Boiling Boiling Boiling 25 Boiling 25 60 Boiling Boiling 100 Boiling Boiling Boiling 25 Boiling 25 Boiling Boiling Boiling 25 Boiling 25 Boiling 25 Boiling 25 Boiling 25 25 25 Boiling 25 Boiling 25 Boiling 25 25 25 25 40 100 25 100 80 180
Table 5:Difficulties in cutting and shearing titanium and countermeasures
Commercially pure titanium
Ti-0.15Pd
Unalloyed zirconium
304 stainless steel
Countermeasures
• Heat build-up accumulates easily due to less heat capacity in addition to less thermal conductivity. • Titanium itself reacts easily to cutting tools because of it's active material.
• Slower cutting speed (ex. to 1/3 or less of steel cutting speed ) and re-set the cutting feed to a fairly coarse pitch, for exothermal control. • Use a coolant as much as possible for cooling down the titanium and cutting tool (Generally a non-soluble oil coolant is used for low-speed heavy-duty cutting and shearing and a soluble cutting coolant is used for high speed cutting/shearing. • Replace a cutting tool earlier than usual. If ceramic-, TiC- and TiN-coated tools are used for cutting/shearing titanium, their lives get shorter. In general, hard steel tools are used (for cutting/shearing large quanties of titanium by machines with sufficient rigidity and high power capacity) and high-speed carbide tool are used (for cutting/shearing small quanties of titanium by machine with low power capacity.
• The cutting power fluctuates due to chips of saw-tooth form. (This is caused by cutting heat concentrating to the cutting section and local deformation of titanium.)
• Fully cool down the tool and titanium, in addition to exothermic control by the above recommended conditions. • Use a cutting/shearing machine with enough rigidity, power and an adjustable broad cutting speed range.
Titanium reacts rapidly to oxygen, because of its active metal. (Formed titanium work never burns, but cutting chips and polishing compound could ignite from welding and grinding sparks or strong impact.)
Clean the cutting and shearing machines periodically to prevent chips from being deposited. Use dry sand, common dry salt, graphite powder and metal extinguisher as fire extinguishing agents /extinguishers.
Hastelloy C
Seizure occurs, then causing a cutting tool to wear earlier.
Chattering (Vibration arising from titanium cutting/shearing is about 10 times as much as that from steel cutting/shearing.)
Chips burning No data available
0.125mm year or less 0.125 0.5mm year 0.5 1.25mm year Local corrosion such as pitting and crevice corrosion resistance
Causes
Difficulties
Table 6:Tool materials recommended for titanium machining Tool material Tungsten carbide
High-speed steel
JIS tool material codes Class-K
K01, K05, K10 , K20 , K30, K40
Class-M
M10, M20, M30 , M40
V-based
SKH10 , SKH57, SKH54
Mo-based
SKH7, SKH9, SKH52, SKH53, SKH55, SKH56
Powdered high-speed steel KHA Diamond
Man-made diamond, natural diamond
Material types used frequently
(1) Cutting
1.25mm year or more
The properties of machinability of titanium are similar to those of stainless steel, though slightly inferior. However, the application of easy-to-machine conditions enables trouble-free lathe turning, milling, drilling, threading, etc. Of course, the machinability of titanium differs according to the material quality. For example, commercially pure titanium and titanium alloys offer excellent machinability, while titanium alloy is the most inferior in machinability. - alloy is an intermediate material between the former two alloys. The main difficulties experienced with titanium cutting are shown in Table 5. The tool materials recommended for titanium cutting are shown in Table 6.
(2) Shearing
Burr often occur when shearing titanium, and therefore a key point is to slightly reduce the upper blade - lower blade clearance. 5% of plate thickness is a guideline (with stainless steel it is 10%). The shear resistance of titanium is approximately 80% of its tensile strength. It is possible to shear titanium with a shearing machine, provided that the machine is capable of shearing materials with tensile strength equal to that of titanium. Of course, titanium cutting is possible by means other than a shear machine. Please contact us for details.
