JP4068486B2 - Electrode material for resistance welding and manufacturing method thereof - Google Patents

Description

【００３４】
【表２】

【００３５】
得られた板材の全圧延率は９５〜９７．５％で、板材中のカリウム量は、１０、５５、１０３、２００ｐｐｍであった。この板材を第１の実施の形態と同様な寿命試験を行った。その結果を下記表３に示した。
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【表３】

【００３７】
【発明の効果】
以上説明したように、本発明によれば、電極の再結晶温度を向上させることによって耐熱性が向上するだけでなく、強度や耐衝撃性も著しく向上するので、銅や銅合金等のように固有抵抗値の低い母材を溶接する場合においても、変形、クラック、欠け等の損傷が生じにくくなり、繰返し使用することができるので、生産性が向上し、製造コストが低廉になるという顕著な効果を奏する抵抗溶接用電極材料とその製造方法とを提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode material for resistance welding, and more particularly to an electrode material for resistance welding suitable for resistance welding of copper or a copper alloy.
[0002]
[Prior art]
In general, resistance welding is performed by superimposing welded materials made of metal materials, and superposing the overlapped portions with a pair of resistance welding electrodes and applying a large current of several thousand amperes while pressing them strongly. In this method, electric resistance heat generated through a current flowing through the workpieces is used as a welding heat source to weld the workpieces. In the case of this resistance welding method, the temperature of the welded portion is determined by the difference between heat generated by contact resistance and heat dissipation. The amount of heat generation is governed by the current value, the energization time, and the specific resistance of the material, and the amount of heat dissipation is governed by the volume, thermal conductivity, specific gravity, and specific maturity of the welded member.
[0003]
For this reason, it has been difficult to weld metals such as copper and copper alloys having small specific resistance and large thermal conductivity by resistance welding.
[0004]
However, in recent years, tungsten (W) and molybdenum (Mo) -based electrodes that do not react with copper, in particular, tungsten-based materials having features such as high specific resistance, excellent heat resistance, and high hardness and strength. It is known that even metals that are difficult to resistance weld such as copper can be welded relatively well.
[0005]
However, even when tungsten is welded with a metal having a low specific resistance value such as copper or copper alloy, the electrode is deformed after a few uses, for example, 500 to 600 times, or damage such as cracks and cracks. Has occurred and has become unusable. For this reason, it is necessary to frequently replace the electrode each time, resulting in poor productivity and high production costs.
[0006]
In Patent Document 1, in order to increase the durability of the electrode, an electrode material having a fibrous structure is formed from a W sintered alloy, and the end surface of the fibrous structure (RD surface: a cross section perpendicular to the rolling direction). It is disclosed that the problem can be solved by configuring a welding surface for clamping the workpiece.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-158178
[Problems to be solved by the invention]
In the case of resistance welding, although depending on welding conditions, the temperature of the welded portion instantaneously reaches a high temperature of about 1200 to 1500 ° C. Therefore, even with the electrode disclosed in the above-mentioned patent document, since the recrystallization start temperature of pure tungsten is about 1100 ° C., it had a fibrous structure with relatively high strength and excellent impact resistance in the initial stage of use. Although it was an electrode, there was a problem that the electrode was recrystallized during repeated use and changed into a coarse equiaxed grain structure and became brittle. In other words, the strength and impact resistance required for the electrode were remarkably lowered by recrystallization, and the electrode was deformed and damaged such as cracks and cracks.
[0009]
Therefore, the technical problem of the present invention is to provide a resistance welding electrode capable of further improving durability, that is, a resistance welding electrode material having high strength, high toughness and high recrystallization temperature, and a method for producing the same. .
[0010]
[Means for Solving the Problems]
As described above, in Patent Document 1, attention is paid to the directionality of the tissue constituting the electrode as described above in order to increase the durability of the electrode. That is, durability is improved by using the end surface of the fibrous structure as a weld surface.
[0011]
However, no matter how the direction of the structure is controlled, the material recrystallizes and becomes brittle during use, so the strength and impact resistance are significantly reduced, and the electrode is deformed, and damage such as cracks and chipping occurs. Remains.
[0012]
In the present invention, the recrystallization temperature of the electrode is improved in order to increase the durability of the electrode. That is, the present inventors have found that by increasing the recrystallization temperature and minimizing the structural change due to repeated use, embrittlement due to recrystallization can be suppressed, and the strength and impact resistance can be significantly improved. It has been reached.
[0013]
According to the present invention, there is provided an electrode material for resistance welding made of a tungsten alloy, the composition of which is 10 ppm or more and 200 ppm or less of potassium, the balance being tungsten and unavoidable impurities , and the metal structure of the tungsten alloy is a fibrous structure. The electrode material for resistance welding characterized by comprising is obtained.
[0014]
Further, according to the present invention, there can be obtained a resistance welding electrode material characterized in that the theoretical density ratio is 95% or more in the resistance welding electrode material .
[0015]
Further, according to the present invention, there is provided a method for producing any one of the resistance welding electrode materials, the step of mixing a tungsten powder and potassium to produce a mixed powder, and pressing the mixed powder. A step of producing a pressed body, a step of sintering the pressed body at 1800 to 2200 ° C. in a hydrogen stream, and a hot rolling of the sintered body at 1500 to 1700 ° C. The process for producing the electrode material for resistance welding is provided .
[0016]
Furthermore, according to the present invention, in the method for manufacturing a resistance welding electrode material, there is obtained a method for manufacturing a resistance welding electrode material, characterized in that the total rolling rate of the hot rolling is greater than 95%. It is done.
