JPH0635065B2 - Titanium alloy joining method - Google Patents

Description

Detailed Description of the Invention

(Industrial field of application) The present invention relates to a method for joining titanium alloys used for joining titanium alloys containing a large amount of β-stabilizing element V in particular. (Prior Art) When a β-stabilizing element such as V or Mo is solid-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 metastable phase, and when it is subjected to an aging treatment, it undergoes phase decomposition, and the α phase is precipitated and hardened. There are various β-type titanium alloys of this type,
Above all, containing a large amount of V, which is a β-stabilizing element, 15%
V-3% A-3% Cr-3% Sn-based titanium alloy is
Since it is an alloy that has a large specific strength and is excellent in cold workability and heat treatment property, in recent years, a large amount of α-stabilizing element A has been added to α-Ti up to the solid solution limit at room temperature. In place of the conventional 6% A-4% V titanium alloy, attempts have been made to positively adopt it as a material for rockets and aircraft. 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 has been 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% A-3% Cr
When a welding method using a high energy density heat source is adopted when joining -3% Sn-based β-type titanium alloys to each other, and when the aging treatment conditions during the aging treatment after welding are set to correspond to the base metal part, since becomes curing rate of the welded parts is large, it tends to what fracture toughness of the welded parts (K _IC) is poor, that K _IC value of the welded parts in comparison with the K _IC values of the base material portion rather low However, there is a problem that the practicality as a joint may be poor. (Object of the Invention) The present invention has been made to solve the above-described conventional problems, and is ductility and fracture toughness of a titanium alloy containing 15% V-3% A-3% Cr-3% Sn as a main component. (K _IC )
Is strongly dependent on strength and crystal grain size, and particularly paying attention to the fact that when the crystal grain size is coarse, remarkable embrittlement occurs, and in order to improve the reliability of the welded part of this kind of titanium alloy, the welded part In consideration of possible measures such as suppressing the coarsening of the crystal grains of the steel, and giving a stepwise hardness distribution in which the strength of the welded part is lower than the strength of the base metal part, the latter stepped shape in particular is considered. It is an object of the present invention to provide a joining method for a titanium alloy, by which it is possible to obtain a joined joint in which the toughness of the welded portion is improved without lowering the strength of the base metal portion by giving the hardness distribution.

[Constitution of the invention]