FORMING Due to its potential for cold bending and press-forming, titanium is are mainly classified into
,
-
and
Material
alloys, and the formability
0
differs according to the type of titanium alloy. Warm and hot formings are used with
and
-
alloys because of their insufficient cold
formability and large spring-back. (Fig. 13) The forming methods applied are mainly press-forming methods such as bending, deep drawing, stretch forming, and spinning, the same as those used with stainless steel.
In the solution-treated condition,
alloy can be cold formed. formed
Table 7:Bending properties of commercially pure titanium sheets - 1 (4t, U-shaped bending)
Forming temperature (˚C)
generally used as a material for press-formed products. Titanium alloys
200
400
600
800
Commercially pure KS50, KS70 titanium
alloy
Ti-5Al-2.5Sn
titanium alloy, thereby achieving strength ranging from 1300
to 1500 MPa.
alloy
Ti-8Al-1Mo-1V
- alloy
Ti-6Al-4V
Material
KS40
2.5
2.0
1.0
Tight contact
OK
OK
OK
NG
OK
OK
OK
NG
KS60
OK
OK
NG
NG
KS70
OK
KS50
The key points in bending and press-forming are described below.
alloy
Bending radius (R/t)
Bending direction
Material
titanium
Aging treatment can be applied to post-
Table 8:Bending properties of commercially pure titanium sheets - 2 (0.5t, knife edge and tight-contact bending)
T-bending
NG
NG
NG
Bending direction
90degree knife edge
135degree knife edge
Tight contact
T
OK
OK
OK
L
OK
OK
OK
T
OK
OK
NG
L
OK
OK
NG
KS40
KS50
Ti-15Mo-5Zr-3Al : Medium forming
: Severe forming
Fig.13:Forming temperature ranges for commercially pure titanium and titanium alloys
Table 9:In-plane anisotropy in bending of commercially pure titanium sheets Bending properties Material Thickness (mm) T-bending L-bending
(1) Bending The spring-back of both commercially pure titanium and titanium alloys tends to be greater than that of other metals. Of the commercially pure
Bending method
KS40
4
OK
NG
135degree knife edge closely contact
kS50
4
OK
NG
135degree knife edge
KS60
3
OK
NG
90degree knife edge
KS70
4
OK
NG
R=2t, U-shaped bending
Table 10:Bending properties of Ti-15V-3Cr-3Sn-3AI alloy sheets Thickness Bending 105degree (mm) direction R=2t
90degree knife edge
135degree knife edge
Tight contact
T
OK
OK
OK
NG
L
OK
OK
OK
NG
T
OK
OK
NG
NG
L
OK
OK
OK
NG
0.5
1.0
* The datum of Tables 7 ~10 were all taken from pages 77, 78 and 81 of "Titanium Machining Technology " edited by Japan Titanium Association and issued by NIKKAN KOGYO SHIMBUN.LTD.
titanium materials, the soft materials KS40S and KS40 exhibit the same level of spring-back as SUS304, but the higher the strength of the material, the greater the spring-back. An effective method of reducing spring-back is to bend the material at a bending angle allowing for the spring-back value, or to use a die set matching the sheet thickness and pressing the material until it is in perfect contact with the die set. For commercially pure titanium, cold (room temperature) bending is possible up to KS40S to KS70. KS40S and KS40 will respond to most bending angles, although it depends on the sheet thickness. Materials of higher strength require a larger bending radius. Hot bending is effective
(2) Press-forming
in bending high-strength materials (ex. KS85m, KS100, etc.) exceeding KS70. Caution must be used with KS40 and KS50 because hot bending may deteriorate the bendability characteristics.
Press-forming is mainly applied to commercially pure titanium, and is usually performed at room temperature. The formability of
T-bending
Rolling direction
bending than for L-bending. (Fig. 14) Therefore, care must be exercised in sheet cutting. On the other hand, the sheet cutting direction does not titanium alloy because
titanium are better than its stretch forming properties.
appropriate press-forming condition and designing a forming die set.
