JP2003025075A - Friction press-joining method for cast iron and joined part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a friction press-joining method for cast iron with which an oxide film is not entrapped in the joined surface and joining strength is not lowered and to provide a joined part which is joined with such the friction press-welding method, provided with a sound joined part and having excellent joining strength. SOLUTION: When the friction press-joining is applied to two members at least one of which is composed of the cast iron, a friction process is started by forming the surface roughness on the pressure-contacting surface to be <=10 Ra and, after raising the joining interface temperature to >=800 deg.C and a temperature lower than the fuse-starting temperature, an upset pressure is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction welding method for cast iron used for joining members made of cast iron or for joining a cast iron member and another metal member, and a joined part joined by the friction welding method. It is a thing.

[0002]

In friction welding, members to be joined are abutted against each other, and the members are subjected to relative rotational movement, and the frictional heat generated at the abutting faces is used to heat the joined faces. However, it is a method of joining by applying pressure, and has an advantage that it can be applied not only to joining of similar materials but also to joining of different materials.

As a method of joining cast irons using such friction welding, for example, the one described in Japanese Patent Publication No. 49-4150 is known, and as shown in FIG. The temperature is raised to the melting start temperature, for example, about 1140 ° C. or higher in the case of spheroidal graphite cast iron, and the upset pressure is applied while the molten phase is stable, so that the molten phase is discharged from the joint interface. .

However, in the conventional friction welding method as described above, since the members to be welded rotate at a high speed in the friction process in the state where the bonding interface is melted, the molten phase is oxidized during the high speed rotation, and Occlusion of the oxide film on the bonding surface sometimes occurred. If this oxide film cannot be completely discharged in the upset process, metal bonding at the joint surface cannot be performed, resulting in an internal notch defect,
There is a problem that the bonding strength is significantly reduced.

FIG. 7 shows spheroidal graphite cast iron FCD400 (JI
S G 5502) is a microstructure photograph showing an example of an oxide film produced on the joint surface when the two are joined by the above friction welding method, and the oxide film of cast iron becomes slag-like and remains on the joint surface. You can see how they are doing. Due to the presence of such an oxide film, in cast iron containing graphite such as spheroidal graphite cast iron, reprecipitation of graphite during the cooling process is concentrated on the discontinuous surface of these base metal and oxide film, There is also a problem that it is one of the causes of the decrease, and elimination of these problems has been a conventional problem in friction welding of cast iron.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in conventional friction welding of cast iron, and does not cause the oxide film to be entrained in the joint surface, thereby not lowering the joint strength. It is an object of the present invention to provide a friction welding method and a joining component which is joined by such a friction welding method and has a sound joining portion and is excellent in joining strength.

[0007]

In the friction welding method for cast iron according to the present invention, when two members, at least one of which is made of cast iron, are friction-welded, the surface roughness of the contact surface is Ra10.
The friction step of the cast iron is characterized in that the friction step is started as follows, the joining interface temperature of both members is raised to 800 ° C. or higher and lower than the melting start temperature, and then the upset pressure is applied. Such a structure in the pressure welding method is used as a means for solving the above-mentioned conventional problems.

The joint part according to the present invention is joined by the friction welding method described above, and is characterized in that the CE value (carbon equivalent) of cast iron is 3.8 to 4.4%. As a preferred form thereof, the cast iron further contains 0.1 to 1.0% of Mo, and the joining part by friction welding is integrally joined to the exhaust manifold for an internal combustion engine and the catalyst container. Characterized by being a body.