(Means for Solving the Problems) The titanium alloy joining method according to the present invention is
V: 14.0 to 16.0%, A: 2.5 to 3.5%,
Cr: 2.5 to 3.5%, Sn: 2.5 to 3.5% as a basic component, and optionally O: 0.18
% Or less, Fe: 0.25% or less, and if necessary, N: 0.03% or less, H: 0.015% or less,
C: 0.03% or less is regulated, and similarly, if necessary, the upper limit of each impurity component other than the above is regulated to 0.10%,
When joining titanium alloys in which the total amount of all impurities is restricted to 0.30% or less, after pre-aging treatment is performed on the titanium alloys, the titanium alloys are brought into contact with each other, and a high energy density heat source is applied to the contact portions. After applying and melt-bonding, at least the welded portion or both the base material portion and the welded portion is subjected to the second aging treatment, the strength of the base material portion is secured by the preliminary aging treatment, and the toughness of the welded portion is It is characterized in that it is ensured by the second aging treatment after welding, and such a construction of the joining method of the titanium alloy is a means for solving the above-mentioned conventional problems. The titanium alloy to which the present invention is applied, as described above,
V: 14.0 to 16.0%, A: 2.5 to 3.5%,
Cr: 2.5 to 3.5% and Sn: 2.5 to 3.5% are contained as basic components. In this case, V is an element effective for acting as a β-stabilizing element on titanium so that the β-structure of the titanium alloy remains stable at room temperature and a titanium alloy excellent in workability is obtained. But,
If it is less than 14.0%, such an effect cannot be sufficiently obtained, and if it exceeds 16.0%, the precipitation rate of the α phase is lowered, which causes densification and strength reduction, which is not preferable. . A acts as an α-stabilizing element on titanium, but in the β-type titanium alloy, A is an element that contributes to the increase of strength and the improvement of creep characteristics, and in order to sufficiently obtain such an effect, 2.5-
It is preferably in the range of 3.5%. Further, Cr acts on β as a β-stabilizing element, is an element effective for improving the strength and toughness of the titanium alloy, and 2.5 to 3.5 is necessary for sufficiently obtaining such an effect. It is preferably in the range of%. Furthermore, Sn is α of titanium
It is an element that has a neutral effect on stabilization and β stabilization and is effective for improving the heat resistance of titanium alloys, and 2.5 to 3.5 is required to sufficiently obtain such effects.
It is preferably in the range of%. Further, O acts as an α-stabilizing element on titanium, but in a β-type titanium alloy, it contributes to the improvement of its strength, so it may be contained in an appropriate amount as necessary for strength control. If it exceeds 18%, toughness is deteriorated, which is not preferable, and since Fe also contributes to the improvement of strength, it may be contained in an appropriate amount as necessary for strength control, but if it exceeds 0.25%, toughness is increased. It is not preferable because it results in a decrease in Further, in the impurity element, if the amount of N is large, the toughness of the base material portion is lowered, so it is desirable to suppress the content to 0.03% or less, and even if the amount of H is large, the toughness of the base material portion is lowered. It is desirable to suppress the content to 0.015% or less, and it is desirable to suppress the content to 0.03% or less because the toughness of the base material portion is reduced even when the C content is large. Furthermore, in order to obtain good mechanical properties without deteriorating the toughness of the base material, it is desirable that the content of impurities other than the above is suppressed to 0.10% or less. It is desirable to suppress the total amount of elements to 0.30% or less. Then, when joining titanium alloys having such components, first, a preliminary aging treatment is performed as the first aging treatment for the titanium alloys. This preliminary aging treatment is carried out in order to secure the strength of the base material portion, and is preferably carried out, for example, in the range of 700 to 800 ° K. That is, if the temperature of the pre-aging treatment is too low, the time required for the pre-aging treatment becomes too long, which is not practical. On the contrary, if the temperature of the pre-aging treatment is too high, the strength of the base material portion is lowered, which is not preferable. . Then, each titanium alloy is subjected to the above-mentioned pre-aging treatment, brought into contact with each other at the joint portions, and a high energy density heat source is applied to the contact portions to perform the fusion joining. In welding using this high energy density heat source, electron beam welding (EBW) method, laser beam welding (LBW)
Law, TIG (Tungsten Inert Gas)
A welding method or the like can be adopted. After welding, at least the welded portion or both the base metal portion and the welded portion is subjected to the second aging treatment. This aging treatment is performed to secure the toughness of the welded portion, and in this case, the temperature Tc of the aging treatment applied to at least the welded portion is higher than the temperature Tp of the first preliminary aging treatment applied to the titanium alloy ( Tc> Tp) is particularly desirable, for example, 700
It is desirable to set it in the range of up to 900 ° K. That is,
If the temperature of the second aging treatment is too low, the effect of improving the toughness of the welded portion decreases, and conversely, if the temperature of the aging treatment is too high, the strength of the base material portion decreases, which is not preferable. The second treatment in consideration of the improvement in the toughness of the welded portion is not necessarily limited to the aging treatment performed only once. (Operation of the Invention) In the titanium alloy joining method according to the present invention, when joining β-type titanium alloys having the above-described specific components, the titanium alloys are subjected to the first preliminary aging treatment and then each After making contact with each other at the joint portion and applying a high energy density heat source to the contact portion to perform melt-bonding, at least the welded portion or both the base material portion and the welded portion is subjected to the second aging treatment. In the second pre-aging treatment, the pre-aging treatment conditions were set taking into consideration the strength improvement of the base metal part in particular, and in the second aging treatment after welding, the aging treatment condition was taken into consideration especially in consideration of the toughness improvement of the welded portion. By setting so that the strength of the base metal part is improved after the preliminary aging treatment, the welded part after welding is subjected to the second aging treatment performed thereafter. What becomes excellent in toughness, joint portions of the titanium alloy toughness of the welded parts without reducing the strength of the base material portion serves as a good is formed. (Example) In this example, titanium alloys having a composition shown in Table 1 and having a plate thickness of 10 mm were joined together. At the time of joining, first, a titanium alloy having the components shown in Table 1 was subjected to a solution treatment at 1073 ° K for 1.8 Ks, and a part thereof was subjected to the solution treatment according to the present invention and then subjected to a solution treatment at 573 ° K, 673. Pre-aging treatments at ° K and 753 ° K were performed. Next, the solution-treated titanium alloys are butted and brought into contact with each other at the joints, and the titanium alloys that have been pre-aged at each temperature are butted and brought into contact with each other at the joints. TIG welding was performed at each contact portion under the conditions shown in Table 2, and electron beam welding was performed at each contact portion for the other part under the conditions shown in Table 3. Next, after performing TIG welding and electron beam welding under the conditions shown in Tables 2 and 3, 773 ° K and 8