In such
much more effective to remove buffing traces by pickling. 7
10
Commercially pure titanium
L-bending
12.1
36.2
KS40
11.2
35.4
KS50
10.3
33.7
7.5
26.3
6.9
23.1
7.9
27.6
13.0
40.5
8.8
29.7
10.1
37.2
1.0
KS70
to press-forming subjected to many stretch forming factors. In contrast, KS40 and KS50 are also suitable for press-forming subjected
KS40S
KS60
Of the commercially pure titanium metals, the softest, KS40S, is suited
important to buff perpendicularly to the bending axis. Furthermore, it is
Tables
Thus it is
important to consider deep drawing factors when selecting an
cases, the surface may be effectively smoothed by buffing, but it is
Stretch forming height (mm)
forming and achieving dimensional accuracy.
and deep drawing, but the deep drawing properties of commercially pure
In some cases, the bending properties of titanium may deteriorate
Thickness Erichsen value (mm) (mm)
Material
The main deformation conditions in press forming are stretch forming
of less anisotropy in the bending plane.
depending on the surface roughness of the bending surface.
titanium
alloy is comparable to that of commercially pure titanium KS50 KS70, but be aware that high spring-back will cause difficulty in
The bendability of commercially pure titanium is generally better for T-
generally need to be considered when cutting
Table 11:Stretch formability of commercially pure titanium, titanium alloy and steel material
Ti-15V-3Cr-3Sn-3Al
to many deep-drawing factors.
show the bending properties of commercially pure
titanium and titanium alloys.
Table 11 shows the stretch formability of various materials.
SUS304
Titanium galls easily to die sets, so lubrication is required to suit the
SUS430
press-forming conditions.
For example, lubricants such as grease and
oil, or wax-based lubricants and graphite grease are used in pressforming at room temperature. It is also effective to affix a polyethylene sheet to the blank.
Fig.14:Definition of bending direction
0.6 Mild steel
Taken from:page 84 of "Titanium Press-forming Technology" edited by Japan Titanium Association and issued by the NIKKAN KOGYO SHIMBUN.LTD. and KOBE STEEL's internal technical data
JOINING 22
Various joining techniques such as welding, brazing, pressure-welding, diffusion bonding, and mechanical joining (e.g. bolting, etc.) may be used to join titanium plates. (Fig. 15)
Table 13:Representative brazing materials and brazing temperatures
20
Brazing material
Heated & quenched
18 16
Arc welding Electron beam welding
Welding methods
Laser welding Spot welding Seam welding Flash butt welding
Resistance welding Available joining methods
Corrosion rate (mm/year)
1% H2SO4
TIG welding(GTAW) MIG welding(GMAW) Plasma welding
12
Annealed material
Pressure welding
Other methods
Diffusion bonding
6
Portion welded under perfectly shielded argon gas atmosphere 65% HNO3 Annealed and heated & quenched
0
0
0.1
0.2
0.5
Shield gas
375
145
419
155
Commercially pure titanium (JIS Class-3)
20
530
185
562
218
Ti-0.15Pd (JIS Class-12)
5
401
153
405
178
After-shield
Filler
Stainless wool Shield gas
Titanium plate Back shield Tungsten electrode
Welding method: TIG welding Electrode: same material as base metal ( 2mm)
830
Ag-20Cu-2Ni-0.2Li
920
Ag-20Cu-2Ni-0.4Li
920
Ag-9Ga-9Pd
900
Ag-27Cu-5Ti
840
Ti-15Cu-15Ni
930
Ti-20Zr-20Cu-20Ni
890
Ti-25Zr-50Cu
890
Shield gas
Strain relief annealing is applied to commercially pure titanium and titanium alloys after hot and cold working. Annealing is also applied to recover or re-crystallize the deformed microstructure. Thus, annealing is effective for stabilizing the microstructure and dimensions of the treated product, and to improve the cutting properties and mechanical properties. Heat treatments such as solution treatment & aging (STA), and double solution treatment & aging (STSTA) are applied to titanium alloys to improve strength, toughness, and fatigue properties. Titanium alloys of more phase exhibit better heat-treatment properties. With titanium alloy, after solution treatment it is possible to achieve tensile strength of around 1600 MPa by a two-stepped aging process of low-temperature aging and high-temperature aging.