The carbon equivalent and the CE value in the present invention mean those calculated by the following equations. Moreover, the percentage value of each component is based on the mass ratio. CE value (carbon equivalent) = C% + (1/3) Si%

[0010]

1 is a graph showing a process pattern of a friction welding method for cast iron according to the present invention. As shown in FIG. 1, at least one of the friction welding methods is cast iron. With the joining surfaces of the two members made of abutting against each other, one member is rotated, and after reaching a predetermined number of rotations, pressure is applied between the members and the temperature of the joining interface is 800 ° C or more due to frictional force. , And a friction step of heating to a predetermined temperature lower than the melting start temperature of the cast iron, and after the joint interface temperature of both members has risen to a predetermined temperature, the rotation speed is reduced or stopped to a predetermined upset pressure. Is applied to join the two members together.

In the friction process, as the temperature of the joint surface rises, impurities existing at the joint interface are discharged as burrs from the joint interface as a result of plastic flow in the vicinity of the joint surface, which has become high temperature, and clean metal surfaces. Come into contact. At this time, it is necessary that the interface temperature is a high temperature of 800 ° C. or higher in order to soften the interface sufficiently to cause metal bonding. Further, in order to prevent oxides from being generated and being caught in the bonding interface, the interface temperature is set to the melting point of the cast iron that is the member to be bonded (for example, spheroidal graphite cast iron FCD40).
In the case of 0, it is necessary to lower the temperature to about 1140 ° C.) so that no oxide is formed.

In this temperature state (800 ° C. or higher, lower than the melting point of cast iron), by applying a predetermined upset pressure between both members, the interface is sufficiently close to the interatomic distance required for metal bonding, and at the same time, further Due to the plastic flow, impurities on the joint interface are completely discharged as burrs to the outside of the joint surface.

However, in the case where at least one of the pressure contact surfaces is graphite or cast iron containing other dispersed phase, a pressure not affecting the shape or dispersed state of the dispersed phase (in the case of steel materials containing no dispersed phase, There is no choice but to press it at about 1/2 or less). Therefore, even if the temperature is not higher than the melting point, when the initial surface roughness of the pressure contact surface is rough, a gap that cannot be pressure contacted remains in the concave portion of the pressure contact surface during the temperature rising process, and by the air entering there, High-temperature oxidation may proceed in the recesses, and the oxide film may partially remain to reduce the bonding strength. Therefore, the initial surface roughness, that is, the surface roughness of the pressure contact surface at the start of the rubbing process needs to be Ra10 or less.

The upset pressure at this time is generally desired to be in the range of 20 to 70 MPa so that the joint surface becomes sound and the joint strength is improved. That is, when the upset pressure is less than 20 MPa, the plastic flow is not sufficiently performed, and the presence of the micro gap tends to reduce the bonding strength.

On the other hand, when the upset pressure exceeds 70 MPa, the cast iron containing no Mo tends to have a lower tensile strength. This is considered to be because in the spheroidized graphite cast iron, the graphite in the vicinity of the joint surface is deformed and the spheroidization rate is deteriorated, but even in general cast iron, the dispersed phase (for example, flake-like It is considered that the strength is similarly reduced because the graphite) is easily oriented in a specific direction such as the bonding surface direction.

However, by adding Mo to cast iron, the tensile strength can be prevented from lowering even when the upset pressure is further increased to 80 MPa. This is because the change in the shape and dispersed state of the dispersed phase as described above is Mo.
It is thought that this is prevented by the addition of. However, such an effect of Mo is not recognized when the added amount is less than 0.1%, and when the CE value described later is 4.4% or less, Mo is added in excess of 1%. In this case, regardless of the type of cast iron, carbides are likely to be generated, white pig iron (so-called chilling tendency) may occur, and workability and toughness may be deteriorated. Therefore, when Mo is added, It is desirable that the range is within the range of 0.1 to 1.0%.

Regarding the upset time, it is desirable to maintain the pressure up to 700 ° C. as the temperature at which the reprecipitation of graphite from austenite is completed in the cooling process of the upset process and the solid phase diffusion of the interface can be expected.

