JPH01111834A - Low strength and high ductile ti alloy for cold working - Google Patents

Abstract

PURPOSE:To obtain a Ti alloy having sufficiently low strength and excellent ductility for cold working by alloying specific ratios of V, Sn and Zr to Ti. CONSTITUTION:The Ti alloy having the compsn. contg., by weight, 10-20% V, each 0.5-9.5% Sn and Zr as well as 1-10% their total amounts, or furthermore contg. 0.5-7% Al and the balance Ti is melted and refined to cast into the ingot. Said ingot is, e.g., heated to 700 deg.C, is hot rolled under 75% pressurizing ratio, is thereafter retained for 10 min to about 900 deg.C and is cooled by water. The Ti alloy having excellent low strength and ductility suitable to cold workability, particularly to cold forgeability and easily executable of cold working can be obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention is directed to a T having low strength, high ductility, and excellent cold workability.
This relates to i-alloy.

[Conventional technology] Ti alloys are light, strong, and have excellent corrosion resistance, so their use is gradually expanding, mainly in aircraft and space development equipment. Consideration has also begun to be given to using it as a component for manufacturing by processing. In order to perform cold working efficiently, it is necessary to have low deformation resistance and high ductility.

However, Ti-6A, which has been used in large quantities
α+β type Ti alloys represented by l-4V have poor ductility and are not suitable for cold working. Although β-type Ti alloys with improved workability than such α+β-type Ti alloys have been developed,
This is an improvement in cold rolling properties or sheet metal moldability where strength is not an issue, but does not reduce deformation resistance.In order to reduce deformation resistance, it is necessary to have low strength. However, even if the conventional β-type Ti alloy is tempered for cold working, its tensile strength is, for example, 90
A Ti-22V-4Al alloy with even lower strength has been developed (Japanese Unexamined Patent Publication No. 250138/1983).

[Problems to be solved by the invention] However, even with the above alloy, 80 Kgf/mm2
It has a tensile strength of about 100%, and it cannot be said that the strength is sufficiently low for cold working. For example, when cold forging such as upsetting forging is performed, the Ti alloy material is strongly restrained by the tool, so the deformation resistance increases rapidly.

As a result, even if the deformation resistance in tension differs by only a few kilograms,
During processing, the difference can be on the order of tens of kilograms.

Therefore, in order to maintain a good lifespan of the mold, it is necessary to reduce the deformation resistance of the forging material, for example, the above-mentioned tensile strength of 80 K.
It has been desired to develop a Ti alloy with even lower strength than that of about gf/mm2.

The present invention was developed under these circumstances, and its purpose is to further reduce the strength of Ti alloys than conventional Ti alloys, as well as improve drawability, which greatly affects the limit of cracking during processing. The object of the present invention is to provide a Ti alloy that has improved workability, particularly cold forgeability, and can be more easily cold-processed into parts.

[Means for solving the problems] The Ti alloy of the present invention contains 10 to 20% of V, 0.5 to 9.5% of Sn and Zr, and 1 to 10% in total, with the balance being Ti and unavoidable The gist is that it consists of impurities. In addition to the above structure, 0.5~
The content of 7% is also one of the important constituent elements of the present invention.

[Function and Examples] About 15% or more of V, which is a β stabilizing element, is added to Ti to
If quenching is carried out in the temperature range, a β single-phase Ti alloy can be obtained, but Ti alloys with a content of around 15% undergo stress-induced transformation or twinning deformation at room temperature, resulting in low deformation resistance. It is well known that there is a decline in However, according to the experiments conducted by the present inventors, even such a Ti alloy has a high tensile strength of 80 Kgf/ma+2, and its ductility is also not good, making it difficult to believe that it is fully suitable for cold working. is not.

Therefore, the present inventors have pursued and researched additive elements that can further reduce the strength and maintain good ductility while taking advantage of the effect of reducing deformation resistance caused by adding (■) to Tt. Layered. As a result, it was found that the intended purpose could be achieved by adjusting the V content to a range in which stress-induced transformation or twinning deformation occurs, and further containing a certain amount of Sn and Zr.

In order to investigate the appropriate addition range of these additive elements, the following experiment was conducted.

Button ingots of various alloy compositions shown in the left column of Table 1 (each 13
0g) was melted by tungsten arc melting method, and 70g
After 75% hot rolling at 0℃, 10% hot rolling at 900℃
The mixture was held for a minute and cooled with water. From this, the diameter of the parallel part is 2 mm
A series of tensile test specimens with a parallel length of 7 mm was taken and subjected to a tensile test at a strain rate of 20%/min to investigate the strength.
The 2% proof stress and tensile strength were measured, and the elongation and area of area were measured to investigate ductility. The measurement results are shown in the right column of Table 1.

