JPH08117802A - NiTi alloy wire manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a method for producing a NiTi-based alloy wire rod which is less likely to cause surface cracking and can be put into practical use relatively easily. [Structure] When a NiTi-based alloy material is thin-wire processed to a wire diameter of 3 mm or less, the material is heated to a softening point of 500 to 800 ° C. or higher and swaged to a wire diameter of 2 mm or less. As a processing method up to a predetermined size, the conventional rolling processing by a roll, wire drawing processing by a die, or a combination thereof is applied. By swaging the NiTi alloy, impact due to rolling is applied over the entire surface, the wire is processed almost uniformly, and at the same time, the metal crystal grains of the surface layer are refined to increase the wire strength, Scratches due to surface cracks and wrinkles are less likely to occur.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a NiTi alloy wire having superelasticity or shape memory characteristics.

[0002]

2. Description of the Related Art This NiTi alloy wire rod is disclosed in
-161753, JP-A-59-28548 and JP-A-60-9865, the cross-sectional shape is rectangular or square by the rolling method, forging method and wire drawing method using a die. It is processed and manufactured into ribbons and circular round wires.

[0003]

However, these processing methods tend to cause cracks on the surface of the material due to the weak tensile strength and bending strength, which are the drawbacks of the NiTi alloy itself, and the subsequent steps. However, there is a problem that the defect is expanded and the product yield is reduced, and the application of wire drawing by the wire drawing method at the stage where the wire diameter is large requires a large drawing force, and the processing equipment is relatively large in size, and it is put into practical use. Has the drawback of being difficult.

The present invention eliminates the large drawing force and the generation of flaws in the NiTi-based alloy wire rod processing method. The surface crack is less likely to occur, and the NiTi-based alloy can be put into practical use relatively easily. It is an object of the present invention to provide a method for manufacturing a wire rod.

[0005]

The present invention has achieved its object by applying a swaging method.
When processing a thin wire of i-based alloy to a wire diameter of 3 mm or less, the material is heated to a softening point or higher and swaging is applied to a wire diameter of 2 mm or less, and a processing method up to a predetermined dimension thereafter. Is characterized by applying a conventional rolling process using a roll, a wire drawing process using a die, or a combination thereof.

The NiTi-based alloy applicable in the present invention is an alloy in which Ni is 50 to 60 wt% and the balance is mainly Ti.

The condition for swaging is 50
Co to 15-25 in the atmosphere by heating to 0-800 ° C
The wire is fed while rolling a cemented carbide rolling blade containing wt%. If the Co content is less than 15% by weight, the rolling blade may become unbearable due to impact due to rolling and may be broken.
On the other hand, when it is 25 wt% or more, the rolling blade becomes soft and the deformation becomes large. Therefore, C in the cemented carbide of the rolling blade
The o content is preferably 18 to 22% by weight.

When applying swaging, if the wire diameter is 2 mm or less, the rolling force cannot be increased and the grain refining effect is reduced, so the wire diameter of the NiTi alloy wire to which swaging can be applied is the minimum wire diameter. Up to 2 mm. It is preferably up to 2.5 mm.

[0009]

[Function] The NiTi alloy is hot-rolled by a swage bar having a cemented carbide rolling blade, so that the impact due to rolling is applied over the entire surface, and the wire is processed almost uniformly. By refining the metal crystal grains of the surface layer, the strength of the wire is increased, and surface cracks and scratches due to wrinkles are less likely to occur.

[0010]

EXAMPLE An alloy material made of 56% by weight Ni-44% by weight Ti having a circular cross section with a wire diameter of 8.2 mm and a wire diameter of 2.5 was used.
Swage processing was carried out by heating at 700 ° C. in the atmosphere under the condition of an average surface reduction rate of 21% until the thickness became mm. The rolling blade at this time is a cemented carbide of 20 wt% Co-80 wt% WC. Next, under the condition of an average surface reduction rate of 24%, the wire was heated to 700 ° C. in the atmosphere and drawn by a die three times to obtain a NiTi alloy body having a wire diameter of 1.65 mm. Obtained N
The i-Ti wire exhibited a shiny black-gray surface and had the properties of superelastic and shape memory alloy wires.

The materials used in the above examples for comparison were
Under the same conditions, wire drawing was performed to a diameter of 2.5 mm by groove roll processing, but crack-like scratches due to wrinkling occurred on the wire rod surface at the end in the wire axis direction. For this reason, it is necessary to remove the scratches by cutting before finishing the final wire rod, and the yield is 2 times as compared with the swaging process.
It was more than twice as bad. Further, it was attempted to process this material by wire drawing to a wire diameter of 8.2 mm to 1.65 mm, but it was difficult because a large drawing was required at a stage where the wire diameter was large.

[0012]

According to the present invention, the following effects can be obtained.

(1) By processing with a swage bar provided with a cemented carbide rolling blade at the stage where the wire diameter is thick, no cracks in the axial direction on the surface of the wire material are generated, so that extra damage removal is required. Unnecessary steps are unnecessary.

(2) The thinning process can be easily performed, and the processing yield is improved.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B21J 5/00 B 5/06 F

Claims (1)

[Claims] 1. When a NiTi-based alloy material is used as a wire having a wire diameter of 3 mm or less, Co is contained in an amount of 15 to 25% by weight until the material is heated to a softening point or higher and the wire diameter becomes 2 mm. NiTi is characterized by applying hot rolling by a swaging machine equipped with a cemented carbide rolling blade, and rolling by a roll or wire drawing by a die up to a predetermined size thereafter. For manufacturing alloy-based wire rods.