An electric furnace with a fan agitation function is preferable for temperature control in the heat-treatment of titanium (Fig. 19). Furthermore, when using an annealing furnace, in order to prevent hydrogen absorption, it is necessary to increase the air ratio and make the furnace atmosphere one of weak oxidation, and to contain the product to be treated in a muffle to protect the product from direct contact with flame. Table 14 shows typical conditions for the heat treatment of titanium materials.
Fig.17:TIG welding torch and shield jig for titanium plate
Table 14:Representative heat treatment conditions for titanium materials
(1) Welding Titanium has excellent properties of weldability, and there is little change in the mechanical properties or corrosion resistance of the welded area. (Table 12, Fig. 16) However, at high temperatures titanium has a high affinity for oxygen gas and nitrogen gas, and reaction with these gases may result in hardening and embrittlement which could cause a decline in ductility and the occurrence of blowholes in the welded area. Hence, welding to titanium must be performed in an inert gas or vacuum. In addition, the welding material and electrode, and the welding environment must be cleaned thoroughly before welding. Of all titanium materials, commercially pure titanium and alloy have the best properties of weldability.
Ag-28Cu-0.2Li
HEAT TREATMENT
Table 12:Mechanical properties of titanium thick plate to plate welded joint
9
920
Fig.16:Effects of welding on corrosion rate of commercially pure titanium
TIG torch
Commercially pure titanium (JIS Class-2)
Portion welded under imperfectly shielded argon gas atmosphere
Fig.18:Appearance of TIG-welded portion of titanium
0.3 0.4 Iron content (%) : Annealed : Heat & quenched (simulation of welded portion)
Fig.15:Titanium jointing methods
Material
Ag-7.5Cu-0.2Li
8
Mechanical joining (bolting, etc.)
Base metal Weld Hv Hv Thickness Tensile Tensile (mm) strength hardness strength hardness (10kg) (10kg) (MPa) (MPa)
800
10
2 Explosive welding Rolling pressure welding Friction welding
Ag-3Li
14
4
Brazing
titanium
Of the welding methods shown in Fig. 15, TIG welding is the generally used. As shown in Fig. 17, a welding torch with a gas shield jig is used for TIG welding. A Reaction of the welded portion to oxygen, etc. is prevented by putting it under an argon gas atmosphere.
Brazing temperature (˚C)
If the welded portion reacts to gas, the result is discoloration as shown in Fig. 18. This phenomenon allows us to determine the weld quality, to some extent, by an inspection of its appearance. The welding of titanium to steel materials had previously been considered difficult, but the technology developed by KOBE STEEL for welding heterogeneous metals has enabled techniques such as the direct lining of titanium to steel plate. (Please refer to "Steel Pipe Piles for Wharf" on page 6.)
(2) Brazing Brazing is applied when titanium cannot be welded to other metals or when welding is difficult due to complex structures. Brazing to titanium is performed under a vacuum or inert gas atmosphere. The use of the brazing materials listed in Table 13 is recommended.
