Production method for sintered machine components

Abstract

A production method for sintered machine components, includes preparing an Fe alloy powder A, an Fe alloy powder B, an Fe—P powder, and a graphite powder. The Fe alloy powder A consists of, by mass %, 25 to 45% of Cr, 1.0 to 3.0% of Mo, 1.0 to 3.0% of Si, 0.5 to 1.5% of C, and the balance of Fe and inevitable impurities. The Fe alloy powder B consists of, by mass 15 to 35% of Cr, 15 to 30% of Ni, and the balance of Fe and inevitable impurities, and the Fe—P powder consists of 10 to 30 mass % of P and the balance of Fe and inevitable impurities. The production method further includes mixing 40 to 60 mass % of the Fe alloy powder B, 1.0 to 5.0 mass % of the Fe—P powder, and 0.5 to 3.5 mass % of the graphite powder with the Fe alloy powder A into a mixed powder. The production method further includes compacting the mixed powder into a green compact and sintering the green compact.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]The present invention relates to a production method for sintered machine components; the production method may be preferably used for, for example, turbo components of turbochargers, and specifically, nozzle bodies that must have heat resistance, corrosion resistance, and wear resistance.[0003]2. Background Art[0004]In general, in a turbocharger fixed to an internal combustion engine, a turbine is rotatably supported by a turbine housing connected to an exhaust manifold of the internal combustion engine, and plural nozzle vanes are rotatably supported such that the nozzle vanes surround the outer circumference of the turbine. Exhaust gas flowing in the turbine housing flows from the outer circumference of the turbine into the turbine and is discharged in the axial direction, thereby rotating the turbine. A compressor is provided at the same shaft as the shaft of the turbine and is at a side opposite to the side with the nozzl...

AI Technical Summary

Benefits of technology

[0009]In the production method for sintered machine components of the present invention, the Fe alloy powder A includes a substantial amount of elements for improving wear resistance, and the Fe alloy powder B is soft and improves compressibility of the Fe alloy powder A. The alloying elements are divided into the Fe alloy powder A and the Fe alloy powder B and are added together, whereby compressibility of the raw powder is improved. In order to densify the sintered compact, the liquefying temperature of the mixed powder of the Fe alloy powder A and the Fe alloy powder B is reduced so that a liquid state is generated in sintering. Therefore, P and C are used in the form of an Fe—P powder and the graphite powder, respectively, and the Fe—P powder and the graphite powder are mixed with the Fe alloy powder A and the Fe alloy powder B, whereby a mixed powder is formed. Hereinafter, the reasons for limiting the above amounts and functions of the present invention are described. In the following descriptions, the symbol “%” represents “mass %”.Cr:

[0010]Cr improves heat resistance and corrosion resistance of a matrix, and Cr also improves wear resistance when combined with C into carbides. In order to uniformly improve a matrix by such effects of Cr, Cr is added to the mixed powder in the form of an Fe alloy powder. If the amount of Cr in the Fe alloy powder A is less than 25%, and the amount of Cr in the Fe alloy powder B is less than 15%, precipitation amount of Cr carbides is small, whereby wear resistance will be insufficient, and heat resistance and corrosion resistance of a matrix are decreased. On the other hand, if the amount of Cr in the Fe alloy powder A is more than 45%, the compressibility of the raw powder is extremely decreased. Therefore, the upper limit of the amount of Cr in the Fe alloy powder A must be 45%. In order to form the Fe alloy powder B so that it is soft, the upper limit of the amount of Cr in the Fe alloy powder B must be 35%. Accordingly, the amount of Cr in the Fe alloy powder A is set to be 25 to 45%, and the amount of Cr in the Fe alloy powder B is set to be 15 to 35%. Since the Fe alloy powder B must be softer than the Fe alloy powder A, the amount of Cr in the Fe alloy powder B must be less than the amount of Cr in the Fe alloy powder A.Mo:

[0016]C can lower a liquefying temperature, thereby generating an Fe—P—C liquid phase in sintering and facilitating densification of a sintered compact. In addition, C improves wear resistance when combined with Cr or Mo into carbides. In a case of adding the entire amount of C in the form of a graphite powder, an Fe alloy powder includes Cr and Mo that are solid solved in the Fe matrix, and the Fe alloy powder is too hard, whereby the compressibility of the Fe alloy powder is decreased. Use of a large amount of the graphite powder also causes decrease in the compressibility of the mixed powder. Therefore, a partial amount of C is added to the mixed powder in the form of an Fe alloy powder, and the remaining amount of C is added to the mixed powder in the form of a graphite powder. In this case, since the Fe alloy powder B must be soft, a partial amount of C is added to and is solid solved in the Fe alloy powder A. When a partial amount of C is added to the mixed powder in the form of an Fe alloy powder A, Cr and Mo in the Fe alloy powder A precipitate in the Fe alloy powder A as carbides, whereby the amounts of Cr and Mo solid solved in the matrix of the Fe alloy powder A are decreased, and the compressibility of the Fe alloy powder A is improved. Moreover, by adding the remaining amount of C to the mixed powder in the form of a graphite powder, the compressibility of the mixed powder is improved. If the amount of C in the Fe alloy powder A is less than 0.5%, the amounts of Cr and Mo solid solved in the Fe alloy powder A are increased, whereby the hardness of the Fe alloy powder A is increased, and the compressibility of the Fe alloy powder A is decreased. On the other hand, when the amount of Cr is more than 1.5%, the amount of carbides precipitated in the Fe alloy powder A is too great, whereby the hardness of the Fe alloy powder A is increased. Therefore, the amount of C in the Fe alloy powder A is set to be 0.5 to 1.5%.

[0021]According to the production method for sintered machine components of the present invention, heat resistance, corrosion resistance, wear resistance, and high-temperature strength can be improved, and a sintered machine component having a thermal expansion coefficient equivalent to that of an austenitic heat-resistant steel is obtained.

Problems solved by technology

In this case, the turbo component has a different thermal expansion coefficient from that of surrounding members, whereby the design of the turbo component is difficult for practical use.

If the amount of Cr in the Fe alloy powder A is less than 25%, and the amount of Cr in the Fe alloy powder B is less than 15%, precipitation amount of Cr carbides is small, whereby wear resistance will be insufficient, and heat resistance and corrosion resistance of a matrix are decreased.

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