JPS5916666A - Joining method of steel material - Google Patents

Abstract

PURPOSE:To prevent the generation of brittle layers and to improve the joint strength of steel materials by forming copper films on the surfaces of the steel materials and joining the steel materials by interposing phosphor copper solder between the joint parts of the films on said materials. CONSTITUTION:Copper is coated to about 50mu thickness by cladding or the like on the joint surfaces of steel material 9, 10. Phosphorus copper solder 13 is interposed between the coated materials 9 and 10, and the assembly is heated and brazed in a vacuum vessel or the like. Since the reaction of iron is suppressed by the phosphorus in the phosphorus copper solder by the above-mentioned method, the brittle layer consisting of the compd. of phosphorus and iron is not formed and the joint strength is increased. The method is adapted to joining of steel materials used for the tubes, fins, tanks, side plates, etc. of heat

Description

[Detailed description of the invention] Regarding the law.

Conventionally, the tubes, fins,
Brazing is generally used as a means of joining copper plates such as tanks, and tin-lead solder, phosphor copper solder, and silver solder are usually used, but since silver solder is a cylinder type, phosphor copper solder is not used. It is common to use

Also, due to strength issues, iron plates or steel plates are conveniently used for the side plates of heat exchangers, so only the parts that contact the steel plates are
A brazing filler metal other than phosphor brazing is used.

However, since the heat exchanger is integrally brazed in an inert atmosphere or in a vacuum furnace, it is not preferable to use different brazing materials due to problems such as differences in melting point and workability.

However, using 9 phosphorus copper solder on steel plates as in the case of copper plates is because the 9 phosphorus in iron and phosphorous steel reacts to form a very brittle compound (iron phosphide). , not practical. Furthermore, silver solder is expensive, resulting in high costs.

The present invention is a steel material (SS) that can prevent the formation of a brittle layer of iron phosphide or the like even when phosphorous brazing is used.

The present invention aims to provide a joining method for steel materials (including SPC and SUS i), which enables integral brazing of steel plates with phosphor brazing in a furnace, particularly in the manufacture of heat exchangers and the like.

Hereinafter, the present invention will be explained in detail based on the drawings.

This is an automobile heat exchanger shown in Fig. 1 (1) (l''1.
) upper tank (3) and core (2) attached to the top of the
It consists of a lower tank (4) attached to the lower part of the tank.

The core (2) is formed by arranging meandering fins (6) between a large number of vertically arranged tubes (5), and the sides of the rectangular shape are formed by side plates ( 7), and a bracket (8) is fixed to each side plate (7).

These tubes (5), fins (6) and tubes (5)
) and the upper and lower tanks (3) and (4) are each integrally brazed with phosphor copper solder in an inert atmosphere or in a vacuum furnace.

Next, the method of bonding force between the materials of the heat exchanger (1) will be explained in detail using a test piece of an overlap joint shown in FIG. 2 as an example.

(9) and (10) are steel materials to be joined such as tubes, fins, tanks, side plates, etc. The joining surfaces of these steel materials (9) and (10) are coated with phosphor copper brazing material (B, Cu) as a brazing material.

P) W to prevent formation of a brittle layer by reacting with phosphorus
(11) (+2'l is integrally formed.

The coatings (11) and (12) are made of copper (Cu)i and are coated on steel (IJ) (10) by a cladding method to a thickness of approximately 50 μm.

Between these steel materials (9) (1 (1), phosphor brazing (13)
Brazing was performed by heating in a vacuum furnace at 700 to 900 C for 1 to 20 minutes. The dimensions of the test piece in this case were 23 mm thick, 25 mm wide, 100 mm long, and the joint length 10 mm. As a result of the tensile shear test, the bonding strength was 78% or more, which indicates a relationship with peel strength compared to the strength required for a radiator of 3% (in the case of soldering). It peels off easily, and the strength increases as the thickness increases above 20μ. The experimental values are shown in the table below.

The reason why such a result was obtained is estimated as follows. In normal brazing, 9% copper solder is an alloy of phosphorus and copper (-Togin), and the deoxidizing effect of phosphorus removes oxides on the bottom surface, making brazing possible.

However, when a copper film is formed on the surface of steel and then brazed with phosphorous copper solder, the phosphorus CP in the phosphorous copper solder suppresses the reaction of iron (Fe), resulting in a compound of phosphorus and iron, i.e. No brittle layer is formed and the strength is increased.

This assumption is supported by the micrograph (100x magnification) of the cross section of the joint shown in FIG. That is, the fourth
In the case of joining steel materials that do not form a copper coating, as shown in Figure (al), it is observed that a band-shaped iron phosphide layer is formed between the upper and lower steel materials and the brazing filler metal in the center.

However, in the joining of steel materials having copper coatings in FIG. 4 (bl), no iron phosphide layer is formed between the brazing material and the steel materials.

In the above embodiments, cladding was used as a means for forming a copper coating on the steel material, but vapor deposition (ion blating) may be used instead. Film thickness 20
Since these methods are not practical when the temperature exceeds μ, methods such as dipping and thermal spraying may be used.

In addition, when brazing, torch brazing with flux, vacuum and atmosphere (N, H,) brazing may be used, and even if brazing in the atmosphere (including high frequency brazing) is performed, the above-mentioned Similar to the example, high bonding strength can be maintained.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a heat exchanger as an example to which the bonding force method of the present invention is applied; Fig. 2 is an enlarged sectional view of a joint of steel materials for explaining the present invention; Fig. 3 is an enlarged sectional view of a joint of steel materials. , Correlation Diagram of Peel Strength with Copper Coating Thickness, FIGS. 4(a) and 4(b) are photographs showing enlarged cross-sections of the brazed portions of steel, respectively. (1) Heat exchanger (2) Core (3) (4) Tank (5) Tube (6) Fin (7) Side plate (9) (10) Steel material (11) L12) Coating 08) Phosphorus brazing 343-

Claims (1)

[Claims] A step of forming a copper coating on the surface of the steel material in order to prevent the formation of a brittle layer made of iron phosphide by reacting with the iron of the steel material, a step of interposing a phosphorous copper solder between the joints of the steel material coating, A joining strength method for steel materials, which is characterized by the process of melting the steel and brazing the steel materials together.