JPS60184668A - Heat treatment method for titanium alloy - Google Patents

Abstract

PURPOSE:To manufacture a Ti alloy for high temp. service having superior ductility and strength by hot working an alpha+beta type Ti alloy and subjecting it to soln. heat treatment, water hardening, process annealing and aging under specified conditions. CONSTITUTION:An ingot of an alpha+beta type Ti alloy for high temp. service such as Ti-6Al-2Sn-4Zr-2Mo is cast, hot worked, and subjected to soln. heat treatment at 960 deg.C for 1hr, water hardening, process annealing at 750-800 deg.C for <=1hr and aging by holding at 593 deg.C for 8hr. Hardening is carried out by the aging to manufacture a Ti alloy for high temp. use having superior mechanical properties such as strength and ductility.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Applicability The present invention relates to a method for heat treating titanium alloys for high temperature use. More specifically, the present invention relates to a method of heat treating a high temperature α-decade titanium alloy to produce a high temperature titanium alloy that maintains ductility and has improved strength.

BACKGROUND OF THE INVENTION Various methods have been developed and used for heat treatment of high-temperature titanium alloy bars and the like.

For example, Aerospace Material Sp
The heat treatment method disclosed in specification AMS4975B is to hold titanium alloy rods, wires, flash welding ring materials, etc. at a temperature of 14°C ± 8.3 below βtransus for 1 hour, cool with air or at a higher rate, and then It is subjected to an aging treatment held at a temperature of 593.3°C±8.3°C for 8 hours, and then air-cooled.

Similarly, Aerospace, Material
5peeificat, ion AMS4976A,
The forged material is heated to a temperature in the range of 15 to 30°C below βtransus, held at a predetermined temperature within the permissible range of ±8°C for 60±5 minutes, cooled in air or at a rate faster than steam, and then heated to a temperature of 593±8°C. A method for heat treating a forged material is disclosed, which comprises subjecting the forged material to an aging treatment maintained at a temperature of 8.degree.

Furthermore, Metals and Ceramics in the United States
Information [Tit issued by enter
anium 81loy Handbook” (12
For rods and forgings with a diameter of less than 2.5 inches, they are heated at approximately 954°C for 1 hour and then air cooled to approximately 59°C.
Heat at 4°C for 8 hours, then air cool; - For rods and forgings with a blade diameter of 2.5 inches or more, the temperature is approximately 899°C or 95°C.
A heat treatment method is disclosed in which the material is heated to 4° C. for 1 hour, air cooled, heated to about 594° C. for 8 hours, and then air cooled.

According to the document, the mechanical properties at room temperature of the article heat-treated according to the third method are as shown in Table I below.

Proof strength 89Kg/mm2 Tensile strength HIOKg/mm2 Elongation 15% Reduction of area 25% As can be understood from the results in Table I, the conventional method can also achieve a considerable improvement in mechanical properties, but the ductility at room temperature Developing a heat treatment method that further improves mechanical strength without sacrificing strength is of great significance in maintaining strength at high temperatures.

Purpose of the Invention The present invention has been developed in view of the current state of the conventional methods as described above.
The object of the present invention is to provide a heat treatment method that can increase the strength of a β-type titanium alloy without reducing its ductility.

Structure of the Invention As a result of various studies and research to develop a new heat treatment method for α+β type titanium alloy, the present inventor discovered that it is possible to use water cooling for cooling after solution treatment and to perform intermediate annealing before the aging heat treatment process. We found that it is advantageous to further improve the mechanical strength of high-temperature α+β type titanium alloys than before, and based on this knowledge, we completed the present invention.

That is, in the heat treatment method for high-temperature α+β type titanium alloy according to the present invention, the titanium alloy is hot-worked, then subjected to solution treatment, water-cooled, and treated at a temperature of 750 to 800°C for at least 1 hour. It is characterized by performing intermediate annealing by holding for a period of time and cooling in air, and further performing aging heat treatment according to a conventional method.

α+β type titanium alloy to be subjected to the heat treatment method of the present invention -C is 'ri-68l-'2Sn -4Zr -2M
o (6・2・4・2), T1-6AI −
2Sn-, 4Zr-6M.

(6・2・4・6), Ti-8AI-IMo
-I V (8.1.1), etc., and the same effect can be expected for any of them.

Further, the shape of the article to be processed is not particularly limited, and examples thereof include a rod 1, a wire, a link shank, a forged material, and the like.