Table 1 Based on the results shown in Table 1, the range of appropriate addition amounts of additive elements will be explained.

v: 10-20% When the amount of (1) added was less than 10%, martensitic transformation occurred during quenching, resulting in high strength and low ductility (Table 1 Nos. 10-12).

On the other hand, when it exceeds 20%, the strength is high because sliding deformation occurs completely outside the region where stress-induced transformation and twinning deformation occur (No. 26). As a result, it was concluded that in order to obtain the necessary effect of reducing strength and improving ductility, the amount of addition of (2) should be 10 to 20%. Furthermore, 12 to 18% was more preferable (No, 3.7).

Sn and zr: both 0.5 to 9.5% and total 1
Adding Sn or Zr in the presence of ~10% (1) could reduce strength and improve ductility; however, in this case, Sn and Zr
When both were added to coexist, their synergistic effect was observed, and the above effect was much more pronounced (No. 4).
and 17 or 18). It is believed that Sn and Zr further promote the β-stabilizing effect of V.

However, if the total amount of Sn and Zr added is less than 1%,
The strength increased and the ductility decreased compared to the case without additives (No.
, 15. 16 and 18 or 24 and 29). When the total addition amount was 1% or more, the strength began to decrease and the ductility began to improve. Then, when the addition amount reaches an extreme value of around 7%, the strength begins to increase and the ductility decreases.
Addition effects were observed if the amount added was 10% or less (N
o.

1-9). A more preferable addition amount is 2 to 8% in total. In addition, it is necessary to add Sn and Zr in an amount of 0.5% or more (see NO, 4 and 21).
%, both strength and ductility were insufficient (No,
4 and 22 or 1 and 13).

However, when the amounts of Sn and Zr added exceeded 10%, the strength sharply increased and the ductility decreased (see No. 2 and 14 or 6 and 19, 20, 23 or 9 and 25).

As is clear from the above results, N
Comparing Comparative Examples No. o, 1 to 9 and Comparative Examples 10 to 29 with the same V content, the strength of the present invention examples is more suppressed and the ductility is further improved. I found out that it was.

The present inventors further experimented and investigated the effect of adding Al on reducing strength and improving ductility. As a result, Sn or Z
It was found that adding Al without adding r improves ductility but also increases strength. Therefore, Sn and Zr
When a certain amount of Al was added to the Ti alloy according to the present invention, it was found that the strength could be further reduced, although the ductility was hardly affected. The tensile test piece in this case was prepared in the same manner as in the case without A1 added.

The alloy composition is shown in the left column of Table 2, and the experimental results are shown in the right column.

Based on the results shown in Table 2, the range of the appropriate amount of A1 to be added will be explained.

A1: 0.5-7% No. 30-32 are examples of the present invention, and Table 1 No.
Both the yield strength and tensile strength are lower by 0.2% compared to At.
Almost no effect of addition was observed, and in No. 35, the strength increased and the ductility decreased significantly. In other words, the effect of adding Al is sufficiently exhibited at an addition amount of 0.5%, but when the addition amount is 7%.
When the temperature exceeded 3, the martensitic transformation became noticeable during quenching, and it was not possible to reduce the strength (No. 3).
3 and 35).

For the alloy according to the present invention, 400°C, 45°c, s
After aging for 8 hours at oo℃ and 550℃, the Vickers hardness was measured, and the results showed that it had a high strength (more than 300 gf/mm2) equal to or higher than that of Ti-6Al-4V alloy.
It was confirmed that this can be obtained by selecting either of the aging treatments. That is, the Ti alloy according to the present invention can obtain strength characteristics equivalent to those of conventional Ti alloys if subjected to aging treatment.

[Effects of the Invention] Since the present invention is configured as described above, it has low strength and high ductility T which is extremely advantageous in performing cold working, especially cold forging, etc.
As a result, a Ti alloy with excellent properties can now be easily used not only in the aerospace industry but also in a wide range of consumer products.

Claims (2)

[Claims] (1) 10 to 20% V (meaning of weight %, same below),
0.5 to 9.5% of Sn and Zr each and 1 in total
A low-strength, high-ductility Ti alloy for cold working, characterized by containing ~10% Ti and the remainder consisting of Ti and unavoidable impurities. (2) V: 10-20%, Sn and Zr: 0.
5-9.5% and total 1-10%, Al 0.5-7
%, with the remainder consisting of Ti and unavoidable impurities.