JPH05302101A - Mixed powder for powder metallurgy/and its sintered compact - Google Patents

Abstract

PURPOSE:To provide a mixed powder for powder metallurgy capable of obtaining a high-density, high-strength and uniform sintered compact mainly by the premix method. CONSTITUTION:Iron powder and an alloy powder are mixed to obtain a mixed powder for powder metallurgy. The mixed powder contains Ni, Mo and B as the essential components. A sintered compact having desired characteristics is obtained by using such a mixed powder.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a powder mixture for powder metallurgy, which is based on iron powder and alloy powder and is capable of obtaining a sintered body having high density and high strength and less variation in characteristics. The present invention relates to such a sintered body.

[0002]

2. Description of the Related Art The powder metallurgy method is a method in which a conventional production process including rolling, forging, casting, etc. is largely rewritten, and a metal powder as a raw material is compression-molded and then sintered to obtain a product. Therefore, according to the powder metallurgy method, it is difficult to manufacture by the conventional melting method such as high melting point metal materials such as W and Mo, porous materials such as oil-impregnated bearings and filters, cemented carbide and cermet. Can be manufactured. Not only that, but in the case of ingots such as the improvement in material yield due to non-cutting, advantages in manufacturing such as high dimensional accuracy, and the advantage in terms of material with less segregation and anisotropy that are likely to occur in ingots. Since there are various advantages that cannot be obtained, various members conventionally manufactured by the melting method are replaced with the powder metallurgy method and manufactured.

Most of the sintered bodies manufactured by powder metallurgy at present are used as parts for automobiles, and iron-based sintered members are especially widely used. Various types of such iron-based sintered members are known, and for the purpose of improving strength, weather resistance, wear resistance, etc., graphite or copper is used as the main component of iron powder. It is known that fine powders such as the above are mixed and sintered. Further, from the viewpoint of expanding the range of application of sintered members, higher toughness and strength are required for sintered members, and alloying elements such as Ni and Mo are added to form alloys as a means for achieving the toughness and strength. It is also known how to do it.

The premix method and the prealloy method are known as typical methods for obtaining a high-strength iron-based sintered body by the powder metallurgy method.

The premix method is a method in which iron powder and other metal powders or alloy powders (hereinafter sometimes referred to as additive metal powders) are uniformly mixed, the powders are compacted, and then heated and sintered. .. This method has the advantage that the forming process is relatively simple, but the additive metal powder in the iron powder is separated / segregated due to the difference in specific gravity in the stage up to powder compaction, or the additive metal is added during sintering. There is a problem in that the diffusion of powder does not proceed sufficiently, and there is a quality problem in that the strength and dimensions of the sintered body vary.

On the other hand, the pre-alloy method uses Ni, Mo,
Since alloy steel powder in which an alloying element such as Cr is dissolved in iron in advance is used, the problem as pointed out in the premix method does not occur. However, in this method, the alloy steel powder obtained by pre-alloying is much harder than iron,
It is not possible to sufficiently increase the compaction during powder compaction, and it is difficult to obtain a high-density sintered body. Therefore, the physical properties of the alloy steel cannot be fully utilized.

Although each of the above methods has advantages and disadvantages, the premix method is preferable to the prealloy method if the problems such as the occurrence of segregation and the insufficient diffusion as described above can be overcome. It is considered to be advantageous in obtaining a sintered body.

As a means for preventing segregation, a method of adhering graphite powder to iron / steel powder using an organic binder is proposed, as disclosed in, for example, JP-A-56-136901 and 63-103001. Has been done. Further, for example, Japanese Patent Publication No. 45-9649 and Japanese Patent Laid-Open No. 63-297.
As disclosed in No. 502, a so-called diffusion adhesion method has also been developed in which other metal powder or alloy powder is diffusely adhered to iron powder by heat treatment. In particular, the diffusion adhesion method hardly reduces the compressibility and can prevent the problem of uneven strength and dimensional accuracy due to segregation to some extent. That is, the diffusion-adhesive alloy steel powder is obtained by adding elemental metal powders such as Ni, Cu, Mo, etc. or their alloy powders to iron powder and mixing them uniformly, followed by diffusion treatment to diffuse the additive metal powder on the iron powder surface. It is to be adhered, and segregation does not occur for those once diffused and adhered.

[0009]

SUMMARY OF THE INVENTION The present invention has been made based on such a technical background, and focuses on a premix method, and by this method, sintering having high density, high strength and uniform physical properties is performed. An object of the present invention is to provide a mixed powder for powder metallurgy capable of obtaining a body, and a sintered body having such characteristics.

[0010]

The constitution of the present invention which has been able to solve the above-mentioned problems is a mixed powder for powder metallurgy, which is obtained by mixing iron powder and alloy powder, wherein the alloy powder is N
The gist is that it contains i, Mo and B as essential components.

It is also effective to contain a small amount of Al or Ti as the alloy powder. These elements not only lower the melting point of the alloy powder to improve the diffusivity, but also prevent the oxidation of B during sintering. Is also effective.

Further, it is also effective to make the alloy powder contain at least one selected from the group consisting of Cu, Mn, Si and Cr, and these elements contribute to the improvement of the strength of the sintered body.

By sintering the mixed powder composed of the above-mentioned components, it is possible to obtain a sintered body having a high density and a high strength and less variation in dimensional accuracy during sintering.

[0014]

The present inventor has conducted various studies from the viewpoint of improving the diffusivity of the alloy powder with respect to the iron powder. As a result, the addition of a small amount of B to the alloy powder lowers the melting point of the alloy powder and causes the diffusion of the alloy powder. Of the resulting sintered body
The inventors have found that high strength can be achieved and completed the present invention.

In the present invention, it is important that the additive elements such as Ni and Mo are not in the form of a single metal powder but are used as a pre-alloyed powder. That is, Ni,
Elementary elements for alloys such as Mo have a high melting point and have a slow diffusion rate into iron powder. However, by alloying these elements in advance, the melting point is lowered compared with the case of an elemental powder, and diffusibility into iron powder is improved. To improve the strength of the sintered body.

The use of alloy powder is also effective from the viewpoint of obtaining a sintered body having uniform characteristics.
That is, the mixed powder of the present invention is (1) mixed as it is with other auxiliary materials and sintered, (2) a powder obtained by previously adhering iron powder and alloy powder by a binder or diffusion treatment, and then It can be used in any procedure such as mixing and sintering the auxiliary raw materials of 1., but whichever procedure is adopted, a sintering powder having a microscopically uniform alloy component ratio can be obtained. Therefore, the properties of the powder become constant, and the properties of the obtained sintered body also become uniform. In particular, when it is used as a diffusion-adhesive powder, the above effect is remarkably produced when it is used in the form of alloying powder as compared with the form of a single metal powder.

The mixed powder of the present invention can be used in the form of either a binder-adhesive powder or a diffusion-adhesive powder as described above. However, in the case of a diffusion-adhesive powder, the subsequent sintering treatment results in two stages. Since the same treatment as the annealing is performed, it is preferable from the viewpoint of improving the strength.

Next, the components of the alloy powder used in the present invention will be described. Ni is an element that improves toughness and hardenability, and Mo enhances hardenability and prevents softening during quenching and tempering.

In the case of Ni-Mo system, 50% (% by weight)
Has the eutectic point near Mo, and the high melting point of Mo can be lowered by adopting the Ni-Mo system, which facilitates diffusivity into iron powder, that is, uniform alloying. Becomes However, when Mo exceeds 50%, the liquidus temperature rises sharply, and the melting point lowering effect is almost eliminated. Therefore, the addition amount of Mo is preferably equal to or less than that of Ni. In addition, the content of Ni and Mo is preferably about 1 to 12% in total with respect to the iron powder, and when it is more than this, the amount of iron powder becomes relatively small, which is the basis for the iron powder-based sintered body. The sinterability, which is a required property, is reduced.

