Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-09-11
2001-12-25
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S246000, C075S255000, C419S011000, C419S038000
Reexamination Certificate
active
06332904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present inventions relate to a mixed powder for powder metallurgy process, an iron base sintered compact made of the same, and a manufacturing method thereof.
2. Description of the Related Art
Different from conventional manufacturing methods such as rolling, forging or casting, in the powder metallurgy process, metal powder of raw material is processed by compressed powder molding, and then sintered to obtain metal products. High melting point metal material such as W and Mo, porous material such as an oil impregnated bearing and a filter, hard-metal or cermet, or other materials that are hard to obtain by conventional melting methods can be manufactured easily using this powder metallurgy process.
In addition, as the powder metallurgy process does not require cutting, the yield rate is increased, and so the dimensional precision is high. Besides, material segregation or aeolotropy, frequent in the melting process, are rare. Provided with such various advantages, several kinds of materials that have been produced by melting process are gradually manufactured by the powder metallurgy process.
Actually, many of sintered compacts manufactured by powder metallurgy process are automobile parts. Besides, iron base sintering materials are largely used for these sintered compacts. For instance, a sintered material made principally from ion powder, by blending with graphite, copper or other micro powder and sintering to improve strength, weather resistance, wear resistance or the like, is well-known. On the other hand, in order to broaden its application domain, toughness and strength are also required, and for this object, material to which Ni, Mo, or other alloy elements are added is also used.
As representative method to obtain high strength iron base sintered compact by powder metallurgy process, premix process and prealloy method are known as basic method. The premix method consists in, first, blending evenly principal component iron powder with another metal powder to prepare mixed powder, then performing compressed powder molding of the same and, thereafter heating and sintering. This method presents an advantage of relatively easy molding, but added powder in iron powder isolates or segregates in the process before the molding, or added metal powder diffuses itself hardly during the sintering. Therefore, this method brings quality problems such as scattering of strength or dimension of sintered compacts.
On the other hand, the prealloy method consists, first, in preparing alloyed steel powder (prealloy type steel powder) wherein Ni, Mo, Cr or other alloy components are solid solved (alloyed) previously in iron, performing compressed powder molding of the same and, thereafter heating and sintering. As alloyed beforehand, the aforementioned inconvenience of the premix method will not occur. Nevertheless, if the prealloy method is adopted, compression density cannot be increased sufficiently during the compressed powder molding, as alloyed steel powder extremely harder than ordinary iron powder, making difficult to obtain high-density sintered compact. Consequently, it is impossible to make the best use of the properties of the concerned alloyed steel.
SUMMARY OF THE INVENTION
Concerning method to prevent segregation in the premix method, a method for depositing graphite powder on iron and steel powder by means of organic binder is disclosed in the Japanese patent applications laid-open S56-136901 published in 1981 and S63-297502 published in 1988. Moreover, a so-called diffusion deposition method for diffusing and depositing other metal powder or mixed powder on iron powder by heat treatment is disclosed in the Japanese Patent Gazette S45-9649 published in 1970 and the Japanese patent laid-open S63-297502 published in 1988. This diffusion deposition method hardly reduces compressibility and uniforms strength or dimensional precision due to segregation. In other words, for diffusion deposition type mixed steel powder, Ni, Cu, Mo or other single metal powder of their alloyed powder is added to iron powder, blended evenly, and the added powder is diffused and deposited on iron powder surface by diffusion processing, and once diffusion deposited, it never segregates.
Iron base sintered parts are largely used as wear resistant parts requiring abrasion resistance, or high strong parts requiring high strength. Among them, as for of wear resistant parts, FeCr, FeMn, FeMo, WC or other powder is added to mother powder of pure iron powder, diffused type steel powder, prealloy type steel powder to prepare a mixed powder, and then this mixed powder is sintered. Thus obtained sintered compacts are used for automobile engine's valve seat, rocker arm chip, cam or the like. However, these added components deploy only an effect to improve the abrasion resistance, and sintered compacts as sintered can not be the to have a remarkable tensile strength, therefore, quenching/annealing, carburizing quenching/annealing or other thermal treatment is generally applied to improve the strength.
On the other hand, as for high strength material, mixed powder wherein Ni powder or Cu powder is added to JIS (Japanese Industrial Standard) SMF4040 or 5040, diffusion deposition type alloyed steel powder (described below) prealloy type steel powder represented by AISI (American Iron and Steel Institute) 4600 or 4100 are used as raw material powder. However, these raw materials as sintered presents, at most, a tensile strength of 75 kgf/mm, and it is necessary to execute heat treatment after the sintering in order to further increase the tensile strength. In addition, as these sintered compacts without heat treatment present not so good abrasion resistance, heat treatment, especially carburizing quenching/annealing is generally performed after the sintering.
Thus obtained sintered compacts are largely used for automobile transmission parts such as synchronization hubs, cam rings of power steering pump, or the like.
Japanese patent applications laid-open H4-350101 published in 1992, H5-295401 and H5-302101 published in 1993 disclose a technology for obtaining a sintered compact presenting high density, high strength and low dimensional discrepancy during sintering by diffusing conveniently alloy components in iron powder through the adjustment of chemical component composition of added mixed powder, in a mixed powder prepared by adding alloyed powder to iron powder. However, in theses methods, the sintering temperature is relatively high, in general, about 1250 to 1350° C. Moreover, in conventional manufacturing method of iron base sintered compact, heat treatment has been required after the sintering in order to obtain necessary mechanical strength. However, the heat treatment also requires cure work to remove generated heat treatment distortion, increasing inevitably the process cost.
The present invention has been devised to solve the aforementioned problems and has an object to provide iron base sintered compact presenting good tensile strength, fatigue strength, abrasion resistance or other mechanical characteristics, without heat treatment, and mixed powder for preparing such sintered compact by powder metallurgy process.
In order to accomplish the object, a first aspect of the present invention provides a mixed powder for powder metallurgy process characterized by comprising prealloy-type steel mother powder containing 1.5 to 4.5 wt % of alloy component, alloyed micro powder and nickel powder.
According to the first aspect, the combination use of premix method and prealloy method for mixing steel mother powder containing partially alloyed components with alloyed micro powder, and for compressed powder molding using mixed powder, allows to compensate conveniently defects of respective methods, suppress material segregation and improve compressibility. Moreover, by mixing Ni sole powder, this Ni diffuses around steel mother powder, accelerate sintering reaction among particles, and increase strength and toughness of sintered compact. As the result, a
Aoki Toshiaki
Fujiki Akira
Marumoto Kazuhiro
Tanaka Hiroyuki
Yoshida Masaki
Mai Ngoclan
McDermott & Will & Emery
Nissan Motor Co,. Ltd.
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