JPH0638996B2 - Copper brazing filler metal for vacuum brazing of stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention mainly relates to a copper brazing material for vacuum brazing for joining stainless steel sheets to each other.

[Prior art and its problems]

Conventionally, a pure copper brazing material has been used to join the elements of the laminated heat exchanger to each other, such as an oil cooler made of a stainless steel plate. That is, 99.9% or more of Cu was deposited on the surface of the stainless steel plate as a copper brazing material for vacuum brazing. Then, as an example, a pair of intermediate shaped stainless steel molding plates as shown in FIG. 1 are fitted to each other to form one element, and an inner fin is provided inside the element. At the same time, a plurality of elements thus formed are laminated via a spacer, and they are integrally brazed and fixed in a vacuum furnace. However, it was found that a large number of voids are generated in the brazed portion when the stainless steel plates are joined together using such a pure copper brazing material. Therefore, the brazing part may leak. This is probably due to the following reasons. That is, it is considered that during brazing, Fe, Cr, Ni or the like of stainless steel diffuses into the copper brazing material, and it becomes a nucleus to draw Cu around it.

[Object and Structure of Invention]

Therefore, the present invention aims to provide a copper brazing material for vacuum brazing, in which various stainless steel sheets are firmly bonded together and the bonding part has a uniform structure without voids by various experiments. It is as follows.

That is, the present copper brazing material has a weight ratio of Fe2 to 3.3% and Ni0.4.
~ 1.0%, Cr1 ~ 1.5%, Al0.1 ~ 0.3%, Si0.03 ~
0.1% and the rest consist of unavoidable components and Cu.

[Experimental example]

In this experiment, the following copper brazing materials were used. That is, as shown in FIG. 3, 16 kinds of Fe having different values from 1.6% to 4.7% and 16 kinds of Ni having 0.2% to 1.0% are used.
9 kinds of Cr, 0.3% to 1.5% of Cr, 0.04% of Al
12 kinds of 0.32%, 4 kinds of Si 0.03% to 0.12%
A total of 20 different copper brazing materials were prepared with the proper combination of seeds. Then, as shown in FIG. 1, an element made of a stainless-steel molded plate having an intermediate shape was overlaid, and the brazing material was melted in a vacuum furnace to obtain a brazing structure shown in FIG. Then, cross as shown in Figure 2,
In the figure, the structure of each brazing material was observed with a microscope at the position of point Q.

〔Experimental result〕

In FIG. 3, 20 kinds of copper brazing materials having different components were detected, and microscopic structures almost classified into A to D as shown in the uppermost row were detected. These micrographs are shown in Fig. 4 (A) to (E), respectively.
The representative ones are shown in each. As is clear from FIG. 4, the largest voids are generated in (A) and (C).
As a result of a pressure resistance test performed on the elements having A and C, it was found that leakage often occurred from the brazed portion. Further, in FIG. 4 (E), the structure of the brazed portion was formed almost uniformly, and almost no voids existed. In the structure (E), no leakage occurred from the brazed portion in the pressure resistance test.
Also, (B) and (D) have a smaller amount of voids than (A) and (C). However (B) and (D)
As a result of the pressure resistance test, even in the brazed part, there was a case where leakage occurred extremely rarely.

As a result, it was found that the copper brazing material having the structure (E) was most preferable. The composition ratio of Fe2 is Fe2 by weight.
3.3%, Ni 0.4-1.0%, Cr 1-1.5%, Al 0.1-0.3
%, Si 0.03 to 0.1%, with the balance consisting of inevitable components and Cu.

The reason why it is better to previously include Fe, Ni, etc. in the copper brazing material is considered to be for the following reason.
That is, if Fe and Ni are already present in the copper brazing material, it seems that Fe and Ni in the stainless steel are prevented from diffusing into the copper brazing material. In order to maintain the effect of this suppression, Fe, Ni, etc. are required to some extent or more, but when they are more than necessary, on the contrary, Fe or Ni already present in the copper brazing material
It is considered that Cu is attracted to the surroundings to form voids due to the above.

〔The invention's effect〕

The copper brazing material of the present invention has a weight ratio of Fe2 to 3.3%, Ni0.4 to
1.0%, Cr1 to 1.5%, Al0.1 to 0.3%, Si0.03 to 0.
The balance is 1% and the balance consists of inevitable components and Cu.

Therefore, as is clear from the experiment, in the brazing material having the composition ratio range of the present invention, the brazing portion has a uniform structure without voids as shown in the photograph E. Therefore, there is an effect that liquid leakage does not occur from the brazed portion and a strong joint structure can be formed.

[Brief description of drawings]

FIG. 1 is an assembled perspective view showing an embodiment of a heat exchanger element in which the present copper brazing material is used, and FIG. 2 is a cross-sectional view of a main part of the heat exchanger element joined by the copper brazing material of the present invention. FIG. 3 illustrates the judgment of the quality of the copper brazing material having various component ratios by an experiment. 4 (A) to 4 (E) are representative examples of micrographs showing the grain structure of the copper brazing material of each of the judgments A to E in FIG. 1 ... Brazing material, 2 ... Stainless steel plate

Claims (1)

[Claims] 1. By weight ratio, Fe2 to 3.3%, Ni0.4 to 1.0%
Cr 1 to 1.5%, Al 0.1 to 0.3%, Si 0.03 to 0.1% A copper brazing material for vacuum brazing of stainless steel with the balance being Cu and inevitable components.