JPS6160871A - Manufacture of titanium alloy - Google Patents

Abstract

PURPOSE:To manufacture a Ti alloy having superior strength and toughness by subjecting a Ti alloy to multistage working in which the working temp. in the succeeding stage is made lower than the working temp. in the preceding stage and rapid cooling is carried out every time a working stage is finished and by subjecting the worked Ti alloy to conventional heat treatment. CONSTITUTION:When a superplastic Ti alloy material, a high strength and toughness forged or rolled Ti alloy article or the like is manufactured, a Ti alloy is subjected to multistage working. In the multistage working, the working temp. in the succeeding stage is made lower than the working temp. in the preceding stage, the final working temp. is made as low as possible, and rapid cooling is carried out every time a working stage is finished. The cooling rate is made as high as possible to make the grains fine and to increase the strength. The worked Ti alloy is subjected to conventional heat treatment by soln. heat treatment and aging to improve the toughness.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing titanium alloys, and is particularly advantageous for producing titanium alloy superplastic materials, high-strength and high-toughness titanium alloy forged products, rolled products, etc. relates to a method applicable to

(Prior art) The production of titanium alloy forged products, rolled products, etc. is usually carried out at a temperature below the β-transformation point (varies depending on the material), and when a particularly high toughness value is required, There is a method of performing the process at higher temperatures.

However, in all of these methods, the crystal grains are coarse (@
In the former case, the toughness is low, and in the latter case, the toughness improves but the strength decreases (
(approximately 10% compared to the former) occurs.

(Problems to be Solved by the Present Invention) The present invention provides a method for producing a titanium alloy that eliminates the drawbacks of the above-mentioned conventional methods, refines crystal grains, and improves strength and toughness as a result. This is what I am trying to do.

(Means for Solving the Problem) The present invention provides multi-stage processing in which the processing temperature of the subsequent stage, such as forging temperature or rolling temperature (hereinafter simply referred to as processing temperature), is lower than the processing temperature of the previous stage and is rapidly cooled at the end of each processing step. The method for producing a titanium alloy is characterized in that a conventional heat treatment is performed after the multi-stage processing.

Refining grains is usually done by increasing the amount of processing, but in the present invention, the processing temperature in the latter stage is lower than the processing temperature in the previous stage, and two or more stages are used in which the processing temperature is rapidly cooled after each processing step. According to the processing method, even finer crystal grains can be obtained compared to the conventional method for the same amount of processing. It is the same as before that the larger the processing amount is, the more advantageous it is, but when processing 60 inches, the processing is divided into at least 2 times, preferably 3 to 5 times, and after processing, it is rapidly cooled and the final It is preferable that the processing be carried out at the lowest temperature possible.

Generally, when crystal grains are made finer, strength improves, but fracture toughness (hereinafter referred to as toughness) decreases. However, the present invention improves strength and toughness by refining crystal grains through the above-described special processing and combining this with heat treatment.

In a preferred embodiment of the present invention, the final machining temperature is set to be above the β-transformation point, and an appropriate amount of the β-transformation temperature or below is combined, and quenching is performed after each process. In particular, the processing below the β-transformation point is performed by the above-mentioned split processing, The final processing should be carried out at the lowest temperature possible.
This makes it possible to refine the crystal grains and improve lCa properties at the same time.

Note that the purpose of the rapid cooling performed after each of the above processing is to precipitate fine acicular martensite and to keep the internal stress high, and the faster the cooling rate, the more effective it is in grain refinement. big.

In the present invention, normal heat treatment is performed after the above processing. Although this heat treatment differs depending on the material, it is basically a solution treatment and an aging treatment, and this heat treatment results in a microstructure in which an initial α phase crystallizes in a β-matrix. Note that if the solution treatment is performed in two or more stages, the α phase precipitated from the β phase will grow, and the toughness can be improved. However, since toughness and strength are contradictory properties, it is not possible to improve them proportionately, so solution treatment is not necessary.
If a large number of stages are used, the toughness will improve, but the strength will decrease, so the heat treatment conditions (select) depending on the desired toughness and strength.

Titanium alloys to which the method of the present invention can be applied include α-type and α+
Both β-type and β-type are available, and α-type is pure Tej17,
Ti-5A4-458n (including CELI (a material with few impurities)), TiTi-8Aj-IV-1, etc. are α+β types such as Ti-6At-4V (including ELI), Ti-6At-6v-29n% Ti, -7At
-4Mo.

TiTi-6A4-2EIn-42r-2, T1-6mut-28n-4Zr-6Mo, etc. are Beta as β type.
pi (Ti-j 1.5Mo-6Zr-4,5Sn
)? 1-3At-87-60! r-4Mo-4Zr
.

Ti-10V-21'e-3muL% Ti-13'7-
11or-5mmL.

Examples include Ti-157-3Or-3 and L-38n.

(Example) Example 1 Regarding T1-6Mo A-28n-42r-6Mo alloy,
The treatment according to the present invention was carried out under the conditions shown in FIG.

In addition, in the figure, 1 and 2.5 are casting processing, and WQ is water cooling. A.C.
is air cooled, 930℃XIHWQ, is solution treated, 595℃
X 611AO indicates aging treatment.

For comparison purposes, commercially available forged products of the above alloys [those made below the β-transformation point, with a forging ratio of about 1.7 (about 70%) at the billet stage, and a subsequent forging ratio of 2 or more] , heat treated under the same conditions as above (hereinafter referred to as conventional).

These results are shown in Figure 2 (according to the method of the present invention).
It is shown in the micrograph of Figure 2 @) (conventional).

The crystal grain size of the product according to the method of the present invention shown in Fig. 2 CA) is 1 to 3.
The conventional crystal grain size (μ, in FIG. 2) was 20 to 30 μ.

In addition, the strength characteristics of the above method of the present invention and the conventional method are shown in the table below.

Table 1 Example 2 The purpose was to manufacture a superplastic material, and the experiment was carried out as follows.

The same alloy used in Example 1 was treated according to the present invention under the conditions shown in FIG. Note that in the figure, 1.2 is forging processing, and 1.2 was forged by 35% each out of the 7096 working amounts. WQ is water cooling, AC is air cooling, 950℃X 1H
WQ indicates first-stage solution treatment, 800°C XIHW (J indicates second-stage solution treatment, and 593°C x 6HAC indicates aging treatment.

For comparison, commercially available forged products of the above alloys [one made at a temperature above the β-transformation point and one made at a temperature below the β-transformation point for 2 hours] were used.
, and the forging ratio is the same as the commercially available forged product used in Example 1]
The results were heat-treated under the same conditions as above (hereinafter referred to as "conventional"). The conventional type in the following cases) is shown in the class 8 & mirror photograph of Fig. 4(C) (the conventional type in the case of β-transformation point or higher).

Fig. 4(A), crystal grain size 1 to 3 obtained by the method of the present invention
μ, Figure 4) The conventional type has a grain size of 20 to 30 μ,
The conventional one shown in FIG. 4(0) had a crystal grain size of 20 to 50 μm.

The strength characteristics of these materials are also shown in the table below.

Table 2

[Brief explanation of the drawing]

Figures 1 and 3 are diagrams showing processing (forging) and thermogeographical conditions in examples of the present invention, and Figures 2 and 4 are microscopic photographs of metal structures obtained in examples of the present invention. . Sub-agent 1) Post-Morning agent Ryo Hagiwara - Figure 1 1 + Ginma 3 Figure □ Time page 2 Figure (c) (2)
x50D x500 children 4
Figure (A) (8) (C)

Claims (1)

[Claims] A method for producing a titanium alloy, characterized by multistage processing in which the processing temperature in the subsequent stage is lower than the processing temperature in the previous stage, in which the processing temperature is quenched at the end of each processing step, and ordinary heat treatment is performed after the multistage processing.