JPH0815667B2 - Welding method of titanium alloy - Google Patents

Description

Detailed Description of the Invention [Object of the invention]

(Field of Industrial Application) The present invention relates to a welding method of titanium alloys used for joining titanium alloys containing a large amount of β-stabilizing element V in particular. (Prior art) When a solid solution of μ stabilizing elements such as V and Mo is dissolved in titanium, β →
The transformation point of α is lowered, and the β phase can be left relatively easily at room temperature. Generally, this β phase is a pure stable phase, and when it is subjected to aging treatment, phase decomposition occurs, and α phase is precipitated and hardened. There are various β-type titanium alloys of this kind, but among them, they contain a large amount of V, which is a β-stabilizing element.
% V-3% Al-3% Cr-3% Sn-based titanium alloys have a large specific strength and are excellent in cold workability and heat treatment. An attempt to proactively adopt a certain Al as a material for rockets and aircrafts, replacing the conventional 6% Al-4% V titanium alloy containing a large amount of Al in α-Ti up to the solid solution limit at room temperature. Is becoming more commonplace. When it is used as a material for rockets and aircraft, in addition to mechanical joining using bolts and tacks, a welding method that is metallurgical joining is often adopted. There was a method using a high energy density heat source such as electron beam welding, plasma arc welding or TIG welding. (Problems to be solved by the invention) However, the above-mentioned 15% V-3% Al-3% Cr-3
A welding method using a high energy density heat source was adopted when joining% Sn-based β-type titanium alloys, and when the aging treatment conditions during aging treatment after welding were set to correspond to the base metal portion, tends to those fracture toughness (K _I c) is poor, sometimes K _I c value of the welded parts compared to K _I c value of the base material portion becomes considerably low, poor utility as joint There was a problem that sometimes. (Object of the Invention) The present invention has been made to solve the above-mentioned conventional problems, and is ductility and fracture toughness of a titanium alloy containing 15% V-3% Al-3% Cr-3% Sn as a main component. In order to improve the reliability of the welded part of this type of titanium alloy, pay attention to the fact that (K _I c) greatly depends on the strength and the grain size, and particularly when the grain size is coarse, various changes occur. In consideration of the fact that measures such as suppressing coarsening of crystal grains in the welded portion, giving a stepwise height distribution in which the strength of the welded portion is lower than the strength of the base metal portion, are considered, In particular, it is possible to obtain a titanium alloy welded joint in which the strength of the base metal portion is maintained at a high level and the toughness of the welded portion is improved by making the structure of the welded portion appropriate. Eye to provide It is set to.