Carbon equivalent (CE value = C% + 1/3
(Si%), the CE value is preferably in the range of 3.8 to 4.4% from the viewpoint of obtaining stable tensile strength even when the surface roughness of the pressure contact surface before the rubbing step is about Ra10. . That is, when the CE value exceeds 4.4%, it is difficult to obtain a stable tensile strength, and conversely, when the CE value is less than 3.8, the molten metal flowability during casting of cast iron tends to decrease. There is.

FIG. 2 shows the metallographic structure of the joint interfaces (the spheroidal graphite cast iron FCD400s) thus friction-welded together. The oxide inclusions observed in FIG. Is not recognized.

[0020]

EXAMPLES The present invention will be described more specifically below based on examples.

(Example 1) FCD400 (melting point: about 1) specified as a spheroidal graphite cast iron product in JIS G 5502.
Outer diameter consisting of 140 ° C, CE value: 4.4%): 50 m
m, inner diameter: 40 mm, a pipe was prepared, the surface roughness Ra of the pressure contact surface before the friction step was variously changed, and these pipes were butted against each other, and the peripheral speed was 4.5 m / s and the friction pressure was 40 MPa. Then, the cast iron members were friction-welded to each other by heating until the maximum temperature of the joint interface reached 1050 ° C. and applying an upset pressure of 70 MPa.

Then, the tensile test of the obtained joint was conducted to investigate the influence of the surface roughness Ra of the joint surface on the tensile strength. The result is shown in FIG. The tensile test was carried out for two types, that is, the as-pressed state and the ferritic-annealed state after the pressure-welding, and compared with the case of the conventional method.

As is clear from the results shown in FIG. 3, in the case of the conventional method in which the surface roughness of the joint surface exceeds Ra10, a quenching structure is formed by the effect of heating and cooling during friction welding when the pressure welding is performed, and the strength of the matrix is improved. However, the tensile strength is very low due to the notch effect of the oxide film. Similarly, it was found that the tensile strength was reduced by the oxide film even in the ferritic annealing state. On the other hand, according to the method of the present invention in which the surface roughness of the joint surface is Ra10 or less, there is no oxide film on the joint surface, and the joint width becomes wider than that of the base metal due to plastic flow in the vicinity of the joint surface at high temperature. Together with this, it was confirmed that all of the base materials fractured and no fractures were observed from the joint surface, and stable tensile strength was obtained.

(Example 2) A pipe made of spheroidal graphite cast iron FCD400 having a carbon equivalent CE value changed to 5 levels and having the same dimensions (outer diameter: 50 mm, inner diameter: 40 mm) as described above was used. After processing the surface roughness to Ra10, butting in the same manner, the same condition (peripheral speed: 4.5 m /
s, friction pressure: 40 MPa, maximum joint interface temperature: 105
The above cast iron members were friction-welded together at 0 ° C. and an upset pressure of 70 MPa, and the effect of the CE value on the tensile strength was investigated. In this case, the tensile test was carried out only for those which were subjected to ferritic annealing after pressure welding.

The result is shown in FIG.
When the CE value exceeds 4.4%, stable tensile strength cannot be obtained, whereas when the CE value is 4.4% or less, the maximum temperature during the friction process is within the temperature range of the pressure contact surface. It was confirmed that by concentrating in the vicinity, the action of discharging impurities at the joint interface due to plastic flow can be strengthened, and stable tensile strength can be obtained even if the surface roughness of the pressure contact surface before the friction step is about Ra10.

Example 3 Spheroidal graphite cast iron FCD400 (melting point: about 1140 ° C., C similar to that used in Example 1)
E value: 4.4%) and a spheroidal graphite cast iron FCD400 in which 1% of Mo is added to the spheroidal graphite cast iron of the component, and a pipe having similar dimensions (outer diameter: 50 mm, inner diameter: 40 mm) is used. After processing the surface roughness of the joining surface to Ra10, butting them in the same manner and heating under the conditions of peripheral speed: 4.5 m / s and friction pressure: 40 MPa until the maximum temperature of the joining interface reaches 1050 ° C. Upset pressure to 10
MPa, 20 MPa, 30 MPa, 50 MPa, 70M
The cast iron members were friction-welded to each other by changing the pressure to 7 levels of Pa, 80 MPa and 90 MPa, and the influence of upset pressure and addition of Mo on the tensile strength was investigated. In addition,
Also in this case, the tensile test was carried out only for those which were subjected to ferritic annealing after pressure welding.

