JPS62120468A - Manufacture of titanium alloy material excellent in strength and ductility - Google Patents

Abstract

PURPOSE:To easily manufacture a Ti alloy material excellent in mechanical properties such as strength, ductility, etc., at a low cost by applying hot working to a stock having a specific composition consisting of V, Cr, Sn, Al, and Ti under proper conditions. CONSTITUTION:In manufacturing Ti alloy material consisting of, by weight, 14-16% V, 2.5-3.5% Cr, 2.5-3.5% Sn, 2.5-3.5% Al, and the balance Ti with inevitable impurities and further containing, if necessary, <=0.3% O, a stock for hot working is heated to 900-1,050 deg.C and then working is started. Successively, above-mentioned working stock is subjected to working at >=50% draft at a temp. between the beta-transformation point and 900 deg.C, where at >=30% draft at a temp. between the beta-transformation point and 850 deg.C, followed by rapid cooling from a temp. of beta-transformation point or above to 400 deg.C or below at a cooling rate of >=2 deg.C/sec. In this way, Ti-15V-3Cr-3Sn-3Al alloy material having superior mechanical properties and structure can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a method for producing a titanium alloy material that has poor mechanical properties such as strength and ductility.

[Prior art and its problems I Ti-15V-3Cr-3Sn-3A, Q alloy has high strength and good cold workability, and its use as a β-type titanium alloy has recently been expanding. This means that the titanium alloy changes to α+β such as Ti-6All-4V alloy. This is because cold workability is significantly superior to that of titanium alloys, and cold pressing and the like can be employed, resulting in labor savings of approximately 1 J-.

However, the above Ti-15V-3Cr-3Sn
-3AJ alloy material (hereinafter referred to as the present alloy material) has been difficult to manufacture using a hot working process.

This is because the non-uniformity of mechanical properties and structure was a bottleneck in the production of this alloy material, and it was considered difficult to obtain sufficient mechanical properties and uniformity of structure using only hot-tempered steel.

Therefore, this alloy material is rarely used as is after the hot working process, and in the past, it was generally produced through a three-step process: hot working process - solution treatment - cold working process, and then the hot working process. By adding a subsequent cold working step, the aim was to improve the mechanical properties and the uniformity of the mechanical properties and structure.

However, this method requires a large number of steps and is not easy to manufacture, resulting in problems in productivity and -F production cost.

[Means for Solving the Problems] The present invention was created through repeated research and experiments in order to solve the above-mentioned conventional problems. To provide a method for easily producing the present alloy material having excellent mechanical properties and structure equivalent to the conventional method (hot working culm - solution treatment step - cold working 1 culm). be.

In order to achieve this goal, the present invention provides a method for manufacturing the present alloy material, especially for hot processing materials (slabs, billets, etc.).
This is a method in which processing is performed by strictly controlling the heating temperature and hot working conditions, and rapid cooling is performed strictly at 1IIJTi1 after hot working.

That is, the feature of the present invention is that V:14 to IG
wt%, Cr: 2.5-3.5wt%, Sn: 2
．． 5-3, 5wt%, A, Q: 2.5-3.5w
When producing a titanium alloy material consisting of t%, the balance Ti and unavoidable impurities, the material for hot working is heated to a temperature of 4900°C or higher and 1050°C or lower, and at least the β transformation point or higher and 900°C or lower. 50% or more of processing at a temperature above the β-transformation point and below 850°C, followed by further processing] The purpose is to perform cooling η at a cooling rate of c2°C/sec or higher.

With this method, only a hot working process is required without adding a cold working process, and the same excellent mechanical properties and uniformity of structure as in the case of performing cold working after hot working in the conventional method can be achieved. A titanium alloy material with excellent properties is manufactured.

In addition, the titanium alloy material according to the present invention (2) has 0.0% oxygen.
It may be contained up to 3% or less, thereby further increasing the strength of the alloy material.

The present invention will be explained in detail below.

First, the titanium alloy material to be manufactured in the present invention has a V:1
4 to 16 wt%, Cr: 2.5 to 3.5 wt%,
Sn: 2.5~3.5wt%, Ajl: 2.5~
It consists of 3.5 wt%, the balance Ti and unavoidable impurities, and a material for hot working is obtained by forging or blooming an ingot produced in a vacuum arc furnace or the like.

The alloy material can also contain up to 0.3% oxygen. Although it is possible to avoid increasing the strength of the present alloy material by adding oxygen, if it exceeds 0.3%, the cold workability (cold formability) will deteriorate significantly. That is, solution treatment (800℃
x 20 min → water cooling), if the oxygen content is 0.3% or less, it is possible to form a close contact surface, but if it exceeds 0.3%, breakage is observed even at the bending radius R = iot, making it practically unapplicable. .

