JPH05287473A - Manufacture of silver thin sheet - Google Patents

Abstract

PURPOSE:To provide the method for manufacturing a silver thin sheet used as an electrical contact material or the like. CONSTITUTION:A silver ingot constituted of 20 to 100ppm Cu, and the balance Ag with inevitable impurities is prepd. This silver ingot is subjected to cold rolling to manufacture a silver thin sheet. At this time, the silver ingot or silver sheet in the process of the cold rolling is heated to 550 to 900 deg.C. The heated silver ingot or silver sheet is cooled by water. In particular, the draft in the cold rolling is preferably regulated to 50 to 95%. Even if the silver thin sheet immediately after the manufacture or after being allowed to stand for a long term is exposed to a high temp. of about >=2800 deg.C, the coarsening of the crystalline grains in the silver thin sheet is hard to generate. Thus, by using this silver thin sheet, the effects that cracks on the silver thin sheet are difficult to generate and roughening on its surface is hard to generate even if being exposed to a high temp. are given. Furthermore, the effects that the softening of the silver thin sheet is difficult to generate and the deterioration in its quality is small even if being allowed to stand for a long term after the manufacture are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin silver plate used as an electrical contact material or other electrical material.

[0002]

2. Description of the Related Art Conventionally, a silver thin plate used for an electrical contact or the like has been manufactured by the following manufacturing method. That is, Ag10
0% by weight, or Cu 0.002-0.01% by weight (Cu20-100ppm) and prepare the ingot consisting of the balance Ag, after chamfering this ingot, subjected to a warm rolling process at a temperature of about 300 ℃, Thickness about 4 mm
Get about a silver plate. Then, this silver plate is subjected to cold rolling, and if necessary, subjected to intermediate annealing at a temperature of about 150 to 200 ° C. during cold rolling to obtain a silver thin plate with a thickness of about 0.3 to 0.7 mm. .. If more is needed, 200
The final annealing is performed at ~ 300 ° C to adjust the strength and crystal grain size of the thin silver plate.

This thin silver plate was formed into a certain shape, and was sometimes exposed to a high temperature of 800 ° C. or higher when it was subsequently used as an electric material or when it was joined to another material. Then, at this high temperature, cracks may occur in the silver thin plate. In addition, the surface of the thin silver plate may be roughened. In particular, when a silver thin plate with a rolling rate of 50% or more during cold rolling is adopted, and this silver thin plate is left at room temperature for one week or more and then exposed to a high temperature of 800 ° C or more, the above-mentioned silver thin plate is The cracks were marked.

[0004]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention As a result of investigations by the present inventors on the reasons why a thin silver plate is cracked or the surface thereof is roughened, the crystal grains in the thin silver plate are found to be exposed at a high temperature. It turned out to be coarse. That is, it has been found that the coarsening of the crystal grains in the silver thin plate reduces the strength of the silver thin plate or roughens the surface of the silver thin plate. Also, if a silver thin plate with a rolling ratio of 50% or more is left at room temperature for one week or more, the silver thin plate will soften with time, and if such a silver thin plate is used and exposed to high temperatures, the crystal The grains are likely to be coarsened, the strength of the silver thin plate is further reduced, or the surface of the silver thin plate is significantly roughened.

Therefore, the present inventor has conducted various studies on the composition and manufacturing method of the silver thin plate in order to suppress the coarsening of the crystal grains in the silver thin plate. As a result, the present inventor, during cold rolling which is a manufacturing process of a silver thin plate, when performing intermediate annealing at a relatively high temperature, it is difficult for the crystal grains in the silver thin plate to coarsen even after being exposed to a high temperature later. And proposed an invention according to Japanese Patent Application No. 3-292092.

[0006] After that, as a result of the research conducted by the present inventor, not only the intermediate annealing was performed at a relatively high temperature but also the silver plate heated at a high temperature was rapidly cooled, so that a relatively large amount of Cu was contained in Ag. To form a fine and uniform crystal structure, and the recrystallization temperature rises. Even when the obtained silver sheet is exposed to high temperature, the crystal grains in the silver sheet become coarse. The inventors have found that it is difficult and that the silver sheet is not softened with time even if it is left at room temperature for one week or more, and the present invention has been accomplished.

