JPS63223155A - Production method of α+β type titanium alloy extrusion material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention has excellent strength, ductility, and toughness, and when applied to aircraft structural members, etc., it is possible to further improve their performance. The present invention relates to a method for producing α+β type titanium alloy extruded material, which enables stable production of "shaped materials", "tube materials", etc. on an industrial scale.

Background technology α+β type titanium alloys have not only excellent toughness but also good strength, workability, formability, and weldability, so they have high specific strength and excellent corrosion resistance. Among the titanium alloys that are attracting attention, they are in the greatest demand as structural members for aircraft and various equipment and devices.In order to use these structural members, the material is usually shaped into the desired shape by extrusion molding. It has been shaped into

By the way, α+β type titanium alloys are generally formed by extrusion in a temperature range above the β transformation point where deformation resistance is low, but extruded materials formed in the β single-phase region have “0.
There was a problem in that the α+β type extruded materials were all low in terms of 2% proof stress and ductility.

Therefore, we solved these problems and provided a member with sufficient strength, ductility, toughness, etc.
A method of extrusion molding a 4V titanium alloy in the α+β region of 850 to 960°C was proposed (Japanese Patent Application Laid-open No. 193719-1983).
issue).

However, as is clear from Figure 1, which shows the relationship between processing temperature and deformation resistance of α+β type titanium alloy, α+β
In the temperature range (850 to 960°C), the deformation resistance is still high, which limits the dimensions and processing rate of extruded products, making it difficult to manufacture products with complex shapes.

<Means for Solving the Problems> The present inventors have solved the above-mentioned problems regarding extrusion molded products of α+β type titanium alloys, and have developed α+ type titanium alloys that have excellent strength, ductility, and toughness.
In order to stably manufacture β-type titanium alloy extrusion products without any particular restrictions on shape or dimensions, we conducted research from various perspectives and obtained the knowledge shown in (al to (d)) below. (a) In order to ensure sufficient strength, ductility, and toughness for α+β type titanium alloy extruded products, the microstructure of the final product must be modified to have “extremely fine grains in the fine β grains”. It is important to create a state in which acicular α exists, and if the final shape of the extruded product has the above microstructure, an α + β type titanium alloy member with good strength, ductility, and toughness can be realized. bl However, it is extremely difficult to obtain fine β grains by extrusion molding in the β region where deformation resistance is low, but unexpectedly, it is possible to apply sufficient processing at the time of manufacturing the extruded material billet. If we use a material with a "fine equiaxed α+β structure" that can be easily achieved by extrusion and take appropriate measures after extrusion, sufficiently fine recrystallized β grains can be obtained even by β region extrusion. It is possible to realize a microstructure in which extremely fine acicular α particles are precipitated in eight fine grains, and (C) “β grain boundaries, which are a factor that suppresses the growth of recrystallized β grains and reduces ductility. In order to suppress the "precipitation of α phase into the material," as mentioned above, it is necessary to take appropriate measures after extrusion molding, but this treatment must be a means of "quenching immediately after extrusion molding." (d ) The microstructure obtained by the above rapid cooling is a mixed structure of martensite (α') and acicular α+β, but there are extremely fine β grains in the fine β grains that exhibit sufficiently high ductility and toughness. In order to realize a "microstructure in which acicular α exists," it is necessary to subject the extruded material after the rapid cooling to annealing under predetermined conditions to decompose martensite (α').

This invention was made based on the above knowledge, and more than 50% of the processing is performed in the α+β region, resulting in fine equiaxed α+
An α+β type titanium alloy billet with a β structure is heated to a temperature between the β transformation point and [β transformation point + 150°C], and the extrusion ratio is 1.
Extrusion processing of 0 or more is performed, followed by cooling to 500 °C or less at a cooling rate of 5 °C / sec or more, and then 70 °C
By annealing at a temperature of 0 to 850°C for 0.5 to 4 hours, α+β has excellent strength, ductility, and toughness.
This invention is characterized by the fact that it is possible to easily and stably manufacture type titanium alloy extruded materials even if they have complex shapes and dimensions.

In addition, in the method of this invention, the reason why the extrusion conditions were limited as mentioned above will be explained.

A) Applicable extrusion billet We decided to use a billet for extrusion molding that has a fine equiaxed structure that has been processed by 50% or more in the α+β region because if the processing rate in the α+β region is less than 50%, The structure of the billet cannot be made into the desired fine equiaxed α+β structure, but becomes an acicular or plate-like α+β structure, and even if a billet with such a microstructure is extruded, fine recrystallized β This is because grains cannot be obtained.

B) Heating temperature during extrusion Extrusion in a temperature range below the β transformation point not only has high deformation resistance, but also reduces the ability to achieve the “microstructure in which extremely fine acicular α particles are precipitated within fine β grains” that this invention aims for. Therefore, the toughness cannot be improved. On the other hand, [β transformation point +150℃]
If extruded at a temperature exceeding 0.2%, the yield strength, ductility, and toughness will deteriorate, and a good product will not be obtained due to surface roughness due to surface oxidation. Therefore, the heating temperature during extrusion was limited to the range from the β transformation point to [β transformation point +150'c].