Since the α+β type titanium alloy that is the object of the present invention is a heat-resistant alloy, it is desirable that the decrease in mechanical strength under high-temperature conditions is small.

Therefore, the inventor of the present invention sought to improve the strength of the product after heat treatment.
For the purpose of solution treatment, the material to be treated is heated to a solid solution range, sufficiently maintained at this temperature, and then rapidly cooled in a stirred water at room temperature. It was water quenched. Incidentally, in the conventional method, the quenching was performed by air cooling as described above. After this rapid cooling treatment, the treated product is generally hardened by aging heat treatment according to conventional methods.

However, the above-mentioned rapid cooling treatment by water quenching tends to reduce the ductility of the treated product. Therefore, in order to achieve the intended purpose of improving the strength without sacrificing the ductility of the present invention, some kind of device must be devised between the quenching step after the solution treatment and the subsequent aging heat treatment step. There is a need.

The present inventor has found that the following intermediate annealing process is extremely effective in preventing the decrease in ductility due to water quenching. That is, the intermediate annealing step of the present invention is performed at 750 to 800°C.
temperature for at most one hour, and then air-cooled to room temperature. The temperature of the intermediate annealing step is critical for achieving the above-mentioned purpose, and even if it is lower or higher than the above-mentioned range, it is unsatisfactory for preventing a decrease in ductility due to water quenching. In addition, intermediate annealing exceeds 1 hour.
Even if it is implemented, it is meaningless from an economic point of view since it is hardly expected to increase the above effect. Further, since the intermediate annealing time varies depending on the size, amount, etc. of the material to be treated, there is no particular restriction on the lower limit of the time. However, in general, by holding the annealing temperature for 10 to 20 minutes, the desired effect can be expected.

In the heat treatment method of the present invention, the titanium alloy product after the intermediate annealing treatment is subjected to aging heat treatment under the same conditions as in the conventional method, that is, held at about 593° C. for 8 hours, to thereby obtain a final product.

Effects of the Invention According to the novel heat treatment method for high-temperature α-10β type titanium alloy of the present invention, cooling after solution treatment is water quenching, and between the water quenching and aging heat treatment step, 750 to 800
The strength of the titanium alloy can be increased to a large rlJ without sacrificing ductility due to the intermediate annealing treatment, which consists of holding at a temperature of
It became possible to increase the That is, the products treated by the method of the present invention have almost no change in ductility even though the yield strength is improved by 10 kg/mm2 or more compared to the products treated by the conventional heat treatment method. Thus, according to the method of the present invention, it is possible to obtain a titanium alloy with better heat resistance than that obtained by the conventional method, and therefore, the heat treatment method of the present invention can be said to be an extremely significant invention industrially.

Hereinafter, the heat treatment method of the present invention will be explained in more detail with reference to Examples. In addition, as a comparative example, results obtained by a conventional method are also shown to clearly demonstrate the effects of the present invention. These embodiments are merely illustrative, and the present invention is not limited by any of the embodiments.

As an example sample, Ti=6'Al-2Sn-4Zr, -2
Mo (6・2・4・2) alloy (15 medium x 90 mm
Using the forged and drawn bar material of Q), heat treatment was performed under the conditions shown below according to the method of the present invention and a conventional method to produce heat-resistant titanium alloy forest material.

FIG. 1 and FIG. 2 are heat treatment diagrams showing the heat treatment steps according to the present invention and the conventional method, respectively. However, in these figures, AC means air cooling and WQ means water quenching.

The thus-circled sample was subjected to a tensile test with a yield strength of
Tensile strength, elongation and area of area were measured. The results are shown in Table 1 and Table 111 below.

Table ■: Comparison of mechanical properties (room temperature) From the results in Tables ■ and ■, it can be seen that the products treated according to the method of the present invention have a yield strength and tensile strength of 10 kg/mm2 at room temperature that are higher than the products obtained by the conventional method. To a high degree,
It can be seen that despite the considerable improvement in strength, the elongation and reduction of area are equal or even better. It can also be seen that the strength is superior to that of the conventional method even at high temperatures.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 illustrate the present invention and the conventional heat treatment method in Examples, respectively. Patent applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Masahiko Arai Figure 1 Figure 2

Claims (1)

[Claims] (1) After hot-working a high-temperature α-10β type titanium alloy and subjecting it to solution treatment, it is water-cooled, held at a temperature in the range of 750 to 800°C for less than 1 hour, and then air-cooled to perform intermediate annealing. conduct,
A heat treatment method for a high-temperature α+β type titanium alloy, which is then subjected to an aging treatment.