[0007]

[Means for Solving the Problems] That is, the present invention provides Cu20-
A silver ingot consisting of 100 ppm, the balance Ag and unavoidable impurities, is subjected to cold rolling to produce a silver thin plate, wherein the silver ingot or the silver plate in the middle of cold rolling is heated to 550 to 900 ° C., and thereafter. The present invention relates to a method for producing a silver thin plate, which comprises cooling the heated ingot or the silver plate with water.

In the present invention, first, a silver ingot having a predetermined elemental composition is prepared. That is, a silver ingot containing 20 to 100 ppm of Cu is prepared. If the Cu content is less than 20 ppm or exceeds 100 ppm, the crystal grains in the ingot are likely to be coarsened, and the crystal grains of the obtained silver thin plate are also coarsened, which is not preferable. Further, if Cu exceeds 100 ppm, the silver ingot is hardened and the cold rolling property is deteriorated, which is not preferable. Such a silver ingot, by dissolving a predetermined amount of Cu and Ag, after degassing,
It can be easily obtained by continuous casting with a water-cooled mold or casting with a die.

The silver ingot thus prepared is repeatedly subjected to cold rolling to obtain a silver thin plate having a predetermined thickness (generally 0.3 to 0.7 mm). What is important in the present invention is heating at a temperature of 550 to 900 ° C. That is, the silver ingot is heated to 550 to 900 ° C.
Moreover, it is to heat the silver plate during cold rolling to 550 to 900 ° C. Then, the silver ingot or the silver plate heated to 550 to 900 ° C. is cooled with water. By cooling with water, the silver ingot or silver plate is cooled rapidly, that is, at a high cooling rate. Due to the high temperature heating and the rapid cooling, Cu is relatively solid-dissolved in Ag. This is because, for example, when a heated silver ingot or a silver plate is left to stand in the air and cooled, the cooling rate is slow and Cu does not form a solid solution in Ag in a large amount. The silver thin plate obtained as a result has a relatively low recrystallization temperature, and tends to soften with time if left for one week or more. When such a thin silver plate is exposed to a high temperature, the crystal grains are coarsened, causing cracks and surface roughening. On the other hand, in the present invention, since Cu is a solid solution in a relatively large amount in Ag, the recrystallization temperature becomes relatively high, and even if the obtained silver thin plate is left for one week or more, It does not tend to soften over time. Further, since the solid solution amount of Cu is large, it is difficult for crystal grains to grow, and it becomes fine and uniform. Therefore, the silver thin plate obtained by the method according to the present invention, even when exposed to a high temperature, the crystal grains are not easily coarsened, and cracking and surface roughening hardly occur.

The manufacturing method according to the present invention, in particular,
It is preferably 50 to 95% and applied when cold-rolled to obtain a silver thin plate. The reason for this is that when the rolling ratio is set to 50 to 95%, the obtained silver thin plate is likely to soften with time. When the rolling ratio is set to 50 to 95% and the method according to the present invention is applied, the obtained silver thin plate is difficult to soften with time, and after leaving it for one week or more, the crystal grains are coarse even when exposed to high temperature. It is difficult to form, and cracks and surface roughness are less likely to occur. Here, the rolling ratio is 100 × [(thickness of silver ingot or silver plate before cold rolling)-(thickness of thin silver plate)] / [silver ingot or silver plate before cold rolling] Thickness].

The thin silver plate obtained as described above is used for electric materials such as electric contacts. At this time, the thin silver plate is formed into a predetermined shape, then exposed to high temperature and subjected to various treatments.

[0012]

【Example】

Examples 1 to 4 and Comparative Examples 1 to 4 Using a silver ingot having a purity of 99.99% by weight and a master alloy of Ag-Cu, a Cu content shown in Table 1 was compounded in a graphite crucible. And dissolved. After degassing, continuous casting with a water-cooled mold and casting with a die having a different preheating temperature were carried out, followed by chamfering to obtain a silver ingot. The dimensions of this ingot are 30 mm thick, 150 mm wide, and 2 mm long.
It was 50 mm. This silver ingot was cold-rolled to obtain a silver thin plate. At this time, during the cold rolling, when the silver plate had the thickness shown in Table 1, it was heated in the heating furnace at the temperature shown in Table 1 for 3 hours. After heating, it was cooled by the method shown in Table 1. The water cooling in Table 1 indicates that the heated silver plate was immersed in a water bath for cooling, the air cooling indicates that it was left in the atmosphere for cooling, and the furnace cooling means that the heat source of the heating furnace was turned off. It shows that it was cooled in the furnace. Then, after cooling, cold rolling was performed to obtain a desired thickness.

