JPS61253354A - Manufacture of alpha+beta type titanium alloy sheet - Google Patents

Abstract

PURPOSE:To produce Ti alloy rolled sheet having uniform structure and superior mechanical property, by rolling alpha+beta type Ti alloy while regulating conditions of primary rolling, reheating and secondary rolling. CONSTITUTION:Slab of alpha+beta type Ti alloy is heated to temp. of (alpha+beta) two phases range by bath furnace or continuous furnace, and rolled primarily by >=30% draft of total draft at the temp. range. Next, the rolled material is reheated from <=500 deg.C surface temp. of the material after completing primary rolling to (alpha+beta) two phases range temp. of (beta transformation point -200 deg.C)-beta transformation point, held at the temp. for >=30min then rolled by >=30% draft to hot rolled sheet having a desired size. The titled sheet having structure superior in uniformity and improved mechanical property can be produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an α+β type titanium alloy plate, and is capable of economically producing an α+β type titanium alloy plate with excellent mechanical properties and uniform structure. The purpose is to provide a method.

[Conventional technology]

Titanium alloy materials have excellent properties such as light weight, high strength, and high corrosion resistance, so they are mainly used as aircraft body materials.

This titanium alloy is roughly classified into α type, α+β type, and β type, and the present invention aims to provide a novel method for producing α+β type titanium alloy.

By the way, titanium alloy material is one of the female processed materials, and improvement of the uniformity of the structure and improvement of mechanical properties (especially improvement of elongation) have been issues, and various thick plate rolling and hot rolling methods are being investigated. being done.

The present inventors have demonstrated that the so-called two-heat rolling method, in which heating and rolling are repeated at temperatures in the α+β two-phase region, is effective in improving the uniformity and mechanical properties of hot-rolled α+β titanium alloy hot-rolled materials. I found this out and have already proposed it.

However, in this two-heat rolling method, heating of the secondary rolled slab is done by reheating the secondary rolled material that has been air-cooled to room temperature, which has the disadvantage of increasing rolling costs.

[Summary of the invention]

The present invention was made to improve the above-mentioned conventional drawbacks, and aims to provide a rolling method that is highly economical without impairing the excellent material properties provided by the two-heat rolling method.

As a result of various studies, the inventors of the present invention found that by controlling the secondary rolling conditions, reheating conditions, and secondary rolling conditions, an α-deca-base titanium alloy plate with excellent economic efficiency and material properties was manufactured. I found out that it can be done. In other words, by controlling the reduction ratio of the primary rolling, which was not controlled in the past, together with the reheating holding temperature and time, it is possible to hot charge the secondary rolled slab without deteriorating the material properties, and the energy consumption is reduced. This makes it possible to improve both time and economic efficiency.

The purpose of the primary rolling in the two-heat rolling method is to homogenize the structure by eliminating coarse grain boundary α crystals that precipitate in a network form at old grain boundaries that existed in the slab stage through recrystallization accompanied by diffusion. In other words, α in −th rolling l
By processing in the +β non-recrystallization temperature range, recrystallization progresses during heating of the secondary rolling slab due to strain energy, the network-like coarse grain boundary α crystals disappear, and the structure becomes uniform. Since secondary rolling is performed using the slab having this uniform structure as a raw material, the structure of the secondary rolled material is made uniform and the mechanical properties are improved. Therefore, heating of the secondary rolled slab has the purpose of promoting recrystallization, so when performing hot charging, it is necessary to strictly control the reduction rate of the primary rolling and the reheating temperature and time to complete the recrystallization. This makes it possible to obtain uniformity of the structure and good mechanical properties.

In the present invention, first the α+β+2 Cutitaph slab is heated to a temperature in the α+- two-phase region, and the total reduction rate is 3 in this temperature region.
The primary rolling is completed by applying a rolling reduction of 0.04 or more. This titanium alloy slab is heated using a batch furnace or a continuous furnace.

The reason why the heating temperature is defined as the temperature in the α+β two-phase region is as follows. In other words, when heating to a high temperature in the β region, β
This is because network-like coarse grain boundary d-crystals are precipitated at the prior β grain boundaries as the temperature is slowly cooled to a temperature near the β2α+β transformation point during cooling from the range temperature, and the microstructure uniformity of the final rolled material is greatly reduced. . Further, the reduction in processing at the temperature in the α+β two-phase region is specified to be 30 coefficients or higher because the structure cannot be made uniform in the reheating process of the secondary rolling slab if the total reduction ratio is lower than this.

- After the next rolling, reheating is performed and secondary rolling is performed.
00°C) to a temperature in the α+− two-phase region of the β transformation point,
After maintaining this temperature range for 30 minutes or more, reduction is applied at a total reduction ratio of 3096 or more at a temperature in the α+β two-phase range to obtain a hot rolled plate of a predetermined size. This reheating is performed using a batch furnace or a continuous furnace.