When hot working this material for hot working, processing is started after heating it to a temperature of 900° C. or more and 1050° C. or less in a batch furnace or continuous furnace. As mentioned above, one medium-sized point of the present invention is to increase the heating temperature of the material for hot processing by it, +TiTi.

This alloy material is usually used after being subjected to solution treatment and aging treatment after the hot working process, but the structure tends to become non-uniform during the aging treatment, which reduces the mechanical properties of this alloy material. This leads to deterioration of hook and mechanical properties. This is due to non-uniformity of aging precipitation behavior, and the main cause is simply the segregation of added elements.

Conventionally, ■hot processing, ■solution treatment, ■cold processing, ■solution treatment, and ■aging treatment are used to produce the final product. The final product is homogenized by repeating the solution treatment (kneading recrystallization process) twice (total of 2 times) after processing.

On the other hand, the present invention aims to homogenize the added elements and the structure by controlling the heating temperature of wood for hot processing in a fixed and blind manner, that is, at 900°C or higher in the β change wet region. 1
By heating the material for hot working to a temperature of 050° C. or lower, the added elements can be diffused and homogenized.

Here, the upper limit of the heating temperature of the material for hot processing is 1050°C.
The reason for this is that if the heating temperature exceeds this, β
This is because grain growth becomes significant, resulting in coarsening and non-uniformity of the β grains in the Itlf product, resulting in a decrease in mechanical properties.

In addition, the lower limit of the heating temperature for hot processing materials was set at 900°C because heating below this temperature would result in insufficient uniform diffusion of the added elements, resulting in non-uniformity of the mechanical properties and structure of the final product. This is because, along with this, the mechanical properties themselves deteriorate.

In addition, the present invention aims at recrystallizing β crystals by starting rolling after heating the material for hot processing in upper dryness conditioning and performing processing in a recrystallization region of 900 ° C. or higher. It is also possible to further homogenize the added elements through recrystallization.

Next, the present invention provides a material for hot working heated to a temperature range as described above, at a processing rate of 50% or more at a temperature of at least the β transformation point or higher and 900°C or lower, and of which a processing rate of at least 850° C.
Hot working is applied at a working rate of 30% or more at a temperature below 0.degree. C., and the working is completed at a temperature above the β transformation point.

One important point of the present invention is to strictly control the processing steps in this way.

In the conventional method, C applies a stress T↑ to the processed material in the cold rolling process following the hot rolling process, and then homogenizes and refines the zero product through recrystallization behavior in the subsequent solution heat treatment process. The aim is to homogenize the additive elements, and to improve the mechanical properties during aging.

The present invention changes this idea and provides the same effect as cold processing by controlling the processing rate in the low humidity region of hot processing, and specifies the specific processing regulations as described above. This is because it is necessary to control the processing rate at 900° C. or lower, which is the non-recrystallization temperature range, in order to refine the β grains and improve the mechanical properties of the final product. In addition, processing and finishing including temperature
The reason for specifying the degree of deformation to be above the β-transformation point is that if the finishing temperature is lower than this, precipitation of one product will occur unevenly in the deformation zone formed by the J during hot working. This is because the effect of preventing precipitation in one product due to accelerated cooling in the next step is lost.

Only when the processing rate is at least 50% J at a temperature above the β transformation point and below 900°C, and at least 30% at a temperature above the β transformation point and below 850°C, a uniform rolling deformation structure will be obtained after hot rolling. The solution-treated structure and solution-treated structure also become uniform and fine. The result is an improvement in the mechanical properties and uniformity of these heat treated materials. That is, when the working rate is small, non-uniform recrystallization and recovery structure occur in the solution heat treatment after hot rolling, and as a result, aging precipitation in the subsequent aging heat treatment becomes non-uniform.

Next, the hot-worked workpiece as described above is
2℃/from the temperature above the transformation point to the temperature below 400℃
Cool at a cold TA rate of 3eC or higher. One of the features of the present invention is to perform hot working reaccelerated cooling fJl in this manner.

The β-transformation point of this alloy is 730°C, and if the cooling start temperature and cooling rate after hot working are inappropriate, a single product may precipitate unevenly in the deformation zone formed by hot working. arise,
Traces of this precipitated α-crystal are present in the next step, solution treatment II! It remains even after aging treatment and is one of the causes of uneven structure and mechanical properties and deterioration of mechanical properties.

The present invention employs accelerated cooling after hot working to prevent 0-product precipitation during air cooling after hot working.

