JPH0448055A - High strength heat treatment for titanium alloy - Google Patents

Abstract

PURPOSE:To improve the strength of a Ti alloy while securing its toughness by subjecting the above alloy with the prescribed composition to hot forming and then to aging treatment in a specific temp. region. CONSTITUTION:A Ti alloy having a composition consisting of 4.50-5.50% Al, 1.50-2.50% Sn, 1.50-2.50% Zr, 3.50-4.50% Mo, 3.50-4.50% Cr, <=0.15% O, and the balance essentially Ti is refined and cast into an ingot. This ingot is formed at 650-1,200 deg.C and then subjected to aging treatment at 350<600 deg.C. Further, it is desirable that, after the above forming, a stage of solution treatment at 790-810 deg.C is added prior to aging treatment. By this method, the strength of the Ti alloy can be improved while securing its toughness.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to titanium alloys, particularly -r; -51-2Sn.
-22r -4M0-4Cr alloy heat treatment method improvement. This heat treatment gives the alloy higher strength than previously available. [Prior art] Ti-51)-2Sn-2Zr-4Mo-4Cr
The alloy is a typical near-β type Ti alloy standardized by the number AMS4995, and is mainly used for manufacturing fan disks, blades, etc. for aircraft. Traditionally, processing and heat treatment of this alloy involves hot or warm forming followed by solution treatment at temperatures around 800°C, followed by processing at temperatures of 600-650°C, typically 635°C. The process of age hardening was followed. When it comes to aircraft parts, weight reduction is a constant requirement. It is also desirable to improve the strength of this material while ensuring its toughness, thereby producing lighter parts. [Problems to be Solved by the Invention] An object of the present invention is to meet the above-mentioned demands regarding titanium alloys and to realize a heat treatment method that provides a material with higher strength than conventional solution-aged materials. [Means for solving the problem] The high-strength heat treatment method for titanium alloy of the present invention has Aj: 4.50.
~5.50%, Sn:1.50~2.50%, Zr
:1.50~2.50%, MO:3゜50~4.50%
, Cr: 3.50-4.50% and O: 0.15%
A titanium alloy containing the following, with the remainder substantially consisting of Ti, is formed in a temperature range of 650 to 1200°C, and then subjected to aging treatment in a temperature range of 350°C or higher and lower than 600°C. In the above treatment method, a step of solution treatment at a temperature of 790 to 810° C. may be added after the molding process and prior to the aging treatment.

[For use]

The titanium alloy to be heat-treated in the present invention has almost the same composition as that standardized as AMS4995 as mentioned above, except for the 0 content, which has an upper limit of 0.15% (standard is 0.13%). It is expanded to. This is because the purpose was to improve strength, but since increasing the O content reduces toughness, 0.15% was chosen as a compromise. The reason why the lower limit temperature for hot working is set at 650° C. is that at temperatures lower than this, the titanium alloy has low deformability and high deformation resistance, making processing difficult. On the other hand, when processed at high temperatures, a recovery recrystallization phenomenon occurs, making it difficult for processing strains to remain, and in directly aged materials, the aging effect is weakened. High temperatures also lead to coarsening of grains,
Ductility decreases after aging. Age hardening was conventionally carried out at 600 to 650°C, but in the present invention, age hardening was carried out at a temperature of 350°C or higher, 600°C or lower.
The temperature below ℃ was adopted. The lower limit of 350°C is because aging takes an excessively long time at lower temperatures, which is impractical, and the upper limit of 600°C is because the strength decreases due to over-aging, and the effect of heat treatment is lost. This is to avoid being abused. The solution treatment temperature of 790 to 810°C is the same as the conditions conventionally employed. If the temperature is lower than 790°C, the melt penetration of the alloy components is poor, and if the temperature exceeds 810°C, the α grains become coarse and unevenly dispersed, resulting in a decrease in toughness and, as a result, cracks are likely to occur.

[Example 1] A titanium alloy having the following composition was produced by melting in a vacuum arc furnace and cast into an ingot of 100 kg. Ti-4,89AJ! -1,95Sn -1,80
Zr-4,05MO-3,75Or-0,06(0)
This ingot was bloomed at 1100°C to form a round bar with a diameter of 65 ann, and hot rolled at 1000°C to obtain a 19#I wire rod. The rolling end temperature is about 700°C. Some of the wire rods were solution-treated at 800"CX for 4 hours and water-cooled, and some were left as they were without solution treatment.
Aging treatment was performed under conditions of heating and air cooling for 8 hours at various temperatures within the range of 0 to 700°C. A tensile test was conducted on each sample material. The 0.2% proof stress and tensile strength are shown in FIG. 1, and the elongation and reduction of area are shown in FIG. From the data in the figure, approximately 160Kgf is obtained by low-temperature aging treatment.
It can be seen that a tensile strength of 2/2 was achieved. This value is 1, which was previously considered to be the standard performance for this material.
It can be said that this is a clear improvement compared to 20 K9 f /1rvn2. Low-temperature aging is effective in improving yield strength by 0.2% in directly aged materials, with a maximum yield strength of 150 K'j f/s.
Reach 2.

Example 2 A titanium alloy having the following composition was produced by melting in a vacuum arc furnace and cast into a 1100N ingot. This ingot was bloomed at 1100℃ and the diameter was 65! r
I! I made it into a round bar of n. Ti-4,89AI-1,95Sn-1,80Zr
-4,05MO-3,75Cr -0,06(0) This round bar was hot rolled under the conditions shown in the table to form a wire rod with a diameter of 19#l. After each wire rod was heat treated under the conditions shown in the table, a tensile test was conducted. The results are also shown in the table. [Effects of the Invention] According to the treatment method of the present invention, it is possible to improve the strength of AM34995 type titanium alloy while ensuring its toughness. As a result, mechanical parts can be made even lighter and have higher performance (such as being able to rotate at higher speeds). Therefore, the present invention is applicable to aircraft parts as described above, as well as
Contributes to the production of automobile parts such as connecting rods, valves, and springs.

[Brief explanation of the drawing]

All drawings are data of embodiments of the present invention, and the first
The figure is a graph showing 0 and 2% yield strength and tensile strength at various aging temperatures, and FIG. 2 is a graph showing elongation and reduction of area at various aging temperatures. Patent Applicant Daido Steel Co., Ltd. Agent Patent Attorney Souo Suga No. 1! ! 1

Claims (2)

[Claims] (1) Al: 4.50~5.50%, Sn: 1.50~
2.50%, Zr: 1.50-2.50%, Mo: 3.
A titanium alloy containing 50 to 4.50% Cr, 3.50 to 4.50% Cr, and 0.15% or less O, with the remainder substantially consisting of Ti, is formed in a temperature range of 650 to 1200°C. A high-strength heat treatment method for titanium alloys, which comprises aging treatment in a temperature range of 350°C or more and less than 600°C after processing. (2) After molding and prior to aging treatment, 790 to 8
The high-strength heat treatment method according to claim 1, further comprising a step of performing solution treatment at a temperature of 10°C.