JPH11152539A - Graphite cast iron member capable of friction welding, and friction-welded member using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the adverse effect, at the time of friction welding, of graphite which, in graphite cast iron, acts as a lubricant at the time of friction welding and hinders the generation of frictional heat in the part to be welded with pressure and, resultantly, causes impracticability of friction welding because the temp. of the part to be welded with pressure cannot be raised up to a temp. at which welding with pressure becomes possible and to provide a friction-weldable graphite cast iron member in which the above-mentioned adverse effect of graphite at the time of friction welding is prevented and also to provide a friction- welded member obtained by subjecting the above member to friction welding. SOLUTION: In the friction-weldable graphite cast iron member, the adverse effect of graphite is prevented by dissipating graphite from the part between the surface and a position at a depth of at least 2 mm from the surface of the part to be friction welded of the graphite cast iron member or by overlaying the surface of the part to be friction-welded of the graphite cast iron member with a welding material for cast iron to at least >=2 mm thickness. Further, the friction welded member can be obtained by applying friction welding to the mutually friction-weldable graphite cast iron members or to the friction weldable graphite cast iron member in which the adverse effect of graphite is prevented and a steel material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a general machine, a tool,
The present invention belongs to the technical field of cast iron members used for components such as pipe joints, and more specifically, to the technical field of graphite cast iron members capable of friction welding and the friction welding members thereof.

[0002]

2. Description of the Related Art Cast iron castings are widely used as mechanical parts, tools, pipe joints, and other members because they can produce a large number of parts having complicated shapes and parts having the same shape as cast. However, cast iron castings have a high carbon content,
Particularly in a graphite cast iron casting, this carbon cannot be easily welded because it is interposed in the casting as graphite. For this reason, covered arc welding, Tig welding, etc. are performed under sufficient control of welding conditions.

[0003]

As described above, a cast iron casting is capable of relatively easily producing a large number of components having the same shape in a complicated manner. Therefore, it is possible to weld a cast iron member or a cast iron member and a steel member. Parts are required. In addition, since a large number of members having the same shape are welded, it is desirable to use friction welding that provides stable joint quality. However, in graphite cast iron members, graphite in graphite cast iron becomes a lubricant during friction welding to prevent the generation of frictional heat at the welded portion, and the welded portion does not rise to a temperature at which the welded portion can be welded, so that friction welding cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a friction-welded portion of a graphite cast iron (flake graphite cast iron, black core malleable cast iron, CV graphite cast iron, spheroidal graphite cast iron) member. By eliminating the graphite, or by overlaying the surface layer portion of the friction welding portion with a welding material for cast iron, friction welding capable of preventing the adverse effect of the graphite that hinders the generation of frictional heat at the time of the above friction welding is possible. An object of the present invention is to provide a graphite cast iron member and a friction welding member obtained by friction welding the same.

[0005]

The gist of the present invention is to eliminate at least 2 mm of graphite from the surface of the graphite welded iron member at the friction welded portion, or to make the surface of the graphite welded iron member at the friction welded portion a cast iron welding material. At least 2mm
This is a graphite cast iron member that can be friction-welded by preventing the adverse effect of graphite by being overlaid.

[0006] A friction-welded member obtained by friction-welding graphite cast iron members capable of being friction-welded to prevent the above-mentioned adverse effect of graphite or a friction-weld graphite cast-iron member that prevents the adverse effect of graphite to steel.

[0007] Graphite cast iron members (hereinafter simply referred to as cast iron members)
In the method of eliminating graphite on the surface layer at the friction welding part of the present invention (hereinafter referred to as degraphitization treatment), a cast iron member is exposed to a high-temperature oxidizing atmosphere, and at this time, the surface of the cast iron member is oxidized by a carbon oxidation reaction. By reducing the carbon content of the cast iron and breaking the equilibrium between the carbon and graphite in the cast iron, the graphite is decomposed into carbon and dissolved in the cast iron as solid solution carbon or cementite, thereby reducing the graphite in the cast iron. Is to disappear. At this time, the graphite on the surface of the cast iron is directly oxidized and disappears.

That is, the carbon in the cast iron is oxidized by the following reaction to reduce the carbon content in the cast iron.

