Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Patent
1985-04-26
1987-06-30
Brody, Christopher W.
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
B22F 100, C22C 3302
Patent
active
046768319
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to iron based powder mixes with low risk of segregation and/or dusting. According to this invention it is now possible to produce mechanical mixes of iron or steel powders and alloying powders with low risk of segregation and dusting without deteriorating the characteristic physical properties of the mixture.
In powder metallurgical manufacturing of various types of components iron or steel powders are often used together with one or more alloying elements such as copper or nickel in order to reach mechanical properties which cannot be obtained when using plain iron or steel powders.
Nowadays powders for these purposes are in general prepared in two ways, viz. either as powder mixtures or as fully prealloyed powders. Powder mixtures are prepared by mixing the iron or steel powder with powder containing the desired alloying element or elements, either in the elementary form or as master alloys. The fully prealloyed steel powders are manufactured e.g. by atomizing a steel melt containing the desired alloying elements to a powder.
One of the drawbacks of powder mixtures is related to the fact that such powders consist of particles which often differ considerably in size, shape and density, and which are not mechanically interconnected. This means that such a powder mixture is susceptible to segregation during its transport and handling. This segregation leads to varying composition of the green compacts manufactured from the powder, and thus to varying dimensional changes during the sintering operation and to varying mechanical properties in the as-sintered product.
Another drawback of powder mixtures is their tendency to dust especially if the alloying element is present in the form of very small particles. This can lead to difficult environmental problems when the powder mixture is handled.
In the case of fully prealloyed powders there is no risk of segregation as every powder particle has the same composition. also the risk of dusting is reduced as no alloying powder having small particle size is included. However, the prealloyed powder has another great drawback, viz. its low compressibility which is a result of the solid solution hardening effect which the alloying elements have on each powder particle. High compressibility is essential when high density is a prerequisite for reaching high mechanical properties.
The compressibility of a powder mixture is on the other hand substantially the same as the compressibility of the iron powder included therein. This fact together with the flexibility as regards the alloying composition have made powder mixtures the most commonly used raw material in the production of low alloy sintered steels. In such powder mixtures the plain iron powder is used as a base powder.
BACKGROUND ART
The Swedish patent application No. 7612217-5 describes a method to produce an iron powder containing copper, which has a low risk of segregation and dusting at the same time as the powder properties are maintained. According to this method the powder is produced by an annealing treatment of a mixture of iron and copper powder, at which a so-called partially diffusion alloy between iron and copper is obtained.
As certain alloying elements, such as e.g. phosphorus in the form of a ferrophosphorus powder and carbon in the form of graphite powder, cannot be sufficiently diffusion alloyed with an iron or steel powder without deteriorating the compressibility, there is a risk that mixtures in which these alloying elements are used are prone to segregation and/or dusting.
The Swedish patent application No. 8001764-3 describes a method to prevent segregation and/or dusting by adding to a powder mixture up to 1% of a sticky binder, which does not change its sticky properties with time at normal temperatures. However, it has been found that when binding agents of this nature are added to a dry powder mix the amount, which can be added, is controlled by the characteristic flowability of the powder mix. The amount which can be used with regard to the
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patent: 2514312 (1950-07-01), Christ
patent: 3583864 (1969-05-01), Adler
patent: 4090868 (1978-05-01), Tengzelius et al.
patent: 4093449 (1978-06-01), Svensson et al.
Mischungs- und Entmischungsprobleme bei Metallpulvern; Teil I: Verhalten von Metallpulvern beim Mischproze.beta.-Makroverteilung der Komponenten; Christa Sauer (Dresden); Jun. 6, 1972, pp. 358-362.
Mischungs- und Entmischungsprobleme bei Metallpulvern; Teil II: Verhalten von Metallpulvern beim Mischproze.beta.-Mikroverteilung der Komponenten; Christa Sauer (Dresden); Apr. 4, 1973, pp. 231-234.
Mischungs- und Entmischungsprobleme bei Metallpulvern; Teil III: Verhalten des Mischguts beim Transport; Christa Sauer (Dresden); Oct. 10, 1973, pp. 595-598.
Brody Christopher W.
Hoganas AB
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