JP2000087116A - Weldable sintered parts and their manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain weldable parts in which joining between a green compact and a steel material part can be completed simultaneously with sintering/alloying of the green compact by a single process by providing a member made of sintered alloy and a member made of weldable steel material, where either of these members is provided with a hole or a recess and the other is provided with a shaft or a projection, and fitting the hole of the member having a hole or a recess and the shaft of the member having a shaft or a projection together to carry out joining. SOLUTION: When a member (inner member) composed of steel material and having a shaft or a projection and a member (outer member) composed of green compact and having a hole or a recess are fitted and sintered, a green compact having a composition where the amount of expansion in a high temperature region of >=800 deg.C becomes smaller than that of the steel material is used. Further, it is preferable that, when an outer member composed of steel material and an inner member composed of green compact are fitted and sintered, a green compact having a composition where the amount of expansion in a high temperature region of >=800 deg.C becomes larger than that of the steel material is used. As for a fit tolerance between the hole of an outer member and the shaft of an inner member, running fit of <=5 μm clearance or close fit of <=60 μm interference is preferred.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered machine part which can be attached to another part or a machine by welding.

[0002]

2. Description of the Related Art A major feature of powder metallurgy in the manufacture of mechanical parts is that a uniform product can be mass-produced at a higher efficiency and at a lower price than cutting and other processing methods, and the product (sintered part). In addition, there is an advantage that characteristics which are not included in parts derived from ingots, such as oil-impregnating properties and weight reduction due to the porosity specific to sintered alloys, can be used as advantages. However, the welding of a sintered component to other components is generally considered unsuitable because of the negative effect of its porosity on the welding of sintered components to other components.

[0003] The reason is that the conductivity of heat and electricity is inferior due to the porosity, the gas tends to remain in the pores and blowholes are easily generated in the weld, and the carbon content is generally low due to the use as a mechanical part. This is because, due to its high cost, quenching cracks due to transformation strain are likely to occur. Incidentally, laser welding using a filler wire of a special composition is possible even in the case of high carbon sintered parts, but this method is not generally used because the cost is extremely high.

[0004]

Therefore, conventionally, high-density, low-carbon sintered parts are only spot-welded, and in many cases, keyways are provided in joining means other than welding, for example, both in the case of a gear and a shaft. To fix it with a key, or to join a sheet metal member to the side of a toothed pulley, make a hole in both sides and fasten with bolts, or use a sintered part if welding is essential They forgot to use parts derived from ingot material. An object of the present invention is to solve such inconveniences and to develop a machine part which can be welded to other members while making use of the features of powder metallurgy at main parts.

[0005] Taking an internal gear pump as an example of a machine part having a shape suitable for powder metallurgy, the inner rotor (external gear) has a simple shape with a certain number of shaft holes on the inside, but has a simple shape on the outside. The formation of the tooth profile portion is more advantageously performed by powder molding than by machining (gear cutting). The reverse is true for outer rotors (internal gears).
Molding is desirable for forming the inner tooth portion, but the outer portion having a simple shape is not necessarily equal thereto. The toothed pulley described above is the same as the case of the inner rotor.

In the case of such a part, if a part having a complicated shape is made by powder metallurgy, and the other part is made of an ingot material suitable for welding, and if there is a machine part in which both parts are firmly joined, The intended purpose will be achieved. In order to realize this, it is necessary to develop a means for economically mass-producing composite parts joined with a required strength. Incidentally, the ingot in this specification is a general term for ingots of ferrous metals such as pure iron, carbon steel, and alloy steel.

[0007]

Taking the above-mentioned toothed pulley or inner rotor as an example, an outer portion having a toothed portion and an inner portion having a shaft hole are formed by a cylindrical surface having an appropriate radius around the rotation axis. Can be divided into parts. Therefore, the inner portion is formed of a weldable ingot steel (hereinafter sometimes simply referred to as steel), and the outer portion is compacted by powder metallurgy. By sintering the compact in a state where the inner portion is fitted, a sintered machine component having the advantages of powder metallurgy and capable of being welded to a rotating shaft or a sheet metal component is obtained.

According to this method, since the step of sintering the green compact also serves as the step of joining with the steel material, the required steps are shortened and the cost is reduced. In the case of a component having a complicated inner shape like the outer rotor described above, conversely, the powder metallurgy method may be applied to the inner portion and the molten material may be applied to the outer portion.

As described above, one of a portion having a hole or a concave portion (hereinafter referred to as an outer member since it becomes an outside by fitting) and a portion having a shaft or a projection (hereinafter referred to as an inner member) is formed into a green compact, and the other is melted. When joining both members as a lumber and sinter-joining, not only mechanical shrink-fitting but also sintering in a state where the joining surfaces of both members are in close contact, so that the resulting parts have high joint strength. It is necessary to join by solid phase diffusion of alloy components by sintering.

There are various factors, one of which is that the dimensional behavior (expansion / shrinkage) of each member during sintering is important, that is, in the high temperature region where sintering proceeds (iron-based sintering). The material of each member may be selected so that the inner member expands more than the outer member at about 800 ° C. or more for gold, and sintering may be performed with the outer member tightening the inner member.

[0011] When carbon steel S20C is used as an ingot material suitable for welding, an iron-based sintered alloy which does not expand during sintering has a compounding composition of 1.5% copper, 0.7% graphite and the balance of iron. (Compact A), while those that expand more include compacts containing 3% copper, 0.5% graphite and the balance of iron (compact B). In addition, the percentages related to the composition and the like in this specification are weight percentages unless otherwise specified.

Regarding the carbon steel and the green compacts A and B,
The state of thermal expansion due to each heating will be described. The measurement conditions were as follows: the temperature was raised to 1130 ° C. at a rate of 10 ° C./min in a nitrogen atmosphere, and the temperature was kept at that rate for 20 minutes and then lowered at the same rate. First, in the case of carbon steel, since it is an ingot material, dimensional changes due to mere heat except for expansion and contraction due to allotropic transformation (shrinkage due to α-γ transformation during temperature rise and expansion during γ-α transformation during cooling) When the temperature returns to normal temperature, the dimensions return to the original dimensions.

On the other hand, in the case of the green compact A (which becomes a sintered body as the sintering proceeds), allomorph transformation and dimensional change due to heat occur in the same manner as in the case of the ingot material, but are specific to the sintered alloy. As a phenomenon of sintering from the green compact, pores in the gaps of the powder particles are densified (shrinkage) due to the disappearance of pores, and these shrinkages reduce the amount of expansion due to heat, resulting in expansion in a high temperature region. The amount is smaller than carbon steel. Therefore, if the carbon steel is used as the inner member and the green compact A is used as the outer member and the two are fitted together and sintered, the sintering proceeds with the outer member tightening the inner member, and the two are strongly diffusion-bonded. become.

On the other hand, in the case of the green compact B, since the copper content is large, the copper expansion phenomenon peculiar to the iron-copper sintered alloy is remarkably added, so that the shrinkage accompanying sintering is offset. The expansion in the high temperature region is larger than that of carbon steel. Therefore, in the case of the green compact B, it may be used as the inner member and carbon steel as the outer member. Sintering is generally performed by solid-phase sintering, but sintering in a state where a liquid phase is partially generated further promotes diffusion bonding. In this case, if the liquid phase generation amount is within 5%, there is no concern about erosion or shape collapse, but 3%
If stopped within this range, the dimensional accuracy of the sintered body can be maintained in a good state.

Also, the fitting dimension difference (difference between the inner diameter of the hole of the outer member and the outer diameter of the shaft of the inner member) when fitting the two members is important, and the inner member is made thicker ( It is preferable to press-fit the outer member by setting it to an interference fit, and the greater the interference, the higher the degree of adhesion between the two. However, since the compact is more likely to be damaged in the case of fitting with a steel material than in the case of compacts having a buffering action, the interference is smaller than that of the compacts, preferably within 30 μm, and at most When the body is outside, it should be stopped within 60 μm, and when it is inside, it should be stopped by about 40 μm which can be pressed. Also in the case of selecting the fit, the smaller the gap, the better, and it is preferable to keep the gap to 5 μm or less.

As described above, in the case of an iron-based sintered alloy, the dimensional change (expansion) during the sintering process is basically smaller than that of an ingot having the same composition as described above. Several methods are known for making them larger than steel. The use of the copper expansion phenomenon in the green compact B is one of them. The effect is significant when the amount of copper is 1% or more, but 2% is required in order to sufficiently adhere to the fitted outer member to achieve diffusion bonding. The above composition is preferable. In addition, the carbon content of both members was 0.2
% Or more, the expansion amount of the high carbon member (compact) becomes larger than that of the low carbon member.

Incidentally, even when the carbon content of the steel material and that of the green compact are the same, sintering in a carburizing atmosphere increases the expansion of the green compact. As the atmosphere in this case, a purified exothermic gas (for example, carburized butane-modified gas) produced by modifying natural gas or methane-based hydrocarbon is effective. Furthermore, when zinc (such as zinc stearate) is contained in the green compact and is sintered in a carburizing atmosphere, the expansion of the green compact is further increased. This is because when an iron-based green compact containing zinc is sintered in a carburizing atmosphere, a small amount of zinc catalyzes the reaction between iron and carbon in the atmosphere, promoting carburization. by. Therefore, when the compact is fitted as an inner member, these are effective means for expanding the inner member.

On the other hand, when the green compact is used as the outer member, it is desirable to use a non-carburizing atmosphere in order to avoid a slight expansion. In that case, considering economical efficiency, almost no carburizing gas is used. A nitrogen gas atmosphere close to activity or an atmosphere containing nitrogen gas as a main component is particularly preferable. Like this
Unless a means for promoting expansion is used, the sintered alloy relatively shrinks more than steel, so when the green compact is used as the outer member, the material may be pure iron or the same material as the steel of the inner member. . As long as the amount of thermal expansion is not increased (from a steel material), an appropriate alloy component depending on the application can be contained.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Example 1) Assuming a sintered gear in which a shaft hole can be welded, a cylinder (18 mm in outer diameter, 10 mm in inner diameter, 12 mm in length) of carbon steel S20C is used as an inner member. The outer member is fitted to the outer periphery and joined by sintering. For the outer member, a mixture of 1.5% copper, 0.7% graphite and 0.7% of powdered lubricant Acrawax (trade name) added to the balance of iron is 18 mm in inner diameter and 40 m in outer diameter.
m, formed into a disk having a length of 12 mm and a green density of 7.0 g / cm ³ . Both members were fitted together by press-fitting with a interference of 30 μm, and sintered at 1130 ° C. for 40 minutes in a nitrogen atmosphere. The obtained sintered body was set on a material tester, and a destructive test was performed in which the outer member was supported on a gantry and applied to the inner member. As a result, the joining strength of both members was 120 MPa.

(Example 2) A disk of carbon steel S20C (inner diameter 30 mm, outer diameter 36 m) assuming a mechanical part made of a sintered material with a complicated shape on the inner peripheral side and a weldable material on the outer peripheral side
m, 15 mm in length) is used as an outer member, and an inner member is fitted to the inner periphery thereof and joined by sintering. Inside member is copper 3
%, Graphite 0.5% and the balance of iron, and 0.7% of Acurawax (trade name) was added to the mixture to obtain a green density of 7.0 g / c.
It is formed into a cylinder having an m ³ , an outer diameter of 30 mm, an inner diameter of 20 mm, and a length of 15 mm.

[0021] The fitting dimension difference between the two members is set to 10 μm.
As a result of testing the strength of a sintered body obtained by sintering at 1130 ° C. for 40 minutes in a nitrogen gas atmosphere, the joint strength of both members was 110 M
Pa. The copper expansion becomes intense above the melting point of copper (1083 ° C.), and the extent is affected by the amount of copper and other alloy components. For example, aluminum, sulfur, lithium and the like act in a direction to increase the expansion, and boron, carbon and phosphorus act in a direction to suppress the expansion. Accordingly, the desired expansion can be controlled by appropriately selecting the component composition.

Example 3 The composition of the inner member in Example 2 was changed to 1.5% of copper, 0.7% of graphite and the balance of iron, and this compact was fitted to the outer member by press-fitting with an interference of 10 μm. The resultant was combined and sintered at 1130 ° C. for 40 minutes in an atmosphere of modified butane gas. As a result of testing the strength of the obtained sintered body, the joining strength of both members was 110 MPa.

Example 4 The composition of the inner member in Example 2 was changed to 1.5% copper, 0.4% graphite, and 0.7% zinc stearate as a powder lubricant added to the balance of iron. This green compact was fitted with the outer member by press-fitting with an interference of 20 μm, and sintered at 1130 ° C. for 40 minutes in an atmosphere of modified butane gas. As a result of testing the strength of the obtained sintered body, the joining strength of both members was 120 MPa. The strength obtained in each of these examples is a sufficient value as a mechanical part, and therefore, the purpose of integrating the sintered alloy portion and the weldable portion has been achieved.

[0024]

According to the present invention, the joining of the green compact portion and the steel portion which is responsible for weldability is completed in one step at the same time as the sintering and alloying of the green compact, and a sintered machine component having the required weldability can be economically manufactured. It can be manufactured in a special way.

Claims (14)

[Claims] 1. One of a sintered alloy member and a weldable steel member has a hole or a recess, and the other has a shaft or a projection and has a hole or a recess (hereinafter referred to as an outer member). A weldable sintered machine part formed by fitting and joining a hole of a member having a shaft or a projection (hereinafter referred to as an inner member) and a shaft. 2. One of a member having a hole or a concave portion (hereinafter referred to as an outer member) and a member having a shaft or a projection (hereinafter referred to as an inner member) is formed of a weldable steel material,
The other one is formed of a green compact obtained by compression-molding an iron-based metal powder or a mixed powder of a required composition into a required shape, wherein the outer member and the inner member are formed with respective holes or recesses and shafts or protrusions. Characterized in that sintering of the green compact and joining to the steel material are performed simultaneously by sintering in a state where the components are fitted to each other. 3. A compact having a composition in which the expansion amount in a high temperature region of 800 ° C. or higher is smaller than that of a steel material when the inner member made of a steel material and the outer member of the compact are fitted and sintered. Item 3. A method for producing a weldable sintered machine part according to Item 2. 4. A compact having a composition in which an expansion amount in a high temperature region of 800 ° C. or more is larger than that of a steel material when an outer member made of a steel material and an inner member of the compact are fitted and sintered. Item 3. A method for producing a weldable sintered machine part according to Item 2. 5. The fitting according to claim 3, wherein the fitting dimension difference between the shaft portion of the inner member and the hole portion of the outer member is a fitting with a gap of 5 μm or less or an interference fitting with an interference of 60 μm or less. Manufacturing method of weldable sintered machine parts. 6. The raw material powder constituting the green compact when fitting the inner member made of a steel material and the outer member of the green compact and sintering the raw material is the same as pure iron or steel. A method for manufacturing a weldable sintered mechanical part according to claim 5. 7. The sintering is performed in a non-carburizing atmosphere when the inner member made of steel and the outer member of the compact are fitted and sintered. For manufacturing weldable sintered machine parts. 8. The method according to claim 3, wherein a zinc-free powder lubricant is used for forming the green compact when the inner member made of steel and the outer member of the green compact are fitted and sintered. A method for producing a weldable sintered mechanical part according to claim 6. 9. When the outer member made of a steel material and the inner member of the compact are fitted and sintered, the carbon content of the inner member is set to be 0.2% or more in weight ratio than that of the outer member. Item 6. A method for producing a weldable sintered machine part according to Item 5. 10. When the outer member made of steel and the inner member of the green compact are fitted together and sintered, 2%
The method for producing a weldable sintered mechanical part according to claim 5, wherein said copper is compounded in advance. 11. The manufacture of a weldable sintered machine part according to claim 5, wherein the sintering is performed in a carburizing atmosphere when the outer member made of steel and the inner member of the compact are fitted and sintered. Method. 12. When sintering an outer member made of a steel material and an inner member of a green compact by fitting them together, a powder lubricant containing zinc is used for forming the green compact, and sintering is performed in a carburizing atmosphere. A method for producing a weldable sintered mechanical part according to claim 5, which is performed. 13. The method according to claim 11, wherein the sintering atmosphere is a purified exothermic gas. 14. The method according to claim 13, wherein the sintering atmosphere is a carburizing butane-modified gas.