JPH01111836A - Quench hardening type high strength ti alloy - Google Patents

Abstract

PURPOSE:To obtain a Ti alloy having excellent strength without subjecting it to an aging treatment and furthermore having excellent ductility by adding specific amounts of Cu and Al to Ti. CONSTITUTION:The ingot of a Ti-Cu-Al alloy contg., by weight, 3-12% Cu, 2-8% Al and the balance Ti is heated to about 750 deg.C and is hot rolled. Said rolled material is retained for 5min to about 900 deg.C and is thereafter subjected to water quench hardening. The above Ti alloy having <=140kgf/mm<2> strength without subjecting it to an aging treatment and furthermore having excellent ductility can be manufactured as hardened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a quench-hardening high-strength Ti alloy that exhibits high strength in its quenched state without undergoing aging treatment.

[Prior Art] Ti has three basic properties required as a structural material in the aerospace industry, the automobile industry, etc.: lightness, strength, and rust resistance. Therefore, Ti alloys that utilize these properties of Ti are expected to be used not only in the above-mentioned industrial fields but also in various other fields. However, although Ti alloy has such high utility value, there is a problem in that its strength is still not necessarily sufficient as a structural material. Therefore, in order to improve the strength, Ti alloys are subjected to solution treatment and quenching treatment, and then further subjected to aging treatment. Ti-6AI, which is widely used
Taking -4V as an example, it was about 120 gf/cm2 (about 100 Kgf/mm" if the above treatment was not performed).

In addition, N ea has a higher strength than these alloys.
rβ alloys are also being developed, and Ti-10V-2Fe-3AI, which is said to have the highest strength among them, has a strength of 140 gf/mu+'' after aging treatment.

[Problems to be Solved by the Invention] However, such prior art has the following problems.

(1) Aging treatment requires a long time, resulting in poor workability, and the strength increase effect obtained is only 20 Kgf/mm", which is not sufficient.

(2) It is difficult to obtain a material with a strength exceeding 140 gf/Inm2, and cannot sufficiently meet the demands of industry.

(3) According to AMS (Aerospace Materials Standard) 4989, it is stipulated that the elongation of the Ti-10V-2Fe-3AI mentioned above must be 4% or more, but when subjected to aging treatment, the elongation in the tensile test is almost negligible. It turns out to be a terrible photo.

The present invention was made under these circumstances, and is a quenched alloy that exhibits strength equal to or greater than that of conventional alloys that have been subjected to aging treatment, without being subjected to aging treatment, that is, in the quenched state. The purpose is to provide a hardening type high strength T1 alloy.

[Means for solving the problems] The present invention uses Cu: 3 to 12% by weight and Al: 2 to 8% by weight.
The gist is that the remainder consists of Ti and unavoidable impurities.

[Function] When Cu is added to Ti, the strength increases as the amount of Cu added increases, but the ductility decreases. On the other hand, when Al is added to Ti, the ductility improves as the amount of Al added increases, but the strength decreases.

The present inventors have conducted extensive research in order to obtain a Ti alloy that exhibits excellent strength without aging treatment and also has good ductility by adjusting the amounts of Cu and At added.

According to experiments conducted by the present inventors, when Cu is added alone to Ti, the amount of Cu added is approximately 6.5% (meaning % by weight).
(same below), the elongation and area of area in the quenched state become almost zero, and the tensile strength at that time is 110 Kgf.
/mm”, 0.2% proof stress is 102gf/rnm”
, and the ductility was 0.3%, both of which were insufficient (
Table 1 N, 20) described below. However, in addition to Cu, AI
It has been found that, depending on the amount of Al added, not only the ductility is improved, but also the strength (meaning tensile strength and 0.2% yield strength, the same applies hereinafter) can be maintained in an extremely excellent state. In other words, when the amount of Al added is less than 2%, the ductility is only slightly improved, and the strength is lower than that of AI.
This was the same as when no Al was added, and no significant effect of the addition of Al was obtained (N, 18 and 21). However, as is clear from the examples described later, when the amount of AI added is 2% or more, the ductility is excellent, and by appropriately selecting the amount of Cu added, the strength is also excellent. Ta. Especially when the amount of AI added is 3% or more, Cu
It has been found that depending on the amount of Ti added, it is possible to obtain a Ti alloy that maintains good ductility and has much higher strength than conventional examples. However, when the amount of At added exceeds 8%, it becomes excessively added, and even if the amount of Cu added is adjusted, it becomes brittle and elongation decreases (see comparison of N06 and 19.11 and 22). This seems to be caused by the appearance of Ti and AI phases.