2C (graphite and carbon on cast iron surface) + O ₂ (oxygen in oxidizing atmosphere) → 2CO ₂ CO + O ₂ (oxygen in oxidizing atmosphere) → 2CO ₂ C (graphite and carbon on cast iron surface) + CO ₂ (in oxidizing atmosphere) Carbon dioxide) → 2CO

[0010] The above reaction oxidizes carbon on the surface of the cast iron member.
It is removed and the carbon content on the surface of the cast iron member is reduced. As a result, a difference in carbon content occurs between the surface of the cast iron member and the inside thereof, and the carbon inside diffuses to the surface due to the difference in the carbon content.
Since oxidation / removal of carbon is continuously performed on the surface, diffusion of internal carbon to the surface is also continuously performed. Therefore, the surface layer of the cast iron member has a low carbon content and becomes a low carbon ferrite region.

The carbon content in the interior of the cast iron member is reduced by the diffusion of carbon to the surface, which breaks the equilibrium between the carbon and graphite in the cast iron, and the graphite is decomposed into carbon and carbon dissolved in the cast iron. Alternatively, the graphite in the cast iron disappears as much as the cementite melts into the cast iron. In this way, the graphite in the cast iron gradually disappears from the surface toward the inside.

The oxidizing atmosphere used in the degraphitization treatment is, as in the heat treatment in the production of white-heart malleable cast iron, a magnetite as a solid oxidizing agent adjusted to a degree of oxidation that does not generate iron oxide on the surface of the cast iron member by 60% or more. Buried in iron sand contained or the oxidation degree of the oxidizing gas (CO-CO ₂ ) atmosphere is CO / (CO + CO ₂ ) =
It can be obtained by adjusting the target to 0.75. In addition,
By adding H ₂ O to this oxidizing gas and adding about 10% of H ₂ , the uniformization of the gas atmosphere in the degraphitizing furnace can be promoted. The degraphitization treatment is performed in the austenitic temperature range of 910 ° C or higher, at which the diffusion of carbon in the cast iron is accelerated.The upper limit of the treatment temperature is such that the cast iron member to be degraphitized is not deformed and partial melting at the crystal grain boundaries, etc. A temperature that does not occur. The optimum processing time is determined for each processing depending on the thickness of the cast iron member to be degraphitized and the predetermined depth of the degraphitized layer. The degraphitization treatment requires a long time, but has the advantage that a large number of members can be treated at the same time.

[0013] The graphite disappearance depth of the surface layer at the friction welding portion is determined by the amount of upset at the time of friction welding. If graphite of at least 2 mm is eliminated from the surface, a sound friction welding member of a joint can be obtained. be able to.

In the case where the surface at the friction welding portion is clad using a welding material for cast iron, the cladding is performed by Tig welding using an iron core wire or a Ni-containing iron core wire under an Ar gas atmosphere. The thickness of the build-up may be a thickness that does not adversely affect the graphite in the cast iron present at the welded portion at the time of friction welding,
Its thickness shall be at least 2 mm from the surface. If the thickness is increased to 2 mm or more in this way, a sound friction welding member for a joint can be obtained. The proper use of the core wire is performed according to the strength of the cast iron member and the chemical composition of the steel material that is friction-welded to the cast iron member. Although this overlay method is a process for each member, it has the advantage that it can be performed in a shorter time than the degraphitization process.

According to the above-described method, at least 2 mm or more of graphite is eliminated from the surface of the friction-welded portion of the graphite cast iron member, or the surface of the friction-welded portion of the graphite cast iron member is overlaid with at least 2 mm of the pressure-welded material for cast iron. By doing so, the graphite cast iron member that has prevented the adverse effects of graphite can be friction welded, and the cast iron members can be friction welded with each other or this cast iron member and steel, thereby obtaining a friction welded member of a sound joint. it can.

[0016]

Embodiments of the present invention will be described below. Friction welding was performed using materials having the chemical components and strengths shown in Table 1, and a tensile test was performed to confirm the soundness of the joint. Prior to the friction welding, the welded portions of the graphite cast iron members were overlaid by degraphitizing treatment or Tig welding.

