JPH08141702A - Method for producing Ni-Ti alloy having excellent workability - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing a Ni-Ti alloy having excellent workability. [Structure] A Ni-Ti alloy melt is cast by quenching and consists of fine equiaxed crystals with a grain size of 50 μm or less.
A method for producing a Ni-Ti alloy having the above elongation, wherein the Ni-Ti alloy melt has a depth d of 3 to 3 in the mold.
It is poured into a 5 mm mold and quenched and cast. [Effect] A Ni—Ti based alloy having a fine equiaxed crystal structure 1 with excellent workability can be easily manufactured, and the manufacturing process can be significantly shortened to improve the productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a Ni-based material having excellent workability.
The present invention relates to a method for manufacturing a Ti-based alloy.

[0002]

2. Description of the Related Art Ni-Ti alloys have characteristics such as shape memory and superelasticity, and are excellent in corrosion resistance and biocompatibility, and are suitable for air outlets of air conditioners, pressure control valves of rice cookers,
Widely used in orthodontic wires, brassieres wires, and eyeglass frames. By the way, the Ni-Ti alloy is manufactured by the following method. First, Ni-T
The i-based alloy is melted, and this molten metal is used in a mold to have a diameter of several cm
Cast into a large ingot of cm. As shown in FIG. 3, the structure of this ingot is composed of columnar crystals 2 grown from the surface toward the inside, and coarse equiaxed crystals 3 finally solidified at the central portion. Such an ingot structure has poor workability. Therefore, hot forging is performed to change to a tough forged structure, and then hot rolling and cold rolling are sequentially performed to form a thin plate or a thin wire. Since the Ni-Ti alloy has a large work hardening, it is necessary to perform intermediate annealing a number of times during cold rolling, resulting in poor productivity and high cost.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
A method has been proposed in which a small ingot having a shape close to that of a product is obtained by a small continuous casting method such as a single roll method, a twin roll method, and a melt spinning method, and the cold working step is shortened. However, in the small continuous casting method, the molten metal is solidified in sequence from the surface of the mold such as a rotating roll, so that the obtained ingot structure is entirely composed of columnar crystals 2 as shown in FIG. : Single roll method,
Fig. 4B: Twin roll method), and all were inferior in workability. Also, the small continuous casting equipment was expensive. In addition, powder molding methods such as a powder metallurgy method, a combustion synthesis method, and a method of performing a thermal diffusion reaction after molding a mixed powder of Ni and Ti have been proposed. However, in these methods, the powder is expensive, it is necessary to remove the remaining fine pores by an expensive hot isostatic press, and the performance is deteriorated due to the inclusion of an oxide film on the powder surface. There was a cost or performance problem. The present inventor has conducted various studies on a method for producing a Ni-Ti alloy, and has found that a fine equiaxed crystal structure is excellent in workability, and that the equiaxed crystal structure can be obtained by casting in a thin mold. Then
After further research, the present invention has been completed. An object of the present invention is to provide a method for producing a Ni-Ti alloy having excellent workability with high productivity and low cost.

[0004]

According to the first aspect of the present invention,
The Ni-Ti alloy melt is cast by quenching and the crystal grain size is 50μ.
A method for producing a Ni-Ti based alloy, which is composed of fine equiaxed crystals of m or less and has an elongation of 20% or more in the cold, comprising:
A method for producing a Ni-Ti alloy having excellent workability, characterized by pouring a molten Ti-based alloy into a mold having a depth d of 3 to 5 mm in the mold and performing rapid casting.

According to a second aspect of the present invention, the Ni-Ti-based alloy contains Ni in an amount of 49 to 52 at%, and the balance is Ti and inevitable impurities, or Ni or Ti of the Ni-Ti alloy. Part of Fe, Cr, Al, V, P
The Ni-having excellent workability according to claim 1, wherein the Ni-Ti-based alloy is one or more of d, Mn, Co, Nb, and Cu, and is a Ni-Ti-based alloy substituted in the range of 0.01 to 2 at%. T
This is a method for producing an i-based alloy.

[0006]

Next, the technical contents of the invention according to claim 1 or 2 will be described. In claim 1, the mechanism of forming a fine equiaxed crystal structure is considered as follows. That is, the molten metal injected into the mold does not solidify until pouring is completed and is maintained in a liquid state, and solidification starts after the pouring is completed. At the start of solidification, supercooling progresses throughout the melt, and a large number of crystal nuclei are generated everywhere in the melt. Therefore, as shown in the schematic diagram of FIG. 1, the obtained ingot has a fine equiaxed crystal structure 1 with a grain size of 50 μm or less.
become.

The Ni-Ti alloy produced by the present invention is
The ingot structure consists of a fine equiaxed crystal structure with excellent workability and a crystal grain size of 50 μm or less, and the ingot elongation is 20% in the cold.
That is all. Here, the measurement of elongation in the cold shall be performed under the conditions of a gauge length of 50 mm and a tensile speed of 50 mm / min., By cutting out a test piece from the ingot while leaving the ingot surface in the thickness direction. . The fine equiaxed crystal structure having a crystal grain size of 50 μm or less is formed by casting a molten Ni—Ti alloy into a mold having excellent thermal conductivity. 200 for mold material
A metal material having a thermal conductivity of 0.1 cal / cm · sec. · ° C. or higher is suitable, and usually a copper material, an iron material or the like is used.