The second aging treatment was performed at 23 ° K. Then, changes in hardness distribution due to aging and mechanical properties, that is, strength, ductility, and fracture toughness (K _IC ) were obtained from the center of the molten portion along the base material portion. Of these, the hardness distribution due to aging was measured with a micro Vickers (load of 500 g), and regarding mechanical properties, tensile test pieces (ASTM E8 φ6.25 mm) and fracture toughness test pieces (ASTM E399 CT TYPE) were prepared. It was measured. In this case, the pulling direction was orthogonal to the welding line and the base metal portion was the rolling direction. FIG. 1 shows a solution heat-treated material subjected to solution heat treatment at 1073 ° K × 1.8 ks, and 753 ° K × 5 after the solution heat treatment.
The preliminary aging-treated material subjected to the preliminary aging treatment for 7.6 ks shows the result of examining the hardness distribution as it is after the electron beam welding under the welding condition L. As shown in FIG. 1, there is no change in hardness and a substantially flat distribution in the as-welded state of the solution treated material (marked with ◯ in FIG. 1). On the other hand, in the pre-aged material at 753 ° K, the base material part has a Vickers hardness Hv of about 420 due to the pre-aging treatment, and the strength of the base material part is high, It is clear that a region softened by re-solutionization is generated from the melted portion to the heat affected zone. Fig. 2 shows the joining alloys (○ and ● in Fig. 2) that were not subjected to pre-aging treatment and were subjected to electron beam welding under the condition L in Table 3 for the solution heat treated material, and 753 ° K for the solution heat treated material. After pre-aging treatment, electron beam welding was performed under the condition L in Table 3 and the joining alloy with pre-aging treatment (□, ■ in Fig. 2).
The results of examining the hardness distribution after the second aging treatment at 823 ° K for 7.2 ks and at 823 ° K for 36 ks. As shown in FIG. 2, it is clear that the hardening is the fastest at about 7 to 12 mm from the melting center portion corresponding to the heat affected zone, and then the melting portion and the base metal portion are in this order.
In the 36 ks aging treatment in which the hardness is almost saturated by the aging treatment, when the preliminary aging treatment is not performed (Fig. 2, ●
(Mark) has a relatively flat hardness distribution, but when pre-aged at 753 ° K according to the present invention (second
In the mark (■) in the figure, the hardness of the pre-aged base metal part is slightly reduced, but the welded part has a lower hardness distribution than the base metal part, and It is clear that it has been realized. Next, the result of measuring the hardness distribution after the second aging treatment at 773 ° K after welding is illustrated in FIG. As shown in FIG. 3, the fact that the hardening of the heat-affected zone is fast and that the hardening is almost saturated at 36 ks after the start of the aging treatment is almost the same as that shown in FIG. The distribution is almost flat, unlike the case of FIG. FIG. 4 shows that the titanium alloy subjected to the solution heat treatment at 1073 ° K for 1.8 ks and then the pre-aging treatment at 753 ° K for 57.6 ks under the conditions N and L shown in Table 3. The results of examining the strength and toughness of the base material portion and the welded portion when the temperature of the second aging treatment is used as a variable are shown after the electron beam welding is performed. in this case,
The second aging treatment time is set to 36 ks at which the curing is saturated. As is clear from FIG. 4, in the aging treatment at 773 ° K, the strength difference between the welded portion (marked with ◯ and ● in FIG. 4) and the base metal (marked with □ in FIG. 4) is small. Also, the fracture toughness (K _IC ) is low. On the other hand, in the aging treatment at 823 ° K, the decrease in the base metal strength due to the increase in the aging temperature is smaller than that in the welded portion, and the strength difference between the base metal portion and the welded portion is about 170M.
Pa. Further, _{K IC} of the welded parts is almost close to _{K IC} of Hahazai portion (about 50~70MPa ^{· m 1/2).} The strength of the base metal part and the strength of the welded part decrease as the aging temperature rises, whereas the fracture toughness of the welded part shows the opposite tendency to the strength, especially at around 800 ° K. At the boundary, the fracture toughness value rises sharply as the aging temperature rises. Therefore, in order to improve the strength of the base metal part and the toughness of the welded part at the same time, rather than going through the steps of solution treatment → welding → aging treatment, solution treatment → pre-aging treatment ->Welding-> It is more desirable to set each aging condition so as to go through the process of aging treatment. Therefore, according to the present invention, the toughness of the welded portion was improved without impairing the strength of the base metal portion. It was confirmed that it is possible to obtain a welded joint of titanium alloy. In addition, when the titanium alloy which has been subjected to the pre-aging treatment after the solution treatment is welded under the TIG welding conditions shown in Table 2 and the second aging treatment is performed after the welding,
The same excellent results as in the case of welding by the electron beam welding described above were obtained. In the first preliminary aging treatment, the preliminary aging treatment conditions were set in consideration of the strength improvement of the base metal part in particular, and after the TIG welding. In the second aging treatment of, the aging treatment condition is set in consideration of the improvement of the toughness of the welded portion, so that the toughness of the welded portion is good without lowering the strength of the base metal portion. A titanium alloy welded joint could be obtained. Furthermore, the temperature of the pre-aging treatment is 573 ° K and 673 ° K.
In case of, the aging treatment after welding is 773 ° K, 82
It did not show a particularly remarkable effect on the high temperature age hardening at 3 ° K.

