JPH0810952A - Welded composite parts and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a highly reliable welded composite parts by controlling the thickness of the chill structured layer and/or the hardened structured layer to be generated in the weld boundary part on the spheroidal graphite cast iron side to be below the prescribed value to prevent the weld crack in welding the member made of spheroidal graphite cast iron and the member made of steel using the weld metal made of stainless steel. CONSTITUTION:The thickness of the chill structured layer and/or the hardened matrix structure to be generated by the heat-affected welding boundary part on the spheroidal graphite cast iron side is <=0.7mm. Welding is achieved at the welding speed of >=2m/min using the weld metal made of austenitic stainless steel. The normal welding speed is 0.3-0.7m/min, and by increasing the speed to the value of >=2m/min, a calorie to be given to the members made of spheroidal graphite cast iron and steel during the welding is reduced and the chill structuring of the spheroidal graphite cast iron in the welding boundary part is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welded composite part in which a spheroidal graphite cast iron member and a steel member are joined by welding, and a method for producing the same.

[0002]

2. Description of the Related Art In structural members, it has been conventionally difficult to weld a spheroidal graphite cast iron member and a steel member with high reliability. Therefore, a mechanical joining method in which a flange or the like is provided at a joining portion of each member and joining is performed via a bolt and a nut is generally adopted. When welding is used, a mild steel welding material is usually used.
As described in No. 7592, a special welding method has been proposed in which an austenitic stainless welding material is used, or an iron-nickel welding material and an austenitic stainless welding material are used together.

[0003]

However, in the mechanical joining method in which a flange or the like is generally adopted, not only the number of parts such as bolts and nuts increases but also the structure of members becomes complicated, Assembly work is also complicated.

When welding is used, the assembly structure is simplified as compared with the mechanical joining method. However, the mild steel-based welding material has good weldability with steel members, but poor weldability with spheroidal graphite cast iron members, and has poor reliability in terms of joint strength, and at the same time, it has a chill structure layer at the weld boundary. The hardened matrix structure layer becomes thicker, the hardness becomes higher and brittle, and weld cracking occurs. Further, in the iron-nickel-based welding material, the welding with the spheroidal graphite cast iron member is better than the mild steel-based welding material, but it is not only inferior in strength, but also more expensive and economical than the mild steel-based welding material. Inferior. Furthermore, when using an austenitic stainless welding material, the weldability with the spheroidal graphite cast iron member is relatively good, but tends to reduce the occurrence of chill organization and weld cracking of the spheroidal graphite cast iron, The weld boundary is still unreliable.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems in the welding and joining method, and to provide a welded composite part in which a spheroidal graphite cast iron member and a steel member are welded and joined together with high reliability, and a method for producing the same.

[0006]

The present invention was obtained by investigating what is responsible for the excellent weldability of both spheroidal graphite cast iron members and steel members and the reliability of the joint strength at the weld boundary. It is a thing.

The first invention is that a spheroidal graphite cast iron member and a steel member are welded by a welding material of stainless steel,
It is a welded composite part in which the thickness of the chill structure layer and / or the hardening matrix structure layer formed by the heat effect of welding is 0.7 mm or less at the weld boundary portion on the spheroidal graphite cast iron member side.

In the following invention, when welding a spheroidal graphite cast iron member and a steel member together by using a welding material of stainless steel,
It is a method for manufacturing a welded composite part, in which welding is performed at a welding speed of 2 m / min or more. The welding speed at the welded portion is the speed at which beads are generated, and is generally 0.3.
It is constructed at a speed of ~ 0.7 m / min.

[0009]

When the spheroidal graphite cast iron member and the steel member are welded with, for example, an austenitic stainless welding material, a chill structure layer and a spheroidal graphite cast iron matrix structure are formed at the weld boundary portion of the spheroidal graphite cast iron member due to the thermal effect of welding. A cured cured matrix texture layer is produced.

In this case, the austenitic stainless welding material has excellent weldability with the steel member, and also has relatively good weldability with the spheroidal graphite cast iron member, and has a chilled structure of the spheroidal graphite cast iron. The occurrence of welding cracks can be suppressed.

Further, by increasing the welding speed from the above-mentioned general speed, the amount of heat applied to the spheroidal graphite cast iron member and the steel member during welding is reduced, and the chill structure and hardening of the spheroidal graphite cast iron at the weld boundary portion are hardened. Suppresses the formation of base tissue,
Prevents weld cracking.