The mold used in the present invention is, for example, a vertically divided split mold as shown in FIG. In the present invention, the reason why the depth d in the mold is limited to 3 to 5 mm is that when the depth d exceeds 5 mm, the mold wall surface before the entire molten metal injected into the mold is in a supercooled state. This is because the solidification progresses from the center toward the center to form columnar crystals and the workability deteriorates. When the depth d in the mold is less than 3 mm, the cooling rate of the molten metal becomes fast, solidification progresses before the molten metal fills the mold, and fine equiaxed crystals cannot be obtained, and the molten metal is insufficiently supplied. This is because casting defects such as solidification shrinkage holes occur.

The ingot obtained according to the invention of claim 1 has a fine equiaxed crystal structure which is thin and has a large elongation and is excellent in cold workability, and has no defects and is of high quality Ni-Ti.
A system alloy is obtained. Further, in order to obtain a Ni-Ti alloy having a predetermined shape, the number of times of annealing in cold working can be reduced and the productivity is improved.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples. (Example 1) A Ni-Ti alloy containing 50.85 at% Ni and the balance Ti and unavoidable impurities was vacuum melted in a high-frequency melting furnace into a molten metal, and this molten metal was used as a split mold made of copper shown in FIG. To obtain a Ni—Ti alloy ingot. The depth d in the copper mold was changed in the range of 3 to 5 mm. The inner width t of the copper mold is 100 mm, the thickness u of the mold wall is 30 mm, and the height h is
It was 200 mm.

(Example 2) A Ni-Ti alloy ingot was obtained by the same method as in Example 1 except that an iron mold was used instead of the copper mold.

(Example 3) Ni was added to the Ni-Ti alloy.
A Ni—Ti based alloy ingot was obtained by the same method as in Example 1 except that a Ni—Ti based alloy containing 50.60 at% and Cr at 0.2 at% and the balance Ti and unavoidable impurities was used.

(Comparative Example 1) A Ni-Ti alloy ingot was obtained by the same method as in Example 1 except that a copper mold having an inner mold depth d of 2 mm, 7 mm, or 10 mm was used.

A part of the obtained ingot was subjected to a tensile test to examine the elongation before breaking. The elongation was measured by cutting a test piece from the ingot with the surface of the ingot in the thickness direction left, and performing the measurement under cold conditions with a gauge length of 50 mm and a pulling speed of 50 mm / min.
The width of the test piece was the same as the thickness. The remaining ingot has a reduction rate of 30
% Cold rolling was performed. No intermediate annealing was performed during cold rolling. The number and depth of edge cracks of the obtained cold rolled material were measured. Edge crack is about 20 sheets of each plate,
The number and crack depth were measured. The number of edge cracks was the number of rolled material per 1 cm in length, and the depth was the average of all the observed crack depths. The results are shown in Table 1.

[0015]

[Table 1]

As is clear from Table 1, in Examples 1 to 3 (No. 1 to 7) of the present invention, the ingot structure is composed of a fine equiaxed crystal structure, and the elongation is large and the workability is excellent. The number of edge cracks in the plate material decreased. The copper mold (No. 2) had slightly higher elongation than the iron mold (No. 4), the number of edge cracks was small, and the crack depth was shallow. This is considered to be due to the difference in thermal conductivity. On the other hand, in Comparative Examples Nos. 8, 9 and 11, since the in-mold depth d exceeded 5 mm, columnar crystals were formed in all of them, elongation was reduced, edge cracks were increased in number, and depth was increased. It became deep. In No. 10, since the depth d was less than 3 mm, solidification progressed during pouring and defects due to insufficient hot water occurred.

The case where two kinds of plate-shaped Ni-Ti alloys are manufactured by using a copper or iron mold has been described above, but according to the present invention, a metal mold made of another material is used. The same effect can be obtained when producing a Ni—Ti alloy having a composition other than the plate shape and having another composition.

[0018]

As described above, according to the present invention, it is possible to easily manufacture a Ni-Ti alloy having a fine equiaxed crystal structure that is excellent in workability, and it is possible to greatly shorten the manufacturing process and to improve productivity. Is improved, and a remarkable effect is industrially achieved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an aspect of a structure of a Ni—Ti based alloy produced by the method of the present invention.

FIG. 2 is a perspective view showing an aspect of a mold used in the method of the present invention.

FIG. 3 Ni produced by a single roll method or a twin roll method
It is a schematic diagram of the structure of-Ti type alloy.

FIG. 4 is a vertical cross-sectional view of the structure of a Ni—Ti based alloy manufactured by a conventional method.

[Explanation of symbols]

 1-Fine equiaxed crystal structure 2-Columnar crystal 3-Coarse equiaxed structure

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location // C22K 1:00 (72) Inventor Kenichi Katahira 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Kawa Electric Industry Co., Ltd.

Claims (2)

[Claims] 1. A quenching casting of a Ni-Ti alloy melt,
Cold, consisting of fine equiaxed crystals with a grain size of 50 μm or less
A method for producing a Ni-Ti alloy having an elongation of 20% or more, characterized by injecting the molten Ni-Ti alloy into a mold having a depth d of 3 to 5 mm in the mold and performing rapid casting. And a method for producing a Ni-Ti alloy having excellent workability. 2. The Ni-Ti alloy contains 49 to 52 Ni.
Ni-T containing at% and balance Ti and unavoidable impurities
i alloy, or a part of Ni or Ti of the Ni-Ti alloy is replaced with Fe, Cr, Al, V, Pd, Mn, Co, Nb,
It is any one of Ni or two or more kinds of Cu and is a Ni-Ti based alloy substituted within the range of 0.01 to 2 at%.
A method for producing a Ni-Ti alloy having excellent workability as described.