JPH06136498A - Mirror finishing treatment for beta-type titanium alloy - Google Patents

Abstract

PURPOSE:To obtain a beta-type titanium alloy easy of working at high temp. and capable of a mirror finishing. CONSTITUTION:Thermomechanical treatment, where plastic working at a temp. in a range between (beta transformation temp. -150 deg.C) and (beta transformation temp. +50 deg.C) for improving workability and accelerating fine and uniform precipitation, successive solution heat treatment at a temp. in the range between the beta transformation temp. and (beta transformation temp. +50 deg.C), and further aging treatment for increasing strength are combined, is applied to a beta-type titanium alloy, followed by the mirror-finish polishing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mirror-finishing a β-type titanium alloy which can be easily plastically worked and has a mirror surface.

[0002]

2. Description of the Related Art A β-type titanium alloy, which is called a metastable β-type titanium alloy and which does not undergo martensite transformation by quenching and is in a β single phase at room temperature, generally has a β transformation temperature and a recrystallization temperature substantially equal to each other. Therefore, recrystallization and grain growth occur rapidly in the heat treatment above the β transformation temperature, recrystallization does not occur yet in the heat treatment below the β transformation temperature, and the α phase precipitates along the deformation zone during processing. It remains. Therefore, the conventional recrystallization treatment of β-type titanium alloy is carried out at a temperature higher than the β-transformation temperature, and the grain size of the crystal grains obtained by the treatment is about 15 μm at the most even if it is made finer ( For example, Bulletin of Faculty of Engineering, Ibaraki University, 37 (1989) 155).
Even if the β-type titanium alloy having such a structure is subjected to an aging treatment, the hardness obtained is at most about Hv400, and a mirror surface cannot be obtained. When titanium alloy is used for exterior parts of wristwatches and ornaments such as necklaces, specularity is important for expanding design variety.

[0003]

The precipitation of the α phase from the recrystallized structure of equiaxed grains by aging treatment is non-uniform because the α phase preferentially precipitates at and near the grain boundaries. With such a structure, a mirror surface cannot be obtained even by polishing. Further, it requires a long aging time, which is not preferable in practice.

In the prior art, since the solution treatment as described above is performed after cold working, in order to suppress the variation in strength depending on the location of the product, the cold treatment for precipitating a uniform and fine α phase by aging treatment is performed. As the inter-working, it was necessary to carry out the working such as rolling or extrusion which gives a relatively uniform strain distribution. Therefore, as this cold working, it is necessary to use die forging to actually form a structure or bulge forming of a thin plate because the strain distribution becomes uneven or a large elongation cannot be obtained and it cannot be formed. It was difficult to process the product.

[0005]

In order to solve the above problems, the present invention provides a β-type titanium alloy with a β transformation temperature of 150 or less.
After performing plastic working in the temperature range from ℃ to β transformation temperature or more to 50 ℃ to obtain a uniform recovery structure,
The solution treatment is performed in the temperature range of not less than the transformation temperature and 50 ° C, and the aging treatment at 400 to 550 ° C is performed to make the α phase uniform
It was made to precipitate finely. A mirror surface can be obtained by polishing the titanium alloy having such a structure.

[0006]

[Operation] When processing (hot working) of β-type titanium alloy is completed within a temperature range of 150 ° C below the β-transformation temperature to 50 ° C above the β-transformation temperature, recovery progresses during deformation, and recrystallization is driven by the processing. Strain energy, which is a force, does not accumulate so much, and even if the temperature at which the processing is completed is higher than the static recrystallization temperature, recrystallization does not occur at that temperature. That is, the recrystallization temperature rises due to the hot working. Therefore, the recovery structure can be obtained by performing the processing at a temperature equal to or lower than the recrystallization temperature which is increased by the hot working. Since this recovery structure is processed at a relatively high temperature, the strain is relatively uniform, but it is not yet sufficient, and α phase precipitation is also observed in the processing below the β transformation temperature. Therefore, uniform strain and α
Perform solution treatment for solid solution of the phases. Precipitation of α phase due to aging from the structure thus obtained is very uniform.
It becomes fine and the hardness is very high, and the variation is small.
Therefore, the titanium alloy having such a structure can be mirror-finished by polishing.

[0007]

EXAMPLES The present invention will be described in detail below with reference to examples. The test material used in the present invention is a solution-treated β-type titanium alloy having the chemical components shown in Table 1. The β transformation temperature of this test material was about 740 ° C.