[0017]

[Table 1]

Example 1 Two sets of friction welded joints made of a combination of SS400 and CV graphite cast iron and a combination of SS400 and spheroidal graphite cast iron shown in Table 1 were manufactured and subjected to a tensile test. The shape of each material before friction welding is 16mm in diameter
It is a round bar. Each graphite cast iron material was filled in a pot containing iron sand containing at least 60% of magnetite, and the degraphitization treatment was performed in a sealed state. The heat pattern at this time is to raise the temperature from room temperature to 1050 ° C in 6 hours, hold at this temperature for 48 hours, cool down to 900 ° C over 18 hours after holding, and then
It was left to cool in the pot. The oxidation degree is 1050 ° C and CO / (CO +
CO ₂ ) ≒ 0.75. Degraphite depth after degraphitization treatment is 2.9mm
Met. After performing pressure welding under the friction welding conditions shown in Table 2,
It was processed into a test piece having a diameter of 10 mm and a parallel part length of 30 mm, and a tensile test was performed. Table 2 shows the results.

Table 2 shows the friction welding conditions and the tensile strength. As shown in Table 2, in a tensile test of a CV graphite cast iron whose surface layer has been degraphitized and a spheroidal graphite cast iron with a SS400 round bar friction-welded, both fractured at the welded site. This is because a hardened layer, which is considered to be a thin heat-affected zone of 0.5 mm or less, which is about HV10 harder than the base metal just below the cast iron side of the joint surface, is observed, and acts during the tensile test, and the tensile strength is higher than that of the base metal. It is considered to be However, it is sufficiently possible to use a CV graphite cast iron and a spheroidal graphite cast iron whose surface layer has been degraphitized and joined by friction welding to a carbon steel pipe for piping used for a low pressure fluid of 100 N / mm ² .

[0020]

[Table 2]

EXAMPLE 2 A pipe joint (A) for a car engine made of CV graphite cast iron having the same chemical composition as the CV graphite cast iron shown in Table 1 and a pipe joint (B) made of a spheroidal graphite cast iron having the same chemical composition as the spheroidal graphite cast iron ) Was subjected to degraphitization treatment under the same conditions as in Example 1 and then friction welded to STKM 13 A (carbon steel pipe for machine structure) shown in Table 1. The degraphitized depth after the degraphitization treatment was 2.6 mm. Table 3 shows the friction welding conditions.

Automotive Engine Piping Joint (A) and STKM 1
Fig. 1 shows the shape of the press-fitting joint between 3A and the pipe joint (B) for automotive engine and STKM 13A. As shown in FIG. 1, burrs are provided at the friction-welded portions of the pipe joints (A) and (B) so that burrs at the time of pressing do not enter the pipe. Thus, the bulge suppressing wall 2 was provided at the press-welded portion, and a press-welded joint was manufactured under the friction-welding conditions shown in Table 3. The welding state of the friction welding was evaluated and determined from the amount of burrs generated at the welded portion and its form. The joint state of the joints (A) and (B) in the example could be considered to be normal from the state of occurrence of burrs. In addition, a sound joint was obtained without any burrs in the pipes of any of the friction welding joints.

[0023]

[Table 3]

Example 3 Three sets of friction welded joints made of a combination of SS400 shown in Table 1, flaky graphite cast iron, CV graphite cast iron, and spheroidal graphite cast iron were manufactured and subjected to a tensile test. The shape of each graphite cast iron material before friction welding is a round bar with a diameter of 20 mm, and SS400 is a round bar with a diameter of 13 mm. Prior to the friction welding, the friction welding site of each graphite cast iron material was overlaid by Tig welding. As shown in Fig.2, as shown in Fig.2, a recess with a diameter of 15.5mm and a depth of 4mm was provided, and an iron core wire (2mm in diameter) of the chemical composition shown in Table 4 was used to fill this recess. The cladding was performed by Tig welding.
Thereafter, the overlay was smoothed by a grinder and subjected to friction welding. Table 5 shows the friction welding conditions and tensile test results. The tensile test was performed with burrs.
In order to observe the bonding state of the press-contact portion, the press-contact portion was cut vertically to observe the press-contact portion.