From the above, the appropriate amount of Al to add is 2 to 8%.
In particular, it was found that 3 to 8% is more desirable in order to obtain a high-strength alloy (N01, 2.4, 5.8, and 9.12%).
and 13 for comparison).

On the other hand, according to the experimental results that tracked the effect of adding Cu, it was found that in order to obtain strength equal to or higher than that of conventional aging treated alloys, it was necessary to add at least 3% Cu (see below for implementation). (see example), the amount of added Cu is 12
%, it became impossible to maintain the ductility required for the structural member. The cause of this is that when the amount of Cu added is excessive, T
This is thought to be because intermetallic compounds such as i2Cu precipitate and the alloy structure becomes brittle.

Therefore, the appropriate amount of Cu to be added is 3 to 12%, and as will be clear from the examples below, in order to maintain sufficient ductility and obtain a Ti alloy with superior strength than conventional products, the amount of Cu to be added is 5 to 12%. It was concluded that a range of 10% to 10% is more preferable.

The metal structure of the present invention has a martensitic appearance. It is said that the martensitic structure does not contribute much to improving the strength of conventional Ti alloys. However, in the present invention, although no theoretical basis has been found, it seems that an extremely high-strength martensitic structure is obtained by the combination of Cu and AI.

Examples will be described below, but the present invention is not limited to the following examples, and it is within the technical scope of the present invention to make appropriate design changes in accordance with the spirit described above and below.

[Example] Tungsten arc melted 130g button ingots of various alloy compositions shown in the left column of Table 1, hot rolled at 700°C to approximately 75%, held at 900°C for 5 minutes, and then water quenched. I did this. From this, the parallel part is 2 mmψ, and the parallel part length is 8 mm.
A tensile test piece was taken and subjected to a tensile test at a strain rate of 20%/min to determine the 0.2% proof stress and tensile strength. Also,
Elongation from the test piece after fracture (gauge pressure ll!t near Cl1
1) was measured.

The results are shown in the right column of Table 1.

Table 1 As is clear from the test results in Table 1, Examples Nos. 1 to 5 and 8 of the present invention were not subjected to aging treatment, although they remained in the quenched state. Conventional Ti
An alloy with high strength comparable to that of the N ear β alloy was obtained, and the elongation was also extremely good at 7% or more. No again,
Nos. 13 and 14 exhibited much superior strength to conventional Ti alloys, and also had an elongation of 4% or more, satisfying AMS standards. Furthermore, for No. 6°7 and 9-11, the amount of Cu added is 5-10%.
.

Since the amount of AI added was 3 to 8%, which was the most preferable amount, not only did the alloy exhibit far superior strength to that of conventional Ti alloys, but it also had extremely good ductility. On the other hand, No
, Nos. 15 to 17, the amount of Cu added was insufficient, so that the strength required for a structural member could not be obtained. No, 2
In No. 3 and No. 24, the amount of Cu added was excessive, so the ductility necessary for a structural member could not be obtained. No. 18.20 and 2
In No. 1, the strength could not be improved because the amount of Al added was insufficient. Further, samples Nos. 19 and 22 became brittle due to the excessive amount of AI added.

[Effects of the Invention] Since the present invention is configured as described above, it has strength equal to or far superior to conventional aging treated alloys even without aging treatment, that is, even in the quenched state. Furthermore, it has become possible to provide a Ti alloy with extremely good ductility.

Claims (1)

[Claims] A quench-hardening type high-strength Ti alloy containing 3 to 12% by weight of Cu and 2 to 8% by weight of Al, with the remainder consisting of Ti and unavoidable impurities.