The result is shown in FIG.
When the upset pressure is less than 20 MPa, although there is no oxide film, plastic flow does not occur up to the interatomic distance required for metal bonding, so that there is a micro gap and sufficient bonding strength cannot be obtained. confirmed. On the other hand, when the upset pressure was set to 80 MPa or more, it was found that in cast iron containing no Mo, the spheroidization rate of graphite in the vicinity of the joint surface deteriorates, resulting in a decrease in tensile strength.
When Mo is added, the upset pressure is 80 MPa.
Even in the case of, no decrease in tensile strength was observed.

[0028]

As described above, according to the method for friction welding of cast iron according to the present invention, when two members, one or both of which is cast iron, are friction welded, the surface roughness of the contact surface is Ra10 or less. As a result, the friction step is started, and the upset pressure is applied after the joining interface temperature is raised to 800 ° C. or higher and lower than the melting start temperature. It is possible to prevent an oxide film from intervening at the interface, to secure the soundness of the joint portion, and to obtain a friction-bonded joint having sufficient joint strength, which is an extremely excellent effect.

The joined part according to the present invention has a CE value of 3.8 to 4.4% by the friction welding method for cast iron.
Cast iron, CE value of 3.8 to 4.4%, and Mo
Since the cast iron having a content of 0.1 to 1.0% is joined, a very excellent effect that a sound joining portion is provided and higher joining strength can be stably obtained is brought about.

Furthermore, when these cast irons having a low CE value are used, the pressure contact surface has a predetermined temperature (800 ° C. or higher and lower than the melting start temperature) in the friction process due to an increase in the amount of heat generated at the pressure contact surface and low thermal conductivity. There is also an effect that it is possible to shorten the time until reaching. In particular, when Mo is added to the base material cast iron, the friction pressure and the upset pressure can be further increased, and this effect becomes even greater.

[Brief description of drawings]

FIG. 1 is a graph showing a process pattern of a friction welding method for cast iron according to the present invention.

FIG. 2 is a microstructure showing a state of a joint interface of cast iron joined by a friction welding method according to the present invention.

FIG. 3 is a graph showing the influence of the surface roughness of the joining interface on the tensile strength of cast iron joined by friction welding.

FIG. 4 is a graph showing the influence of CE value on the tensile strength of cast iron joined by friction welding.

FIG. 5 is a graph showing the effects of upset pressure and addition of Mo on the tensile strength of cast iron joined by friction welding.

FIG. 6 is a graph showing a process pattern in a conventional friction welding method for cast iron.

FIG. 7 is a microstructure showing a state of a joint interface of cast iron joined by a conventional friction welding method.

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Claims (4)

[Claims] 1. When friction-welding two members, at least one of which is made of cast iron, the surface roughness of the pressure-contact surface is Ra10.
A friction welding method for cast iron, comprising the step of starting the friction step as described below, raising the joining interface temperature of both members to 800 ° C. or higher and lower than the melting start temperature, and then applying an upset pressure. 2. A joined part joined by the friction welding method according to claim 1, wherein the CE value (carbon equivalent) of cast iron is 3.8 to 4.4%. 3. The friction welding method according to claim 1, wherein the cast iron has a CE value (carbon equivalent) of 3.8 to 4.4%,
A joined component having a Mo content of 0.1 to 1.0%. 4. The integrated body of an exhaust manifold for an internal combustion engine and a catalyst container as claimed in claim 2, wherein
Joined parts as described.