[0012] Here, the total value of the thickness of the chill texture layer and the thickness of the hardened matrix texture layer must be 0.7 mm or less. By doing so, the thickness of the chill structure layer becomes close to nothing, and the occurrence of cracks is not adversely affected.
If the thickness exceeds 0.7 mm, the alloy components are diffused because heating is performed for a long time, and the chill structure layer and the hardened matrix structure layer are prominently present. Reliability is reduced.

In order to obtain the above metal structure, it is necessary to set the welding speed to 2 m / min or more. This speed is 2m
If less than / min, the amount of heat applied to the weld increases, and the chill structure and the hardening of the matrix structure become remarkable, so
It causes weld cracking.

[0014]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 3 shows a situation before carrying out the welding operation of the embodiment of the present invention. The spheroidal graphite cast iron member 3 is fixed to a jig 2 fixed to an upper portion of a table 1 connected to a welding device (not shown) via bolts and nuts 4. At this time, the carbon steel pipe for machine structure, which is the steel member 5, has been previously inserted into the hole of the spheroidal graphite cast iron member 3. The tip portion of the welding torch 7 is installed at an welding site 6 between the spheroidal graphite cast iron member 3 and the steel member 5 while maintaining an angle and interval at which welding is possible. FIG. 2 shows a vertical cross section of the welded portion after welding.

While the table 1 is rotated at a constant speed, at the same time, an austenitic stainless welding material is sent out from the tip of the torch 7 in an argon gas atmosphere to produce the spheroidal graphite cast iron member 3 and the steel member. An austenitic stainless steel welded portion was formed at the welded portion 6 with the steel 5 to complete the welded composite part in which the spheroidal graphite cast iron member 3 and the steel member 5 were joined.

The welding material used is a wire having a diameter of 0.8 mm, the main components of which are C: 0.04% by weight and S
i: 0.45%, Mn: 1.9%, Ni: 13.4%,
It is an austenitic stainless welding material containing Cr: 23.6%. The welding speed is 4 m / min.

FIG. 1 shows the metallographic structure of the weld boundary portion between the spheroidal graphite cast iron member 3 and the welding material 8 at this time.
A hardened microstructure layer having a thickness of 0.35 mm is formed in the base structure of the weld boundary portion, a chill structure is scarcely recognized, weld cracking does not occur, and the reliability is high.

FIG. 4 shows a part of the metallographic structure of the weld boundary portion between the spheroidal graphite cast iron member 3 and the welding material 8 at the same portion as in FIG. 1, which is carried out by the conventional general welding method. The same welding material as in the example of the present invention was used, and the welding speed was 0.5 m / min. In the case of this conventional example, the thickness of the hardened matrix texture layer was 0.8 mm, but FIG.
The range of m is shown. The change of the metal structure is clear, the chill structure is recognized, and the structure is a hardened matrix structure. Further, it can be seen that weld cracks C are generated in the spheroidal graphite cast iron member 3 near the weld boundary.

As is apparent from a comparison between FIG. 1 and FIG. 4, good weldability is obtained by using an austenitic stainless welding material and setting the welding speed higher than the conventional general speed. , Was able to provide highly reliable welded composite parts.

[0020]

As described above, the welded composite part of the present invention has no weld cracks and has a structure in which the spheroidal graphite cast iron member and the steel member are joined together through the weld boundary portion having excellent reliability. It is useful as a member, and parts such as flanges, bolts and nuts necessary for mechanical joining are unnecessary, and complicated assembly work is improved.

[Brief description of drawings]

FIG. 1 is a photograph of a metallurgical structure of a welded boundary portion of a working example at 200 times magnification.

2 is a longitudinal sectional view showing a welded joint portion of the embodiment of FIG. 1. FIG.

FIG. 3 is a perspective view showing a welding work situation of the embodiment.

FIG. 4 is a photograph of a metallographic structure of a weld boundary portion 200 times as large as that of a conventional welding method.

[Explanation of symbols]

 1 Table 3 Spheroidal Graphite Cast Iron Member 5 Steel Member (Steel Pipe) 6 Welding Site 7 Torch A Welding Boundary of Example According to the Present Invention B Welding Boundary C by Conventional Welding Method C Weld Crack Position

Claims (2)

[Claims] 1. A spheroidal graphite cast iron member and a steel member are welded together by a welding material of stainless steel, and a chill structure layer and / or a hardening formed at a weld boundary portion on the spheroidal graphite cast iron member side due to a thermal effect of welding. Base tissue layer thickness is 0.7m
A welded composite part characterized by being m or less. 2. A method for producing a welded composite part, which comprises welding the spheroidal graphite cast iron member and the steel member together with a welding material of stainless steel at a welding speed of 2 m / min or more.