The reason why the cooling start temperature was defined as the temperature above the β change point was because
If the cooling start temperature is below the β transformation point, non-uniform 0-product precipitation will occur in the deformation zone formed in the previous process between the end of processing and the start of cooling, and the effect of accelerated cooling to prevent α-product precipitation will be reduced. Because it will be lost.

The reason why the cooling rate was specified as 2°C/sec or more is that if the cooling rate is less than this, one product will precipitate during cooling u1, and the reason why the cooling stop temperature is specified as 400°C or less is because
This is because if cooling is stopped above this temperature, one product will be precipitated during the air cooling process to room temperature after cooling is stopped.

[Example] Next, examples of the present invention will be shown.

(2) Table 1 shows the chemical composition (wt%) of the sample material, and the diameter of the Ti-15V-3Cr-3Sn 3Δ9 alloy ingot is 550 m.

Table 1 ■, After heating the ingot of the above ingredients to 1050°C,
Forged to a thickness of 10 (1) to obtain a hot working material, and subjected to various hot working T conditions and cold 7JI.
They were processed under various conditions and their mechanical properties were investigated.

The results are shown in Table 2.

In addition, the hot working was performed by precipitating a test piece from the above-mentioned hot working material, heating the Ti to a temperature range of 00°C to 815°C, and then carrying out the finishing temperature in a temperature range of 800°C to 740°C. There were two types of finished plate thickness: 25 m and 15 mm.

The solution treatment conditions after hot working are 800℃ x 20m1n
→Water cooling and aging treatment conditions (480°C x 14hr)
-+ Air cooling (STAI), 510'Cx 1/Ihr →
Two conditions were set: air cooling (ST△2). In addition, some materials
Regarding Table 2 Chuan24), for comparison, after hot processing,
I tried solution treatment and cold working (5% in the L direction).

■The mechanical properties of each processed material in Table 2 are: board thickness 7 rtrttr from the center of board thickness, parallel part 12.5 inches, Q, l
−, 50m plate-shaped tensile test piece in the L direction under processing conditions U.
- This is data obtained by collecting 10 samples. Further, the β grain size in the same table was determined by measuring the β grain size in the LZ (thickness section parallel to the rolling direction) using a line segment method for each processing condition.

■As is clear from Table 2, the material for hot processing is 9 (
Processing is started after heating to a temperature of 10°C or higher (150'C or lower), and the processing rate is 50 at least at the β transformation point or higher and 900° or lower.
% or more, and among these, the processing rate is 30% or more at a temperature above the β transformation point and below 850°C, and then the fijl processed material is cooled at a rate of 2'C/sec or more from a temperature above the β transformation point to below 400°C. If it is cold UNI, only in case (to 1 to 14), ST△1 is strong 1 135Kg f / tsta
2 or more, elongation 5% or more, S T A 2 T: Strong D 1
The eroded strength and elongation values of 30 to 9 r/mm2 or more and elongation of 5% or more have been obtained. In addition, the standard deviation of the intensity is 1.3 or less, and the variation is small.

These mechanical f'J trades are shown in Table 2, Table 2.
The mechanical PU quality is equivalent to that of the material produced by the conventional method, which includes cold-working culms after milling. In addition, if processing conditions such as λJL, heating strip f1 in the hot-worked culm, processing rate, finishing temperature, and cold force) are made outside the provisions of the present invention, it is possible to balance both the strength and ductility. (It is impossible to do so, and there is a large variation in strength.

[Effect of the invention] According to the present invention explained above, 'Ti-15V-
In the production of 3Cr-3Sn-3A, l1 alloy material,
In particular, the material for hot working of this alloy was processed by strictly controlling the heating temperature and processing conditions. The excellent effect of being able to manufacture this type of titanium alloy material having .

Claims (2)

[Claims] (1) V: 14-16wt%, Cr: 2.5-3.5w
t%, Sn: 2.5-3.5wt%, Al: 2.5-3
．． In producing a titanium alloy material consisting of 5wt%, balance Ti and unavoidable impurities, 900% of the material for hot processing was used.
Processing is started after heating to a temperature of 1050°C or higher, at least the β transformation point or higher and 900°C or lower, with a processing rate of 50% or more,
And the processing rate is 30% above the β transformation point and below 850℃
A titanium alloy with excellent strength and ductility characterized by applying the above processing and subsequently cooling the processed material from a temperature above the β transformation point to a temperature below 400°C at a cooling rate of 2°C/sec or more. Method of manufacturing wood. (2) The method for producing a titanium alloy material according to claim 1, wherein the titanium alloy material contains 0.3% or less of oxygen.