Available heat treatment methods Material Commercially pure titanium
titanium alloy
Ti-3Al-2.5V
Stress relief
Solution treatment
Aging
480-595˚C 650-815˚C 15-240min 15-120min
-
-
370-595˚C 650-790˚C 15-240min 30-120min
-
-
Annealing
480-650˚C 60-240min
705-870˚C 15-60min
900-970˚C 2-90min
480-690˚C 2-8hr
790-895˚C titanium Ti-15V-3Cr 30-60min alloy -3Sn-3Al
760-815˚C 3-30min
760-815˚C 2-30min
480-675˚C 2-24hr
Ti-6Al-4V
Taken from: AMS-H-81200 Product shapes: thin plates, thick plates
Fig.19:Furnace for titanium products
SURFACE TREATMENT 1400
min
˚C
700˚C
10
30
60
Ammeter
120
A
Ti-6Al-4V
V 400
DC power
Solid lubricated Ti-6AI-4V Voltmeter
600˚C
1000
-7
Oxide film thickness (Å=10 mm)
1200
Gas-nitrided Ti-6AI-4V
450
800
Electrolytic vessel
Non-lubricated
600
SUJ2 Friction distance : 500m
WC sprayed Ti-6AI-4V
500
Speed : 83.3mm/sec Load : 980N
400
KENI COAT Ti-6Al-4V
550
500˚C
0
100
150
Anode (Ti)
Fig.25:Schematic diagram of anodizing method
200
Wear (mg)
200
400˚C Fig.24:Sliding wear test results of Ti-6AI-4V alloys to which various surface treatments were applied
600
0 0
50
Electrolyte Cathode (AI)
20
40
60
80
100
120
Atmospheric oxidizing time (minutes)
650
Fig.20:Relationship between atmospheric oxidizing time and oxide film thickness
700
300
2000
Conforming to the atmospheric oxidizing treatment conditions in Fig.20 Atmospheric oxidizing treatment
-7
Oxide film thickness (Å=10 mm)
Fig.21:Appearance of commercially pure titanium specimens after atmospheric oxidation 70˚C
200 Temperature (˚C)
Susceptible to corrosion Corrosion reduction (mg/cm2)
2.0
100 Polishing
Immune to corrosion
Anodizing
0
PdO-TiO2 coated titanium Commercially pure titanium
4
Green yellow Green
1000
Purple Yellow
Blue 1.0
0
6
Brown Gold treatment
0
50
100
150
Voltage for anode oxidizing (V)
HCI (mass %)
Fig.22:Boundary of active area to passive area of surface treated titanium materials in hydrochloric acid solution
1500
500
Ti-0.15Pd
2
Pink
0 0
Fig.26:Relationship of anode oxidizing treatment voltage vs titanium oxide film thickness 2
4
6
8
10
Fig.27:Appearance of anodized titanium (The numerals show the applied anodizing voltages)
HCI (mass %)
Fig.23:Corrosion resistance of PdO-TiO2 coated titanium, commercially pure titanium and Ti-0.15Pd alloy in hydrochloric acid
(1) Surface treatment for corrosion resistance ¥ Atmospheric oxidizing treatment The excellent corrosion resistance of titanium is due to a thin film of titanium oxide on the surface that is no more than a few dozen angstrom in thickness. Hence, the corrosion resistance can be further improved by investing the titanium with additional oxide film through atmospheric oxidizing treatment of its surface. (Fig. 20 22) Furthermore, atmospheric oxidizing treatment greatly inhibits hydrogen absorption.
¥ Noble metal coating The general corrosion resistance and crevice corrosion resistance of titanium can be further improved by coating the surface with a film incorporating PdO-TiO2. (Fig. 23)
(2) Surface treatment for wear resistance
(3) Surface treatment for surface design
¥ KENI COAT "KENI COAT" is a hard electric Ni-P plating technology for improving wear resistance, which is one weak point of titanium. The hardness (Hv450-900), toughness, lubricity, and adhesion properties of titanium are balanced to an outstanding level, so that the treated titanium exhibits excellent wear resistance. (Fig. 24) Treated titanium is a champagne-gold color, and can also be blackened.
By forming an oxide film on the titanium surface using the anodizing, light interference allows us to achieve beautiful color tones of high saturation, according to the film thickness. (Figs. 25 27)
(4) Surface finishing Various surface finishes are available including mirror, Scotch-Brite, hairline, vibration, blast, dull, and embossed.