[0017]
In general, pure tungsten starts to recrystallize at about 1100 ° C. However, in the present invention, when the recrystallization start temperature is set to 1200 ° C. or higher, when used as a resistance welding electrode, the life, that is, the number of times of use is significantly improved. I found out that I can do it.
[0018]
In the present invention, the additive element for improving the recrystallization temperature is potassium (K), and it is desirable to reduce the amount as much as possible in consideration of the productivity of the material, the improvement of the processing yield, the ease of recycling, and the like.
[0019]
In the present invention, the K content is preferably 10 ppm or more and 200 ppm or less, and preferably 50 to 100 ppm. The reason is that if it is less than 10 ppm, the recrystallization temperature is not improved, whereas if it exceeds 200 ppm, plastic working of the material is difficult and the production yield is poor.
[0020]
In the present invention, the theoretical density ratio of the tungsten alloy is preferably 95% or more. The reason is that when it is less than 95%, even if the recrystallization temperature is 1200 ° C. or higher, the impact resistance, fracture resistance, and wear resistance are insufficient.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0022]
(First embodiment)
Various potassium-dispersed tungsten powders having an average particle size of 4 μm were prepared by a conventional method. The powder was molded at 100 to 200 MPa by cold isostatic pressing, and then sintered at 1800 to 2200 ° C. for 10 to 30 hours in a hydrogen stream to prepare a sintered body having a thickness of 50 mm.
[0023]
The obtained sintered body was hot-rolled at 1500 to 1700 ° C. to obtain a plate material having a thickness of 1 mm (total rolling rate of 98%). The amount of potassium in the plate material was 5, 10, 30, 55, 72, 103, 147, 200, 220, 250 ppm. As the amount of potassium increased, the hot rolling property decreased. A good plate material with almost no cracks was obtained up to about 100 ppm of potassium. Cracking occurred up to a potassium content of about 100 to 200 ppm, and the yield was slightly reduced, but the productivity was not hindered. When the amount of potassium exceeded 200 ppm, many cracks occurred and the yield was significantly reduced.
[0024]
The summary results are shown in Table 1 below. The theoretical density ratio of the plate material having a potassium content of 200 ppm or less was 99% or more.
[0025]
The obtained plate was heated in hydrogen at a temperature of 1000 to 2000 ° C. for 1 hour, and the structure was observed with an optical microscope to examine the recrystallization temperature (recrystallization start temperature). The results are shown in Table 1 below. The higher the amount of potassium, the higher the recrystallization temperature. When the amount of potassium was 10 ppm or more, the recrystallization start temperature increased by 100 ° C. or more than that of pure tungsten (5 ppm of potassium).
[0026]
Furthermore, a tensile test and a simple impact test were conducted to examine the tensile strength and impact resistance. Here, the tensile test is performed at a strain rate of 6.7 × 10 ⁻⁴ S ⁻¹ at room temperature and 1200 ° C. (assuming a temperature that is instantaneously applied to the material when used as an electrode material for resistance welding). It was. As a result, the tensile strength was higher as the amount of potassium was larger at both room temperature and 1200 ° C.
[0027]
The tensile strength at room temperature and 1200 ° C. of a plate material having a potassium amount of 10 ppm or more is 2.5 times or more and 1.1 times or more that of pure tungsten (5 ppm potassium amount), respectively, and the strength is remarkably increased by making the potassium amount 10 ppm or more. I was able to improve.
[0028]
On the other hand, in the simple impact test, a steel ball with a mass of 30 g is dropped freely from a height of 2 m onto a sample of a processed material and a 1200 ° C heat-treated material (assuming an initial use state and a material repeatedly used as a resistance welding electrode material, respectively). In addition, the fracture state of the sample surface was visually observed and distinguished from those without cracks (◯), with cracks (Δ), and cracks (x). The results are shown in Table 1 below.
[0029]
As shown in Table 1 below, in the case of the processed material, pure W (amount of potassium of 5 ppm) was not cracked, but cracking was confirmed. No crack was found in the material having a potassium content of 10 ppm or more. In the case of the heat treated material at 1200 ° C., cracks were slightly observed on the plate material having a potassium content of 10 ppm, but no crack was confirmed when the potassium content exceeded 10 ppm. The crack of the plate material with 10 ppm potassium is considered to be because the heat treatment temperature (1200 ° C.) is the same as the recrystallization start temperature and a part of the structure is recrystallized.
[0030]
Moreover, pure tungsten (5 ppm potassium amount) was divided. By making the potassium amount 10 ppm or more, not only the strength but also the impact resistance could be remarkably improved.
[0031]
An electrode shape (for example, a plate material having a thickness of 1 × width of 20 × length of 30 mm was produced from the plate material of Table 1 below. Five copper wires having a diameter of 0.5 mm were superposed and this pair of electrode materials (eg, 5 × 20 mm A life test was conducted by applying a predetermined current (for example, 5000 A) and pressurizing at a pressure of 5 kN, and the life was determined by electrode deformation, hooking, etc. The results are shown in Table 2 below.
[0032]
As shown in Table 2 below, in the case of pure tungsten (5 ppm potassium amount), the welding frequency was only about 600 times, but the recrystallization start temperature should be 1200 ° C. or higher (10 ppm or higher potassium amount). Thus, the number of weldings was 3500 or more, and the life was significantly increased. This is because not only room temperature characteristics (strength and impact resistance) but also heat resistance are improved by increasing the recrystallization start temperature.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
The total rolling rate of the obtained plate material was 95 to 97.5%, and the amount of potassium in the plate material was 10, 55, 103, and 200 ppm. The plate material was subjected to a life test similar to that of the first embodiment. The results are shown in Table 3 below.
[0036]
[Table 3]

