JPS60234956A - Manufacture of titanium alloy plate - Google Patents

Abstract

PURPOSE:To manufacture a Ti alloy plate having a uniform structure and superior mechanical properties and causing no surface cracking by forging or rolling an alpha+beta Ti alloy ingot at a temp. in the alpha+beta2 phase range at a specified total draft, reheating the resulting slab, and hot rolling it. CONSTITUTION:The alpha+beta Ti alloy ingot is forged or rolled at a temp. in the alpha+beta2 phase range at >=30% total draft to form the slab. The resulting slab is reheated and hot rolled to obtain the Ti alloy plate. It is preferable that the slab is reheated to the temp. in the alpha+beta2 phase range and hot rolled at >=30% total draft.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a titanium alloy plate. [Prior Art and its Problems] Conventionally, when manufacturing an α+β type titanium alloy sheet metal, an ingot was forged or Large, wide slabs that are bloomed and rolled are used.
When manufacturing this slab, processing is performed in the β region where deformation resistance is low. Titanium alloy plates obtained by further hot-rolling such slabs generally have problems such as extremely poor structural uniformity and mechanical properties (particularly elongation),9 and the tendency to crack on the surface. ing.

[ [Structure of the invention] In the α+β type titanium alloy plate manufacturing process, a slab is made from an ingot by forging or blooming rolling, and this slab is further hot rolled or the plate that has undergone such a processing process has a structure. It is β that causes deterioration of uniformity and mechanical properties more than the above.
The slabs produced in the
By slowly cooling the temperature near the β transformation point, the old β
This is because coarse grain boundary α crystals precipitate in a network shape at the grain boundaries, and some of them remain without disappearing even after hot rolling and subsequent heat treatment. Although no method has been adopted to control the processing conditions at the slab manufacturing stage by focusing on the material and structure of the slab, the present inventors have determined that the slab manufacturing conditions and the structure and material of the obtained titanium alloy plate are As a result of examining the relationship between I found out.

In other words, in order to eliminate the network-like coarse grain boundary α crystals precipitated in the slab manufacturing stage, it is necessary to perform C crystallization accompanied by diffusion in a furnace, and by intense processing at the temperature of the α + β two phase castle described above, strain energy is applied to the slab. It was found that the strain energy accumulated during the subsequent hot rolling promoted recrystallization, thereby making the structure uniform.

Therefore, the present invention provides α+β type titanium alloy ingots.
A cis slab is produced by forging or rolling at a total reduction rate of 30 or more at a temperature in the two-phase region, and this slab is hot rolled after reheating.

Further, according to further studies by the present inventors, hot rolling is carried out under processing conditions of strong reduction at a temperature in the α+β2 phase region, and furthermore, in the slab manufacturing process before hot rolling, the α+β2 phase region as described above is produced. It has been found that a more uniform structure can be obtained after heat treatment of a hot-rolled plate by performing heavy working at a temperature of Either the slab has been processed and strain energy has been accumulated, or it is heated to a temperature in the α + β two phase region, which is the temperature at which network-like coarse grain boundary α crystals do not precipitate, to cause recrystallization and equalize the structure in a furnace. After that, strain energy is accumulated by further hot rolling at a temperature in the α+pg phase region, and this strain energy promotes recrystallization in the next heat treatment process, making the structure more uniform. It depends on what you do. Therefore, in the second invention of the present application, an α+β type titanium alloy ingot is forged or rolled at a total reduction rate of 3091 or more at a temperature in the α+β 2 phase region to form a cis slab, and the cough slab is made into a cis slab in the α+β 2 phase region. temperature [4 After heating, total reduction rate 30176
This is how hot rolling is performed. α + β type titanium alloy has poor hot workability at temperatures in the α + β two phase region, and therefore, when applying heavy working in the α + β temperature range, if a slab in which network-like coarse grain boundaries a & remain remains, this network However, in the above invention, hot rolling is performed using a slab in which the network-like grain boundary coarse α crystals have disappeared, so the surface cracks may occur frequently. It is possible to prevent cracking and to produce a hot-rolled plate with excellent surface properties.The manufacturing conditions of the present invention will be specifically explained below.

In the present invention #'i, first, an α+β type titanium alloy ingot is heated to a temperature of β transformation point −200°0 or higher and β transformation point +100°0 or lower, and then continuously heated without being forcedly cooled in the middle. It is formed into a slab of a predetermined size by forging at a temperature in the α+β two-phase region or by applying processing at a total reduction rate of 30 inches or more using a blooming press. A batch furnace or a continuous furnace is used to heat the titanium alloy ingot. The heating temperature was limited as above for the following reason: 0, i.e., β transformation point -200° At heating temperature of 0, the hot workability of the α+β type titanium alloy decreases significantly, and surface cracks occur. Rolling becomes difficult due to increased hot deformation resistance. On the other hand, the heating temperature is p transformation point +1
If the temperature exceeds 00°0, the surface of the titanium alloy ingot will be significantly oxidized, causing increased scale loss and surface flaws during rolling.・The total rolling reduction rate in the above temperature range must be 30 mm or more. However, when the Fi is less than 30%, the strain energy accumulated is insufficient, and a sufficient effect of homogenizing the structure in the subsequent hot rolling process cannot be obtained. The slab manufactured under such processing conditions is cooled, reheated, and hot rolled to manufacture a titanium finish plate.

Alternatively, the hot rolling conditions of the present invention are to heat the slab produced according to the processing conditions described above to a temperature in the α+β2 phase region, apply a reduction with a total reduction of 30 inches or more at a temperature in the α+β2 phase region, and then reduce the dimensions in places. A batch furnace or continuous furnace is used to heat the titanium alloy slab to be rolled into a hot rolled plate. The reason why the heating temperature was defined as α+β2 phase temperature is as follows. That is, in the present invention, recrystallization progresses based on the strain energy in the material stored in the slab manufacturing process during the heating process of the slab at the temperature in the α + β two phase region, and the structure becomes uniform.
When heating to a temperature in the β region, which is higher than the α + β region, cooling from the β region temperature is gradually cooled to a temperature near the τβ2α + β transformation point.
This is because crystals may precipitate and the effect of homogenizing the structure of the slab according to the present invention may be lost.
If the total reduction rate of working at a temperature in the phase range is less than 30 inches, the effect of homogenizing the structure as expected in the heat treatment process of a rolled plate cannot be obtained.

〔Example〕

Ti-6% At-4% alloy ingot (diameter 550 m
) is heated to 1050'O to perform blooming rolling, and the resulting slab is subsequently hot rolled to a temperature of 950 to 800'
Finished into a pressure plate with a thickness of 36 mm in the temperature range of 0°C, and further heat treated (955°OX
hr 4W, Q, + 538°c X 6 hr
-+ A-C-) The mechanical properties of the heat-treated materials were investigated.

The results are shown in Table 2 together with the manufacturing conditions.

The mechanical properties of the rolled material and the heat-treated material were investigated by taking test specimens from parallel parts 61w1y, a, taa■ in the t direction to the center of the plate thickness.
The test was carried out using a test piece of 12.15 m” x 12.15 t.Furthermore,
Macroscopic non-uniformity is a problem with the structure of α+β type titanium alloys, so the uniformity of the structure is determined by adjusting the average grain size of α crystals (average of aO grains) in the LZ plane of STA material to 1 of that of heat-treated material.
The results were evaluated by measuring at 00 locations and comparing the standard deviation of the average grain size under each rolling condition. (a) and (b) are respectively Table 2 Chuin 1 material (comparison material) and Yang 6 material (invention material)
This is an enlarged microscopic photograph (100x) of the tissue.

According to Table 2 and Figures 1 and 2 above, the rolling reduction ratio at a temperature in the α+β2 phase region that satisfies the rolling conditions of the slab of the present invention and is the manufacturing condition of the slab of the present invention is 30%. It can be seen that in the above cases, the mechanical properties (especially ductility) after hot rolling are significantly improved. Looking at the standard deviation of the average grain size, when the rolling reduction at the temperature in the α+β2 phase region is 30 inches or more, the standard deviation of the average grain size after hot rolling heat treatment is small and the structure is homogenized. Furthermore, the slab manufactured by the manufacturing method of the present invention has excellent resistance to surface cracking during rolling, and therefore, the α+β type titanium alloy plate obtained thereby can suppress surface cracking and have excellent surface properties. It can be seen that

Note that the present invention is not limited to the alloys of the above embodiments, but is also applicable to Ti alloys, for example.
Other α+ such as 6%At'6%V-2%Sn alloy
Needless to say, it is applicable to all β-type Ti alloys.

Furthermore, the basic principle of the present invention can also be applied to the production of round bars by hot rolling or forging using bloom or billet as the raw material; Product 1 with excellent structural uniformity and improved mechanical properties, just like in inter-rolled sheets! i- can be obtained.

〔Effect of the invention〕

According to the present invention described above, it is possible to appropriately manufacture a titanium alloy plate having a uniform structure and mechanical properties such as elongation, and having no surface cracks, etc., which is an excellent industrial effect. .

[Brief explanation of drawings]

Figures 1 (a) and (b) are enlarged micrographs of the microstructure of material 1 in Table 2. (a) shows the as-rolled material and (b) shows the heat-treated material. (a) and (r+) are enlarged micrographs of the structure of the Nh6 material in Table 2, where (a) is the as-rolled material and (b) is the heat-treated material. Patent applicant Nippon Steel Tube Co., Ltd. Nippon Kogyo Co., Ltd. Inventor Chibu Ouchi Suedo Nagahiro Budo Hide Yama Hide Daido Sawamura - Bema Hanaki Oio Representative Patent attorney Sho Yoshihara Tamaya Dou Takahashi Consumption Bentenshi Hiroshi Yoshihara Children 1 Figure (No, I STA11

Claims (2)

[Claims] (1) Form a cis slab by forging or rolling an α+β type titanium alloy ingot at a temperature in the α+β two-phase region with a total reduction of 30 mm or more, and then hot-roll the slab after reheating. Characteristic manufacturing method of titanium alloy plate. (2) The α+β type titanium alloy ingot is made into a cis slab by rolling or rolling it at a temperature in the α+β2 phase region at a total reduction rate of 30 mm or more, and after heating the slab to a temperature in the α+β2 phase region, the entire A method for producing a titanium alloy plate characterized by hot regularization at a rolling reduction rate of 30 inches or more.