JPS61217564A - Wire drawing method for niti alloy - Google Patents

Abstract

PURPOSE:To prevent damage on wiredrawn surface, to improve efficiency by improving the rate of wire drawing per operation and to make improvement in the shape of products, by previously carrying out continuous warm wire drawing at a prescribed temp. in an open air atmosphere in subjecting an NiTi alloy to cold wire drawing with allowing an oxide film to remain on it. CONSTITUTION:The NiTi alloy consisting of 49-52at% Ni and the balance Ti or the NiTi alloy containing, as a part of the above Ni or Ti, <=4at%, in total, or >=1 kind among Fe, Cr, Mn, Co, Cu, Al, etc., is subjected to wire drawing. For example, a wire rod 1 with about 2mm diameter made by subjecting the surface of said NiTi alloy to bright treatment by pickling is first prepared, which is passed through a high-speed heating electric furnace 2 with the open air atmosphere held at a prescribed temp. and, directly after heating to 300-700 deg.C, the wire rod 1 is subjected to warm wire drawing through a wire drawing die 3. The wire rod 1 is held again at 300-700 deg.C in a furnace 2' and is then subjected to warm wire drawing through a die 4 and cooled, which is fed to dies 5-7 to be subjected to cold wire drawing, followed by rolling round a reel 8.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for drawing a NiTi alloy, particularly a method for drawing a NiTi alloy.
This paper relates to a wire drawing method that uses a tool to obtain a wire rod with excellent plastic deformation performance.

[Conventional technology] Cold die drawing is usually performed in the drawing process of NiTi alloy wire, but this material has a high work hardening and is easily seized by the die, so it is difficult to obtain a large drawing rate per drawing. Therefore, it is necessary to perform many intermediate annealing operations. As an improvement on the cold wire drawing method, for example, Japanese Patent Laid-Open No. 60-9865 discloses a wire drawing method in which an oxide film remains.

[Problems to be Solved by the Invention] However, in the above-mentioned wire drawing method, cold wire drawing and intermediate annealing are repeated, so damage to the skin due to oxidation during each intermediate annealing cannot be avoided. The expansion/contraction rate cannot be increased and the efficiency is not necessarily good. Furthermore, since the strain during wire drawing is not sufficiently removed, strong cold working continues.
There is also the possibility that the shape of the final product may be adversely affected.

The present invention solves the problems of the prior art described above, namely, prevention of damage to the wire drawing skin, improvement of efficiency by increasing the drawing rate per drawing, improvement of the product shape, and in particular, the plasticity of the drawn wire due to the mold and tool. This improves deformation performance.

[Means for solving the problems 1 In order to solve the above problems, the present invention provides Ni49-52a
t% and the remainder is Ti, or a part of the Ni or Ti is replaced with Fe, Cr, Mn
, Go, Cu, AI, etc. A method for wire drawing an NlTt alloy containing a total of 48 t% or less of one or more elements from the group consisting of Go, Cu, AI, etc. The tensile strength of the alloy is increased to 100 to 180 k (1
There is a method for drawing a Ni Ti alloy, which is characterized by adjusting the wire to /11. In other words, according to the present invention, the wire drawing process is carried out continuously at a warm temperature, thereby increasing efficiency without requiring intermediate annealing, and the oxide film produced by warm heating is compressed by a die immediately after oxidation, resulting in a dense and smooth wire drawing process. It forms a smooth surface, does not deposit a rough oxide film even after a single hour of warm heating, exhibits extremely good lubricity for the next stage die, remains an excellent lubricating film, and has good properties with no wire distortion. Wire rods can be obtained. However, after warm wire drawing, the tensile strength is approximately 90 kmMmm', and for example, when a coil spring is fed into a continuous spring forming machine that continuously forms the wire, buckling may occur due to stress applied to the die. This causes unevenness in coil diameter and pitch, and in some cases, it may be impossible to coil. In order to obtain a good product shape when forming a continuous coil spring, a tensile strength of at least 100k (1/ll1m2) is required, and if it exceeds 180k (1/mm2), coiling becomes difficult.For this reason, in the present invention, In order to increase the tensile strength, hot wire drawing is followed by strong cold drawing.
During this cold wire drawing and coiling forming,
The dense and smooth oxide film produced by warm wire drawing exhibits better lubricity than the oxide film deposited by intermediate annealing.
It has the effect of improving wire drawability and coil forming performance.

[Example 1] Hereinafter, the present invention will be explained according to examples.

FIG. 1 is a schematic diagram showing the steps of an embodiment of the present invention. A wire rod 1 having a diameter of 2 nua was prepared, the surface of which was made of 150 at% N and 50 at% Ti and brightly treated by pickling. Next, the wire is heated to 500°C by passing through a high-speed heating electric furnace 2 in an air atmosphere maintained at 500°C.
Draw the wire rod. Then, after being re-held at 500°C in the furnace 2-, warm wire drawing was performed using a die 4 (diameter 1.16n+m), and then the final stage die 52. A cooled wire rod was supplied to the wire rod, and after being cold-worked into a wire rod having a diameter of 0.77 mm, the wire rod was wound up by a winding reel 8. The tensile strength at this time is 156kO/
11m2, the thickness of the dense and smooth oxide film is 1.1μ
Met.

When cold drawing from 2mm to 0.77mm in diameter, 1
The wire drawing rate is at most 24% at most, and it takes three drawings and three intermediate annealings to pass through the die 4 of this example and reach the annealed material of 1.16 mm. The efficiency improvement with lines is obvious.

[Example 2] A wire rod with a diameter of 0.77+nm and a tensile strength of 85+M+++n+2, which was manufactured only by warm wire drawing which is a part of the process of the present invention, was molded into a coil spring with an outer diameter of 71Ill using an automatic coil spring forming machine. However, it was impossible to form the wire due to buckling. On the other hand, the wire rod with a diameter of 0.77 mm and a tensile strength of 156 kg/llll112 manufactured in Example 1 can be formed into a tight coil spring with an outer diameter of 71IIIl without any lubrication without any problems, and the dimensional tolerances should be sufficiently satisfied. there were.

In addition, the tensile strength is 158k manufactured using the normal cold wire drawing process.
(The 1/mm2 wire with a diameter of 0.77 mm could be formed into a tight coil spring with an outer diameter of 7i+m without any particular problems.
Feeder feeding required lubrication.

It can be seen that the wire rod spring forming die according to the present invention has excellent cold forming performance.

[Effects of the Invention] As described above, according to the present invention, an NtTi alloy wire having excellent plastic workability can be efficiently obtained.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the invention. 1: Supply wire rod 2.2-: Electric furnace 3.4: Warm wire drawing die 5.6.7: Cold wire drawing die 8: Winding machine Figure/Figure

Claims (1)

[Claims] N containing 49 to 52 at% of Ni, the balance being Ti
iTi alloy or part of the Ni or Ti is replaced with Fe, C
A total of 4at of one or more elements from the group consisting of r, Mn, Co, Cu, Al, etc.
A method for wire drawing a NiTi alloy containing 300 to 700% of hot-rolled wire in an air atmosphere.
The tensile strength of the alloy is adjusted to 100 to 180 kg/mm^2 by continuous warm wire drawing at a temperature of ℃ and then cold wire drawing without removing the attached oxide film. A method for drawing a NiTi alloy, characterized by: