JPH0724945B2 - Laser welding method for sintered materials - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining method for melting and joining porous sintered parts or sintered parts mainly used in power transmission systems of automobiles.

[0002]

2. Description of the Related Art Joining steel members is done by general arc welding,
Alternatively, it is widely performed by high energy density beam welding such as electron beam and laser beam. However, in the case of a sintered material, since it is porous, when the welding is performed by these methods, the holes of the base material are aggregated, large blowholes are formed in the weld metal, and the strength of the welded portion cannot be ensured. , Cracks occur. For this reason, conventionally, the following methods have been proposed as a method for joining the sintered materials, but each has a problem.

Method by brazing When the brazing material is selected and the brazing conditions are difficult and the wettability of the brazing material is too good, the brazing material is absorbed in the pores of the base material and the brazing at the bonding interface is insufficient. If the wettability of the material is poor, good bonding cannot be achieved especially to a sintered material having a medium or high carbon composition. In addition, voids may grow around the bonding interface during brazing, making it difficult to obtain stable strength.

A method similar to shrink fit, which utilizes a difference in linear expansion coefficient of two members to join at the time of sintering, or after shrink fitting by shrink fit or cold fit. The condition of use is limited for those joined by such a method.

Method by Infiltration This is a method in which an infiltrant such as copper is set in the joint of two members and the infiltrant is melted to fill the pores of the joint with molten metal. Because it depends on the infiltrant,
The strength of the joint is significantly lower than that of the base metal. In addition, joints that are joined by this method are likely to deteriorate.

A method of performing high energy density beam welding after infiltration, which is a method disclosed in Japanese Patent Application Laid-Open No. 2-160185.
By filling the holes with an infiltrant and then beam welding, there is a possibility that it will be possible to improve the occurrence of blowholes, but no measures are taken against the occurrence of other defects. . That is, usually 0.4 to 1% of carbon is added to the sintered material in order to secure the strength, but when this is welded by high energy density beam welding with a fast cooling rate, low temperature cracking occurs. . Further, since it is an infiltrant typified by copper, the copper content in the weld metal increases, and together with impurities such as S in the base metal, the hot cracking susceptibility is significantly increased,
High temperature cracking (solidification cracking) of weld metal is unavoidable. In addition, infiltration and beam welding are required in two steps, and it is difficult to say that this is an advantageous method in terms of productivity.

As described above, the conventional joining methods and filler materials are insufficient in terms of prevention of defects, strength of joints, productivity and toughness of joints, and no jointing method that can satisfy all of them can be found. The current situation is that there are none.

[0008]

If the above-mentioned high energy density beam welding can be applied to the joining of sintered materials or the joining of sintered materials and steel materials, penetration depth, strength, productivity,
It is considered to be advantageous in terms of distortion. However, since the sintered material usually has a considerably high C content and the presence of pores, defects such as cold cracking and blowholes cannot be avoided. Therefore, in order to put this into practical use, it is necessary to prevent the formation of cold cracks, blowholes, etc., and to obtain a welded portion having an appropriate strength. Furthermore, unless welding itself can be performed stably, it cannot be put to practical use in a field where productivity is important.

The present invention has been made in order to meet such a demand, and an object thereof is to provide a joining method in which defects such as low temperature cracks and blow holes do not occur in joining of sintered materials by laser welding. It is what

[0010]

In order to solve the above problems, as a result of intensive studies by the present inventors, the present inventors found out the conditions unique to laser welding of sintered materials, and made the present invention here. is there.

That is, according to the present invention, when the porous sintered parts are joined together or when the sintered parts and the steel material are joined, Cr,
At least one of Mo and Si, and Ni, C and Mn
Laser of a sintered material, characterized by irradiating with a laser beam while supplying a component-based filler material containing at least one of Al, Ti, Zr and V The main point is the welding method.

The present invention will be described in more detail below.

[0013]

[Function] Sintered materials used as mechanical parts are generally
To improve the strength, 0.4% or more of C is added to pure iron powder or alloy powder, and Cu of about 2.5% or less as a sintering aid is mixed with a binder to form a green compact. And sintered. When such a sintered material is welded by high energy density beam welding, as described above, the blowholes due to the holes in the base material are generated, and the low temperature crack is generated.

On the other hand, the operation of the present invention is as follows. First, by using laser welding as the welding method, a deeper penetration depth can be obtained with less strain. Further, the laser welding that can be welded in the atmosphere is more advantageous than the electron beam welding method in which welding is generally performed in a vacuum with respect to the generation of blow holes due to the holes in the base material.

However, since the above-mentioned defects cannot be prevented by simply laser welding, a filler material (filler wire) is used in the present invention. That is, in order to prevent low temperature cracking due to martensitic transformation of weld metal, austenite forming elements such as C, Ni and Mn are added to C
For ferrite forming elements represented by r, Mo and Si,
By using the wire contained in the proper ratio,
The structure of the weld metal becomes austenite or a mixed structure of austenite and martensite, martensite transformation is suppressed, and low temperature cracking can be prevented.

On the other hand, the occurrence of blowholes is prevented by adding at least one of Al, Ti, Zr and V which is a strong deoxidizer in an appropriate amount. These elements are deoxidizing agents and at the same time have a nitrogen absorbing function. That is, since the pores in the sintered material contain not only oxygen but also nitrogen as a matter of course, deoxidizing agents such as Mn and Si are not sufficient to prevent the generation of blowholes. By adding an appropriate amount of the deoxidizing agent, it is possible to completely prevent the generation of blowholes.

The filler materials under the proper conditions in the present invention are shown below.

When high energy density beam welding is performed while supplying a filler metal to a sintered material having a relatively high C content, it is impossible to make the entire weld metal into a filler metal composition. The ratio of the filler material component to the entire weld metal is practically limited to about 50% in consideration of wire supply stability and the like. On such a premise, in order to make the structure of the weld metal austenite or a mixed structure of austenite and martensite of a certain hardness or less (hardness without the problem of cold cracking), the following formula is satisfied, and the balance is A component-based filler material that is substantially Fe is suitable.

Y ≧ − (1/3) X + 23 Y ≧ 12 where X = Cr (%) + Mo (%) + 1.5Si (%) Y = 1.2Ni (%) + 20C (%) + 0.8Mn (% )

In the above equation, the X component is Cr, M
It consists of at least one of o and Si, and the Y component is N
It is composed of at least one of i, C, and Mn.

The basic idea will be described with reference to FIG. The base material is an iron-based sintered material containing 0.7% C. In the figure, the region of the white mark or the one-dot white mark on the upper side is a weld of cold cracking and austenite structure (or mixed structure of austenite and martensite structure containing austenite structure to the extent that cold cracking does not occur). The metal is a filler metal component region that can be stably obtained, while the lower black or semi-black region is a region where cold cracking occurs, and martensite structure (or austenite to the extent that cold cracking occurs). It is a region where a weld metal of austenite containing structure and mixed structure of martensite structure is obtained, and the boundary between the two regions is Y = − (1 /
3) X + 23 and Y = 12.

Further, as a measure for preventing blowholes, in the present invention, at least one of Al, Ti, Zr and V is added to the filler material, but the proper amount is 0.3 to 5%. As mentioned above, Al, Ti, Zr, and V are strong deoxidizers and have an effect on nitrogen absorption.
Seeds are added in appropriate amounts (0.3-5%). If the Mn content is fairly high, the content of these elements may be low,
Even in that case, 0.3% or more is necessary.

By the way, when laser welding is performed while supplying the filler material having the above composition, it cannot be said that the technique can be practically used unless a stable and sound weld is obtained under various welding conditions. Therefore, the diameter of the filler metal is 1.
It is preferable to set it to 6 mmφ or less and to appropriately regulate the wire supply speed in accordance with the laser output condition.

That is, in the case of performing laser welding while supplying the above-mentioned filler metal, it is necessary to supply the filler metal in an amount according to the laser output or welding speed to obtain a desired weld metal structure. As a result of various experiments conducted by the inventors of the present invention, it was found that the required wire supply amount depends largely on the laser output and not on the welding speed. Specifically, the amount of the filler material supplied during welding is y ≧ 425x−850 (where x:
Laser output (KW), y: Wire supply amount (mm ³ / min))
The filler metal is supplied so as to satisfy the above condition. This limiting condition is for a wide laser output or welding speed condition,
It is a filler material supply condition that can obtain a sound weld.

The filler material according to the present invention may be either a solid wire or a cored wire, and the solid wire is excellent in supply stability, and can be supplied more stably if it has a strand structure.

Next, examples of the present invention will be described.

[0027]

Example 1 This example is an example of laser welding of sintered materials.

[Table 1] Sintered material (12t x 2) with chemical composition (wt%) and density shown in
0w x 100l) while supplying filler materials of various chemical components

[Table 2] Laser welding was performed under the conditions shown in. The filler material used is 1.2 mm
φ wire,

[Table 3] It has the chemical composition shown in. Figure 1 shows the welding situation.
After welding, the presence or absence of defects was examined by X-ray inspection and cross-section inspection of the welded portion. The results are also shown in Table 3.

FIG. 2 shows the relationship between the chemical composition of the filler metal and the presence / absence of defects in the test results. From the figure, Y is-(1/3) X + 32 or more and 12 or more chemical components, and contains at least one of Al, Ti, Zr and V, and the total amount thereof is 0. .3-5
It is clear that both the vacancy defect and the low temperature crack can be prevented by using the filler material in the range of 0.1% and adjusting the filler material supply amount appropriately. The welding material supply rate in this test is based on the laser output and welding speed conditions.
Since it is close to the limit speed at which stable supply is possible, it was judged that a filler metal that could not prevent defects under the test conditions had a practical problem.

[0029]

Example 2 This example is an example of laser welding of sintered materials. For the sintered material (12t × 20w × 100l) shown in Table 1, 0.8mmφ, 1.0mmφ and 1.2mmφ for the filler materials having the compositions of No. 20 and No. 24 shown in Table 3, respectively. ,
Using the one with 1.4 mmφ,

[Table 4] Laser welding was performed under various welding conditions shown in. After welding, the presence or absence of defects was examined in the same manner as in Example 1. The result is shown in Figure 3.
Shown in. This figure summarizes the relationship between the laser output / wire supply amount and the weld defect. As shown in the figure, y ≧
425x-850 (where x: laser output (KW),
y: It was confirmed that a sound welded portion can be obtained under the condition that the wire supply amount (mm ³ / min)) is satisfied.

[0030]

Third Embodiment This example is an example of laser welding of a sintered material and a steel material. The sintered material (12t × 20w × 100l) shown in Table 1 and the S45C steel material (12t × 20w × 100l) were butted against each other, and a laser welding test of different materials was conducted. The filler material used had a chemical composition of No. 24 shown in Table 3 and a wire diameter of 1.2 mmφ. Laser welding conditions are welding speed 1.5 m / min, output 5 kW, wire feed speed 2 m / min (wire feed amount 22
62 mm ³ / min). After welding, the presence or absence of defects was examined in the same manner as in Example 1, and no defects were found.
It was confirmed that a sound weld was obtained.

[0031]

As described in detail above, according to the present invention,
Reliable because, in the joining of porous sintered parts with high C content or between sintered parts and steel, a sound weld can be obtained which was not obtained by the conventional method and laser welding can be applied. It is possible to provide a joining technique having high productivity as well as high productivity.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a procedure of laser welding and a welding condition.

FIG. 2 is a diagram showing a relationship between a chemical composition of a filler material and a defect.

FIG. 3 is a diagram showing a relationship between a laser output / wire supply amount and a defect in a welded portion.

[Explanation of symbols]

 1 Base Material 2 Filler Material 3 Laser Extraction Nozzle 4 Laser Beam 5 Gas Shield Nozzle 6 Weld Bead

Claims (3)

[Claims] 1. When joining porous sintered parts to each other or the sintered parts and a steel material, at least one of Cr, Mo and Si and at least one of Ni, C and Mn are used. , Al, Ti, Zr, and V, while supplying a component-based filler material containing at least one of Al, Ti, Zr, and V while irradiating a laser beam. 2. The composition of the filler material is Y ≧ − (1/3) X +
23, Y ≧ 12 (where X = Cr (%) + Mo (%) + 1.5
Si (%), Y = 1.2Ni (%) + 20C (%) + 0.8Mn
(%)), At least one of Al, Ti, Zr and V is contained in a total amount of 0.3 to 5%, and the balance is substantially Fe. Diameter is 1.6
The method according to claim 1, which is less than or equal to mm. 3. The amount of filler material supplied during welding is y ≧ 425x
The method according to claim 2, which satisfies −850 (where x: laser output (KW), y: wire supply amount (mm ³ / min)).