As described above, the addition of B lowers the melting point of the alloy powder and significantly improves the diffusivity of the alloy powder. Such an effect is exhibited at about 0.2% or more with respect to the total amount of Ni and Mo. However, if too much is added, the liquid phase is remarkably generated, hexagonal recrystallized Fe particles grow, and Mo borides are generated at the grain boundaries, which may cause grain boundary embrittlement. Therefore, the addition amount of B should be suppressed to about 2% with respect to the total amount of Ni and Mo.

In addition to the above components, addition of a small amount of Al or Ti is also effective for lowering the melting point of the alloy powder and preventing B oxidation. However, if too large, oxide-based inclusions are generated, so the amount of these elements added should be up to three times the amount of B added.

It is also effective to add one or more elements selected from the group consisting of Cu, Mn, Si and Cr from the viewpoint of improving strength, but if too much, the action of the basic components is reduced. From Ni and Mo
It is not preferable to exceed the total amount of

Considering only the lowering of the melting point, it can be expected that the addition of elements such as P and Sn is also effective, but with these elements, the carburizing expansion of graphite and the appearance of the liquid phase are overlapped during sintering, which causes a remarkable expansion. Moreover, the strength is greatly reduced, which is not preferable.

[0024]

[Examples] Iron powder-6% alloy powder-0.6% graphite-0.75% zinc stearate-based mixed powder was compacted at 6 ton / cm ² and then sintered at 1250 ° C. in a hydrogen atmosphere to obtain The tensile strength of the obtained sintered body was investigated. The alloy powder used had an average particle size of about 12 μm produced by a water atomization method and 70% Ni
Based on the composition of -15% Cu-15% Mo, Al and Ti are each contained in an amount of 1% and various proportions of B are contained.

FIG. 1 shows the relationship between the B content (vs. Ni + Cu) and the tensile strength. As is clear from FIG. 1, addition of up to about 2% of B is effective for improving the strength of the sintered body. However, the addition of B in excess of 2% has lower strength than the sintered body of the basic component.

FIG. 2 shows the alloy powder of the above-mentioned basic components, and 0.5% B, 1% Al and 1% T based on the basic components.
It is a graph which shows the result of the differential thermal analysis of the alloy powder containing i. It can be seen that the generation of the liquid phase occurs at 1322 ° C and 1232 ° C, respectively. Therefore, the sintering temperature is, for example, 12
In the case of 50 ° C, the alloying elements of the basic components are solid phase diffused into the iron powder and the diffusion is slowed, while the liquid phase appears in the alloys containing B, so that the diffusion to the iron powder is caused. Will progress promptly.

FIG. 3 is a graph showing the influence of the alloy powder composition on the tensile strength of the sintered body. In the case where (A) 0.5% B was added to various basic components, (B) 0.5% B, 1
The graphs show the changes in strength in the case of containing 2% Al and 1% Ti in comparison. The manufacturing conditions were the same as those described above.

As is apparent from FIG. 3, addition of B, Al, Ti, etc. is extremely effective for improving strength in any alloy composition.

[0029]

EFFECTS OF THE INVENTION The present invention is configured as described above, and by using a powder mixed with iron powder in a form containing B as an essential component and being alloyed, a high density, high strength and uniform A characteristic sintered body could be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the tensile strength of a sintered body and the B content.

FIG. 2 is a graph showing the results of differential thermal analysis of various alloy powders.

FIG. 3 is a graph showing the influence of alloy powder composition on the tensile strength of a sintered body.

Claims (4)

[Claims] 1. A mixed powder for powder metallurgy, comprising a mixture of iron powder and an alloy powder, wherein the alloy powder contains Ni, Mo and B as essential components. .. 2. A sintered body obtained by sintering using the mixed powder according to claim 1. 3. A mixed powder for powder metallurgy, which is a mixture of iron powder and alloy powder, wherein the alloy powder contains Ni, Mo and B as essential components, and is selected from the group consisting of Al and Ti. A mixed powder for powder metallurgy, comprising one or more kinds, and further one or more kinds selected from the group consisting of Cu, Mn, Si and Cr, respectively. 4. A sintered body obtained by sintering using the mixed powder according to claim 3.