[0037]
【The invention's effect】
As described above, according to the present invention, not only the heat resistance is improved by increasing the recrystallization temperature of the electrode, but also the strength and impact resistance are remarkably improved. Even when welding a base material with a low specific resistance value, damage such as deformation, cracking and chipping is less likely to occur and it can be used repeatedly, so that productivity is improved and manufacturing costs are reduced. The electrode material for resistance welding which has an effect, and its manufacturing method can be provided.

Claims (4)

An electrode material for resistance welding made of a tungsten alloy,
The composition is potassium 10 ppm or more and 200 ppm or less, and the balance consists of tungsten and inevitable impurities ,
An electrode material for resistance welding, wherein the metal structure of the tungsten alloy has a fibrous structure.   The electrode material for resistance welding according to claim 1, wherein the theoretical density ratio is 95% or more. A method for producing the resistance welding electrode material according to claim 1 or 2,
A step of mixing tungsten powder and potassium to produce a mixed powder;
A step of pressing the mixed powder to produce a pressed body;
Sintering the pressed body in a hydrogen stream at 1800-2200 ° C. to produce a sintered body;
Hot rolling the sintered body at 1500-1700 ° C. to produce a rolled material;
A method for producing an electrode material for resistance welding, comprising:   4. The method for manufacturing a resistance welding electrode material according to claim 3, wherein the total rolling reduction of the hot rolling is a process exceeding 95%.