【The invention's effect】

In the titanium alloy joining method according to the present invention, the weight percentage is
V: 14.0% to 16.0%, A: 2.5 to 3.5
%, Cr: 2.5 to 3.5%, Sn: 2.5 to 3.5%
At the time of joining titanium alloys containing as a basic component, the titanium alloys are pre-aged and then contacted at each joint, and a high energy density heat source is applied to the contact portion, and at least welding is performed. Since the part is subjected to aging treatment, the strength of the base metal part is secured by the preliminary aging treatment prior to welding, and the toughness of the welded part is secured by the aging treatment after welding. Since it is possible to obtain a bonded joint in which the toughness of the welded part is improved without lowering the strength, it is possible to obtain excellent strength, corrosion resistance and cold workability.
This has a remarkably excellent effect that the range of application of the β-type titanium alloy of% V-3% A-3% Cr-3% Sn can be further expanded.

[Brief description of drawings]

FIG. 1 shows a solution heat-treated material subjected to solution heat treatment at 1073 ° K × 1.8 ks, and 753 ° K × 5 after the solution heat treatment.
A graph exemplifying the result of examining the hardness distribution of the as-welded steel after welding for the pre-aged material subjected to the pre-aging treatment of 7.6 ks, and FIG. 2 is a joining alloy without the pre-aging treatment, For joining alloy with pre-aging treatment,
7.2ks at 823 ° K and 36 at 823 ° K
Graph illustrating the result of examining the hardness distribution after aging treatment for ks, FIG. 3 is a graph illustrating the measurement result of the hardness distribution when performing aging treatment at 773 ° K after welding, FIG. 4 is a graph illustrating the results of examining the strength and toughness of the base material portion and the welded portion when the temperature of the second aging treatment is used as a variable.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryo Horiuchi 3-1-1 Yunodai, Sagamihara City, Kanagawa Prefecture Space Science Institute, Ministry of Education (72) Inventor Hiroo Shirasuna 7-1 Kioicho, Chiyoda-ku, Tokyo Sophia Univ. On-Campus (72) Inventor Akira Nosue 7-1 Kioicho, Chiyoda-ku, Tokyo Sophia University On-campus (72) Inventor Tadanori Okubo 7-1 Kioi-cho, Chiyoda-ku, Tokyo Sophia University On-campus (72) Inventor Seiji Ishimoto Kanagawa Prefecture Nissan Motor Co., Ltd. 2 Takaramachi, Kanagawa-ku, Yokohama (72) Inventor Hiroshi Sato 2 Takara-machi, Kanagawa-ku, Yokohama, Kanagawa

Claims (2)

[Claims] 1. V: 14.0 to 16.0% by weight, A
: 2.5-3.5%, Cr: 2.5-3.5%, S
When joining titanium alloys containing n: 2.5 to 3.5% as a basic component, the titanium alloys are pre-aged and then brought into contact with each other, and the contact portions have a high energy density heat source. A method for joining titanium alloys, characterized in that at least the welded portion is subjected to an aging treatment after being subjected to melt-joining. 2. The titanium alloy according to claim 1, wherein the temperature of the aging treatment applied to at least the welded portion is higher than the temperature of the preliminary aging treatment applied to the titanium alloy. How to join.