Here, the reason why the reheating start temperature is set to 500℃ or higher is that although there is no restriction on the reheating start temperature due to the material, it is economical if the slab surface temperature is set to 500℃. This is because the amount decreases.

The reason why the reheating temperature was set in the α+β two-phase region from (β transformation point −200°C) to β transformation point is as follows.

In other words, in the present invention, during the reheating process of the secondary rolled slab at a temperature in the a+β range, recrystallization proceeds based on the strain energy in the material stored in the primary rolling, and the structure becomes uniform. This effect does not occur at temperatures below the β transformation point -200°C; on the other hand, when heated to a high β region temperature, cooling from the β region temperature results in slow cooling again to a temperature near the β = α + β transformation point. This is because network-like coarse grain boundary α crystals precipitate at the old grain boundaries, and the effect of homogenizing the structure is lost.

The reason why the temperature is held in the above temperature range for 30 minutes or more is because if the holding time is less than 30 minutes, the progress of recrystallization during reheating will not be sufficient, resulting in a decrease in the uniformity of the structure after secondary rolling. .

Furthermore, the working rate at temperatures in the α+- two-phase region was limited to 30 degrees or more for the total rolling reduction because the structure would not be made uniform during the heat treatment process of the rolled plate if the total rolling reduction was less than this.

〔Example〕

Ti-64AA-4%V alloy, which is a typical α+β type titanium alloy shown in the composition list in Table 1 (β transformation point is 1000°C
) 550m ingot was heated to 120mm after heating to 1050mm
A slab was created by hot forging to a certain thickness. After heating this slab to 1050-700℃, 900-60G
Primary and secondary hot rolling was carried out in the temperature range of 36°C.
Finished in a thick rolled plate. Heat treated material (955°OX1.
5 hr-4W, Q, + Is 38°OX 6 h
The mechanical properties of r 4 A, C,) are parallel to the center of the plate thickness.

A 35 m tensile test piece was taken in the t direction and adjusted. Here, the heat treatment was performed on a test piece of 125 nmt x 100wW x 1λsmt. Further, the macroscopic non-uniformity of the structure of the α+β type titanium alloy poses a problem. Therefore, the uniformity of the structure is determined by the average grain size (average of 30 grains) of α crystals in the LZ plane of the heat-treated material.
was measured at 100 locations and evaluated by comparing the standard deviations under each rolling condition.

Table 2 shows heating and reheating conditions and primary and secondary rolling conditions. Furthermore, the mechanical properties of the steel plate obtained thereby are shown in the same table.

When the primary and secondary rolling conditions defined in the present invention are satisfied, it is recognized that the mechanical properties (especially ductility) and microstructure uniformity after hot rolling are significantly improved. However, in the case of rolling conditions that satisfy only one of the secondary and secondary rolling conditions, sufficient mechanical properties and structural uniformity are not obtained. In addition, if sufficient heating and holding time is required for secondary rolling,
Even if we changed the conventional method of starting reheating of the primary rolled material from room temperature and adopted a method of reheating the secondary rolling material from a high temperature and performing secondary rolling, no deterioration of mechanical properties or structure was observed. do not have.

Although a Ti-6%At-4%V alloy was used as an example of the present invention, Ti-6 which is an α+β type titanium alloy
Similar effects were confirmed by applying the present invention to titanium alloy bases such as 4kL-6'1V-218n, and the present invention is applicable to all α+β type titanium alloys. Furthermore, although the present invention was discovered in the production of hot-rolled plates, even if a round bar or the like is produced by hot rolling or forging as a hot working process using bloom or billet as the raw material,
As long as the hot working conditions of the present invention are adhered to, it is possible to produce a product with excellent uniformity of structure and improved mechanical properties, similar to the hot rolled sheet E.

Procedural amendment (voluntary) January 7, 1985 Mr. Michibu Uga, Commissioner of the Patent Office (Mr. Patent Office Examiner)
1. Indication of the case Showa bO year patent application No. 956; 2
Z No. 2, Name of the invention, Me + β momme titanium metal, Mori, made by Mr. Shi 4, Agent.
1a5, date of amendment order 6, amendment subject to amendment Contents 1 Correct "1050~" to Ir5so-J at the end of line 15 on page 7 in the specification of the present application.

2. In the same book, page 8, line 11, the words ``steel plate'' are corrected to ``titanium alloy plate.''

3. In the 9th page, line 14 of the circular, the phrase ``make to original size'' is corrected to ``observe''.

Claims (1)

[Claims] An α+β type titanium alloy slab is heated to a temperature in the α+β two-phase region, and primary rolling is performed with a total reduction rate of 30% or less in this temperature range, so that the surface temperature after rolling is 500°C or more. After reheating from (β transformation point -200°C) to a temperature of β transformation point and holding in this temperature range for 30 minutes or more, perform secondary rolling at a temperature in the α + β two-phase region with a total reduction of 30% or more. A method for manufacturing an α+β type titanium alloy plate characterized by the following.