Configuration of the Invention

(Means for Solving the Problems) The method for welding a titanium alloy according to the present invention is
V: 14.0 to 16.0%, Al: 2.5 to 3.5%, Cr: 2.5 to 3.5%, Sn:
Contains 2.5 to 3.5% as an essential component, and optionally O: 0.18% or less, Fe: 0.25% or less, and optionally N: 0.03% or less, H: 0.015% or less, C: When joining titanium alloys that are regulated to 0.03% or less, similarly regulate the upper limit of each impurity component other than the above to 0.10%, and regulate the total amount of all impurities to 0.30% or less, if necessary. %, Al: 5.50-6.75%, V: 3.5-4.5% are contained as essential components, O: 0.18% or less, Fe:
It also contains 0.30% or less, and if necessary, N: 0.03% or less, H: 0.015% or less, C: 0.05 or less, Y: 0.005% or less, and if necessary, each of the impurity components other than the above The upper limit of 0.10% or less and the total amount of all impurities
In order to solve the conventional problems described above, the titanium alloy welding material regulated to 0.40% or less is used for fusion bonding with a high energy density heat source. Is used as a means. Titanium alloy to which the present invention is applied, as described above, V: 14.0 to 16.0%, Al: 2.5 to 3.5%, Cr: 2.5 to 3.5%,
Sn: 2.5 to 3.5% is contained as an essential component.
In this case, V acts on the titanium as a β-stabilizing element, and the β-structure of the titanium alloy remains stable at room temperature.
It is an element effective in obtaining a titanium alloy with excellent workability, and in order to obtain such effects sufficiently,
It is preferably in the range of 14.0 to 16.0%. Although Al acts as an α-stabilizing element on titanium, it is an element that contributes to an increase in strength and an improvement in creep characteristics in a β-type titanium alloy, and in order to sufficiently obtain such an effect, It is preferably in the range of 2.5 to 3.5%. Further, Cr acts on the titanium as a β-stabilizing element, is an element effective in improving the strength and toughness of the titanium alloy, and 2.5 to 3.5 is sufficient to sufficiently obtain such an effect.
It is preferably in the range of%. Furthermore, Sn has a neutral effect on α-stabilization and β-stabilization of titanium, is an element effective for improving the heat resistance of titanium alloys, and in order to sufficiently obtain such an effect. Is 2.5 to 3.5
It is preferably in the range of%. Further, O acts as an α-stabilizing element for titanium, but in a β-type titanium alloy, it contributes to the improvement of its strength. Therefore, it may be contained in an appropriate amount for controlling strength. %, The toughness decreases, which is not preferable, and since Fe also contributes to the improvement of the strength, it may be contained in an appropriate amount for strength control, but if it exceeds 0.25%, the toughness decreases. It is not preferable because it will bring about. Further, in the case of impurity elements, if the amount of N is large, the toughness of the base material part is lowered, so it is desirable to suppress it to 0.03% or less, and even if the amount of H is large, the toughness of the base material part is lowered, so 0.015% or less It is desirable to suppress it to 0.03% or less, since it will lower the toughness of the base material part even when the C content is large. Furthermore, in order to obtain good mechanical properties without deteriorating the toughness of the base material in the case of impurity components other than the above, it is desirable to suppress the content of each element to 0.10% or less. 0 in total amount.
It is desirable to keep it below 30%. In joining β-type titanium alloys having such a component composition, according to the present invention, as described above, an α + β-type alloy containing Al: 5.50 to 6.75% and V: 3.5 to 4.5% as essential components is used. Titanium alloy welding material is used.
In this case, Al acts as an α-stabilizing element on titanium, but is an element effective for improving the strength and toughness of the welded portion by welding using this titanium alloy welding material. Then, in order to sufficiently obtain such effects, it is preferable that the amount of Al in the titanium alloy welding material is in the range of 5.50 to 6.75%. Further, V acts on β as a β-stabilizing element and improves the toughness of the welded portion, but in order to sufficiently obtain such an effect, it is 3.5 to 4.5.
It is preferably in the range of%. Further, O acts as an α-stabilizing element on titanium, but if contained in a welded portion in an appropriate amount, it has the effect of improving strength, so it may be contained in an appropriate amount if necessary.
If it exceeds 0.18%, the toughness of the welded portion will be reduced, which is not preferable, and more preferably 0.08% or less,
Since Fe also contributes to the improvement of the strength of the welded portion, it may be contained in an appropriate amount if necessary, but if it exceeds 0.30%, the toughness of the welded portion is lowered, which is not preferable, and more preferably 0.15% or less. Is good. Furthermore, in the case of impurity elements, if the content of N is large, the toughness of the welded portion will be reduced, so 0.03% or less, more preferably 0.012
% Or less, since the toughness of the welded portion decreases even when H is large, it is desirable to suppress it to 0.015% or less, more preferably 0.005% or less. Since toughness decreases, 0.05% or less,
More desirably, it is desirable to suppress it to 0.03% or less,
Even if the amount of Y is large, the toughness of the welded part decreases, so 0.005
% Or less is desirable. Furthermore, in order to obtain good mechanical properties without deteriorating the toughness of the welded portion even with impurity components other than those described above, each is 0.10% or less, more preferably
It is desirable to suppress it to 0.03% or less, and for the same reason, it is desirable to suppress it to 0.40% or less, and more desirably 0.10% or less in the total amount of impurity elements. Then, when joining the titanium alloys having the above-described component composition using the titanium alloy welding material having the above-mentioned component composition, the high-energy-density heat source is used to perform the melt-bonding. The strength of the base material may be increased in advance by subjecting the material to an aging treatment. Then, fusion bonding is performed on the titanium alloy base material using a high energy density heat source. In this case, specifically,
TIG (Tungsten Inert Gas) welding method, electron beam welding (E
BW) method, laser beam welding (LBW) method, etc. can be adopted. In the case of TIG welding method, a welding rod or filler wire made of titanium alloy welding material having the above-mentioned composition is used. In the case of the beam welding method or the laser beam welding method, it is possible to use the insert material made of the titanium alloy welding material having the above-mentioned composition, but it is not particularly limited. (Operation of the Invention) In the titanium alloy welding method according to the present invention, the weight% is
, V: 14.0 to 16.0%, Al: 2.5 to 3.5%, Cr: 2.5 to 3.5%,
When joining titanium alloys containing Sn: 2.5 to 3.5% as an essential component, in weight%, Al: 5.50 to 6.75%, V:
Since a titanium alloy welding material containing 3.5 to 4.5% as an essential component is used for fusion bonding with a high energy density heat source, the structure of the molten portion becomes an acicular α structure,
The strength of the base metal portion is high and the toughness of the welded portion is improved. (Example) In this example, β-type titanium alloys 1 and 2 having a composition shown in Table 1 and having a plate thickness of 10 mm were used by using α + β-type titanium alloy welding material 3 different from the titanium alloys 1 and 2. Shown when welded. That is, at the time of welding, after subjecting titanium alloys 1 and 2 having the compositions shown in Table 1 below to solution treatment at 1073 ° K for 1.8ks, the titanium alloys 1 and 2 are joined to each of the joints 1a, 2a
And the groove portions 4 and 4 are formed between them. Then, using the α + β type titanium alloy welding material 3 having the composition shown in Table 2, the TIG welding torch 5 is welded under the welding conditions shown in Table 3. TIG welding is performed, and a titanium alloy welding material 3 different from the base metal is welded to the groove portions 4 and 4 to form welded welded portions 6 and 6, followed by aging at 763 ° K. Treated. Then, such overlay welding of different materials of titanium alloys 1 and 2 is performed three times, and fracture toughness test pieces (ASTM E399 CT TYPE) are collected from the weld overlays 6 and 6 and welded. The fracture toughness (K _I c) of the joint was measured. Table 4 shows the results. (Comparative Example) In this comparative example, β-type titanium alloys 1 and 2 each having the composition shown in Table 1 and having a thickness of 10 mm and having the same composition as those in the above-described examples were used as the β-type titanium alloy welding material of the same kind as the titanium alloys 1 and 2. The case of welding using (3) is shown. That is, at the time of welding, titanium alloys 1 and 2 having the compositions shown in Table 1 below are subjected to a solution treatment at 1073 ° K for 1.8ks, and then the titanium alloys 1 and 2 are joined to each other at the joints 1a. , 2a
To form the groove portions 4, 4 between them, and then using a β-type titanium alloy welding material (3) having the same composition as the chemical composition of the welding base metal shown in Table 1, Three
TIG welding is performed under the welding conditions shown in the table by the TIG welding torch 5, and the titanium alloy welding material (3) of the same kind as the base metal is welded to the groove portions 4 and 4 by welding, and the weld overlay portion (6, 6) was formed, followed by aging treatment at 763 ° K. Then, such overlay welding of titanium alloys 1 and 2 with the same kind of material is performed twice, and fracture toughness test pieces (ASTM E399 CT TYPE) are sampled from each overlay welding part (6, 6) and welded. The fracture toughness (K _I c) of the joint was measured. The results are shown in Table 4. As is clear from the results shown in Table 4, in Examples Nos. 1 to 5 in which overlay welding was performed using the base material titanium alloys 1 and 2 and the different titanium alloy welding material 3, fracture toughness (K _I c)
There has become approximately 170Kgf · mm ^-3/2 longitudinal or more, the base material of titanium alloy 1 and the same type of titanium alloy welding material (3) Comparative Example No.1 was performed overlay welding using, It was confirmed that a welded joint part was obtained that showed considerably superior toughness compared to the case of 2.

【The invention's effect】

The welding method of the titanium alloy according to the present invention, in% by weight,
V: 14.0 to 16.0%, Al: 2.5 to 3.5%, Cr: 2.5 to 3.5%, Sn:
When joining titanium alloys containing 2.5 to 3.5% as an essential component, in weight%, Al: 5.50 to 6.75%, V: 3.5 to
By using a titanium alloy welding material containing 4.5% as an essential component to perform fusion bonding with a high energy density heat source, the structure of the fusion part is suitable and the strength of the base material part is high. It is possible to obtain a titanium alloy welded joint with improved toughness at the welded part while maintaining it, and it has excellent specific strength, corrosion resistance and cold workability.
This has a remarkably excellent effect that the application range of the 15% V-3% Al-3% Cr-3% Sn-based β-type titanium alloy can be further expanded.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an implementation point of a titanium alloy welding method according to the present invention. 1,2 ... Titanium alloy, 3 ... Titanium alloy welding material, 5 ... High energy density heat source.

Claims (1)

[Claims] 1. By weight%, V: 14.0 to 16.0%, Al: 2.5 to 3.5
%, Cr: 2.5-3.5%, Sn: 2.5-3.5% when joining titanium alloys containing as essential components, in% by weight, A
A method for welding a titanium alloy, characterized in that a titanium alloy welding material containing l: 5.50 to 6.75% and V: 3.5 to 4.5% as essential components is welded and joined by a high energy density heat source.