[0013]

[Table 1]

The silver thin plate obtained as described above is heated to 20 ° C.
The following tests were carried out in order to evaluate the performance when left for one day or under 50 days. That is, a thin silver plate was introduced into an atmospheric furnace preheated to 900 ° C,
Hold for a time and then remove. Then, the size of the crystal grain was measured. The crystal grain size was measured by the following method. That is, the silver thin plate is observed with an optical microscope to measure the area of crystal grains. Considering a circle having the same area as this area, the diameter of this circle was defined as the size of the crystal grain. It is generally said that when the size of the crystal grains in the thin silver plate exceeds 100 μm, cracking and surface roughening occur when exposed to high temperatures. Therefore, when the crystal grains are 100 μm or less, the evaluation of cracks etc.
When the crystal grains exceeded 100 μm, the evaluation of cracks was rated as x. Further, in order to evaluate the change with time of softening of the silver thin plate, the Vickers hardness of the silver thin plate after standing for one day and the Vickers hardness after standing for 50 days were measured and compared. Those with a hardness difference of less than 10 were evaluated as ◯, and those with a hardness difference of 10 or more were evaluated as x. Then, as a comprehensive evaluation, those having all the above evaluations of ◯ were comprehensively evaluated as ◯, and those having × included in the above evaluations were comprehensively evaluated as x. The results are shown in Table 2.

[0015]

[Table 2]

As is clear from the results shown in Table 2, Example 1
Even if the silver thin plate obtained by the method according to 4 is exposed to a high temperature of 900 ° C. for 1 hour, the crystal grain size is 100 μm in any case.
The size of the crystal grains when the silver thin plates obtained by the methods according to Comparative Examples 1 to 4 are treated in the same manner is more than 100 μm immediately after obtaining the silver thin plates or after 50 days have passed. Was over 100 μm. Therefore, Examples 1 to 1
It can be seen that when the silver thin plate obtained by the method according to No. 4 is used, the silver thin plate is unlikely to be cracked or surface roughened even when exposed to a high temperature. Further, the silver thin plates obtained by the methods according to Examples 1 to 4 have a smaller degree of softening occurring over time than the silver thin plates obtained by the methods according to Comparative Examples 1 to 4. Therefore,
It can be seen that the silver thin plates obtained by the methods according to Examples 1 to 4 are less likely to deteriorate in quality even if left for a long period of time.

[0017]

As described above, the silver thin plate obtained by the method according to the present invention is less likely to undergo coarsening of crystal grains even when heated to a high temperature of about 800 ° C. Also, this silver thin plate is not easily softened even if left for a long period of time, and coarsening of crystal grains and deterioration of its quality hardly occur. Therefore, using this thin silver plate, or using a thin silver plate that has been left for a long period of time, in order to bond it to other materials or to use it as an electrical material, a high temperature of about 800 ° C or higher is used. Even if exposed to, it is hard to generate coarse crystal grains in the thin silver plate. Therefore, the silver thin plate maintains high strength, and even if a physical impact is applied, it is difficult for the thin silver plate to be cracked and the surface thereof is not roughened. Further, as described above, the silver thin plate obtained by the method according to the present invention also has an effect that its quality is less likely to deteriorate.

Claims (2)

[Claims] 1. A method for producing a silver thin plate by cold rolling an ingot of silver consisting of 20 to 100 ppm of Cu, the balance Ag and inevitable impurities, wherein the silver ingot or the silver plate in the middle of cold rolling is 55
A method for producing a silver thin plate, which comprises heating to 0 to 900 ° C., and then cooling the heated silver ingot or silver plate with water. 2. The method for producing a silver sheet according to claim 1, wherein the rolling ratio in cold rolling is 50 to 95%.