C) Extrusion Ratio If the extrusion ratio is less than 10, recrystallized β grains will grow during processing, resulting in a 0.2% deterioration of yield strength, ductility, and toughness. Therefore, the extrusion ratio was limited to 10 or more.

D) Cooling rate after extrusion and end temperature of quenching The cooling rate from the extrusion temperature was set at 5°C/sec or more to suppress the growth of β grains during cooling and to prevent the formation of grain boundaries during cooling. This is to suppress the precipitation of coarse α phase, and the cooling rate is 5℃.
This is because if it is less than /second, the above-mentioned suppressing effect will not be sufficient. Moreover, if the quenching end temperature exceeds 500℃, β
There is a risk of grain growth and coarse alpha phase precipitation. Therefore, immediately following the end of extrusion, the cooling rate is 5°C/sec or more to
It was decided that the temperature should be cooled to below 0°C.

E) Annealing conditions As explained earlier, the microstructure of the extruded material after cooling is a mixed structure of (α'+α+β), but α'
The presence of fumarunsite in the final product results in a significant decrease in toughness. Therefore, the extruded material after cooling needs to be annealed at a temperature of 700 to 850°C for 0.5 to 4 hours to decompose α' fumarunsite, but if the annealing temperature is less than 700°C, If the annealing time is less than 0.5 hours, α
′-α+β decomposition did not proceed sufficiently, and on the other hand, the annealing temperature was 8.
If the temperature exceeds 50°C or the annealing time exceeds 4 hours, the α phase produced by the decomposition of α'-α+β grows, making it impossible to obtain the desired strength and toughness.

Next, the present invention will be specifically explained using examples and comparing with comparative examples.

<Example> Example 1 A piece with a diameter of 400 mmφ obtained by vacuum arc melting
After β forging and α+β forging were performed on a Ti-6Al-4V alloy ingot having the composition shown in Table 1 (α+β
The degree of forging is shown in Table 2), diameter: 170nφ
It was made into a billet for extrusion.

Next, this billet was extruded under the conditions shown in Table 2 and annealed to produce an L-shaped material.

The mechanical properties of the obtained mold material were investigated and the results were used in the second
It is also shown in the table.

As is clear from the results shown in Table 2, the shape material produced under the conditions of the present invention exhibits excellent values for both strength, ductility, and toughness, whereas It can be seen that a product that does not satisfy the conditions of the invention does not satisfy all of the above characteristics.

Example 2 The diameter was 40011φ obtained by vacuum arc melting.
So, Ti-6Aj with the component composition shown in Table 3? -6V-
After subjecting the 2Sn alloy ingot to β forging and α+β forging (the working degree of α+β forging is shown in Table 4), the diameter:
A billet for extrusion with a diameter of 160 mm was prepared.

Next, this billet was extruded under the conditions shown in Table 4 and annealed to produce seamless steel pipes.

The mechanical properties of the obtained seamless steel pipe were investigated, and the results are also shown in Table 4.

The results shown in Table 4 also show that the seamless steel pipe manufactured under the conditions of the present invention exhibits excellent values for strength, ductility, and toughness, whereas any of the manufacturing conditions of the present invention It is clear that those that do not satisfy the conditions are inferior in any of the above characteristics.

In addition, in Examples 1 and 2, Ti-6AI! -4V alloy and Ti-6Aj? -6V -2Sn alloy has been explained, but other α+β type titanium alloys, such as Ti-3A I-2,5V alloy, Ti-6A
j! -2Sn-42r-2Mo alloy or Ti6
Aj! It goes without saying that fully satisfactory results can be obtained with -2Sn -42r -6MO alloys and the like.

Summary of effects> As explained above, according to the present invention, strength.

α+β has extremely excellent performance in terms of ductility and toughness.
It is possible to stably manufacture titanium alloy extruded materials with high efficiency regardless of the product shape and size, and it is possible to produce α+β type titanium alloy parts at a low cost that fully satisfy the increasingly strict performance requirements for materials such as aircraft fuselage materials. Its industrial significance is extremely great, as it can be provided at a low price.

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[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between processing temperature and deformation resistance of α+β type titanium alloy.

Claims (1)

[Claims] 50% or more of processing is performed in the α+β region to create a fine equiaxed α+
An α+β type titanium alloy billet with a β structure is heated to a temperature between the β transformation point and [β transformation point + 150°C], and the extrusion ratio is 1.
Extrusion processing of 0 or more is performed, followed by cooling to 500 °C or less at a cooling rate of 5 °C / sec or more, and then 70 °C
A method for producing an α+β type titanium alloy extruded material, characterized by performing annealing at a temperature of 0 to 850°C for 0.5 to 4 hours.