[0008] (Example 1) This test material was subjected to 80% cold rolling, and a tensile test piece having a gauge length of 15 mm, a width of 7 mm and a thickness of 2 mm was cut out from the cold rolled material. Next, the following five types of samples A, B, C, D and E were prepared from these test pieces. Sample A is a tensile test piece with a temperature of 50 below the β transformation temperature.
After being held at 0 ° C. for 10 minutes, a tensile test of about 50% was performed at a deformation rate of 10 mm / min, after the test, the sample was heated and held at 750 ° C. for 10 minutes, and further aged at 450 ° C. for 24 hours. Samples B, C, D, and E are samples in which the tensile test temperature of Sample A was changed to 600, 700, 800, and 900 ° C., respectively.

[0009] After polishing these samples with sandpaper, they were buffed with alumina abrasive grains. The hardness of the sample thus obtained was measured and the specularity was evaluated. The results are shown in Table 2. Samples A and E have low hardness and poor specularity. Samples B, C, D
Had good hardness and specularity. Therefore, the plastic working temperature is set to a temperature range of 150 ° C. or less from the β transformation temperature to 50 ° C. or more from the β transformation temperature. Here, the solution treatment after high-temperature tensile deformation can be performed after cooling after high-temperature tensile deformation, or even if it is solution-treated after high-temperature tensile deformation without cooling, the same results as in Table 2 are obtained. It was Similar results were obtained even when the initial structure before heating to the tensile test temperature was not a rolled material but a material having an equiaxial structure.

Example 2 A ring with a radius R as shown in FIG. 1 was cut out from a test material and used as a blank material in FIG.
The wristwatch case was die forged as shown in. As this processing method, the blank material described above is set in a mold maintained at 750 ° C., and 0.05 to 20 mm / min.
A constant temperature forging method (superplastic forging method) for forming in one step was used at a deformation rate of. After constant temperature forging, deburring and cutting are carried out to finish the watch case, then at 750 ℃
The solution treatment was carried out for a minute, and then an aging treatment was carried out at 450 ° C. for 24 hours. After this aging treatment, mirror polishing was performed. Then, the hardness distribution of the cross section of the wristwatch case and the specularity of the surface were examined.
Fig. 3 shows the result of hardness distribution at a deformation rate of 3 mm / min.
Shown in. The hardness is almost Hv450 regardless of the measured portion, and it is understood that there is little variation in strength depending on the location.
The specularity was also good. Here, the die temperature in the forging process does not matter, and it is sufficient if the blank material is at or above the β-transformation temperature even after the process and the recrystallization is not completed after the process. That is, the present invention can be applied even to hot forging in which the mold temperature is lower than the temperature of the blank material.

In this embodiment, Ti-15V-3Cr-3 is used.
Although Sn-3Al alloy is used, it goes without saying that the present invention is a mirror-finishing method applicable to other β-type titanium alloys.

[0012]

As described above, according to the present invention,
After subjecting the β-type titanium alloy to plastic working in a temperature range of 150 ° C or lower than the β transformation temperature to 50 ° C or higher of the β transformation temperature, and subsequently performing solution treatment in a temperature range of β transformation temperature to the β transformation temperature or higher and 50 ° C or higher. A β-type titanium alloy having very good specularity can be obtained by a very simple method of aging treatment for increasing hardness. In addition, processing above the β transformation temperature shows superplastic behavior,
It also has the effect of being extremely easy to process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a blank material before processing according to the present invention.

2A is a plan view of a wristwatch case according to the present invention, FIG.
(B) is a sectional view and (c) is a side sectional view.

FIG. 3 is a hardness distribution diagram of a wristwatch case according to the present invention.

Claims (2)

[Claims] 1. A step of plastically working a β-type titanium alloy in a temperature range Tβ-150 ° C. ≦ T ≦ Tβ + 50 ° C., and a step (b) a solution treatment in a temperature range Tβ ≦ T ≦ Tβ + 50 ° C. c) A mirror surface treatment method for a β-type titanium alloy, which comprises sequentially performing an aging treatment in a temperature range of 400 ° C. ≦ T ≦ 550 ° C., and (d) performing a hot polishing treatment (Tβ is a β transformation temperature). . 2. The plastic working is hot working or isothermal working for forming a structure.
A method for mirror-finishing a β-type titanium alloy as described.