As described above, the welded portion was cut vertically and the welded state of the welded portion was observed. No defects were found in any of the welded portions, and a sound joint was obtained. The tensile test result is
As shown in Table 5, there was no fracture at the joint, and the fracture position was on the flaky graphite cast iron and the base material of SS400. Therefore, it can be said that the strength of each press contact portion is equal to or higher than the base material strength of each graphite cast iron. The reason why the flaky graphite cast iron has a smaller margin than that of the CV graphite cast iron and the spheroidal graphite cast iron in Table 5 is presumed to be due to the fact that the thermal conductivity of the flaky graphite cast iron is 20 to 50% larger than other cast irons. You.

[0026]

[Table 4]

[0027]

[Table 5]

Example 4 Three sets of friction welded joints made of a combination of SS400 shown in Table 1, flaky graphite cast iron, CV graphite cast iron, and spheroidal graphite cast iron were manufactured and subjected to a tensile test. The shape of each graphite cast iron material before friction welding is a round bar with a diameter of 20 mm, and SS400 is a round bar with a diameter of 13 mm. Prior to the friction welding, the friction welding site of each graphite cast iron material was overlaid by Tig welding. As shown in Fig. 2, the overburden condition is as follows: a recess with a diameter of 15.5mm and a depth of 4mm was provided, and an iron core wire containing Ni with the chemical components shown in Table 4 was filled so as to fill the recess.
2mm), and the cladding was performed by Tig welding under an Ar gas atmosphere. Thereafter, the overlay was smoothed by a grinder and subjected to friction welding. Table 6 shows the friction welding conditions and the results of the tensile test. In addition, although the tensile test was performed in a state with burrs, in order to observe the joining state of the press-contact portion, the press-contact portion was cut vertically to observe the press-contact portion.

As described above, the welded portion was cut vertically to observe the bonding state of the welded portion. No defects were found in any of the welded portions, and a sound joint was obtained. The tensile test result is
As shown in Table 6, there was no fracture at the joint, and the fracture position was on the flaky graphite cast iron and the base material of SS400. Therefore, it can be said that the strength of each press contact portion is equal to or higher than the base material strength of each graphite cast iron. Moreover, even if the overlaying is performed by Tig welding using the iron core wire (Example 3) or the Ni-containing iron core wire, a sound joint is obtained.

[0030]

[Table 6]

[0031]

As is apparent from the above description,
According to the present invention, the adverse effect of graphite in graphite cast iron, which becomes a lubricant during friction welding and hinders the generation of frictional heat at the welded portion, is suppressed by degraphitization treatment or build-up welding, so that the graphite cast iron member Friction welding becomes possible, and a friction welding member made of a graphite cast iron member of a sound joint can be obtained.

[Brief description of the drawings]

FIG. 1 is a pipe joint (A) for an automobile engine according to a second embodiment;
It is a figure which shows the shape of the friction welding joint part of (B) and STKM13A (carbon steel pipe for machine structures).

FIG. 2 is a view showing a build-up state of a press-welded portion of each graphite cast iron material of Examples 3 and 4, and a shape of a friction welding joint between each graphite cast iron material and an SS400 material.

[Explanation of symbols]

1… STKM 13 A (carbon steel pipe for machine structure), 2… walls to prevent bulging, 3… graphite cast iron material, 4… SS400 material, 5
... Overlay, A: CV graphite cast iron automotive engine piping joint, B: Spheroidal graphite cast iron automotive engine piping joint.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C21D 5/00 C21D 5/00 DB23K 103: 06

Claims (4)

[Claims] 1. A graphite cast iron member capable of friction welding, characterized in that at least 2 mm or more of graphite has been eliminated from the surface of the graphite cast iron member at the friction welding site. 2. A graphite cast iron member capable of friction welding, characterized in that a surface of the graphite cast iron member at a friction welding portion is overlaid with a welding material for cast iron at least 2 mm or more. 3. A friction welding member according to claim 1, wherein the graphite cast iron members capable of being friction welded are friction welded with each other. 4. A friction welding member characterized in that a frictionally weldable graphite cast iron member and a steel member according to claim 1 or 2 are friction welded.