Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1996-11-12
1999-06-29
Jenkins, Daniel J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75255, 419 38, B22F 312, C22C 3302, C22C 3812
Patent
active
059182938
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an iron-based powder for producing components by compacting and sintering. Specifically, the invention concerns powder compositions which are essentially free from nickel and which, when sintered, give components having valuable properties. The components can be used within e.g. the car industry. The invention also concerns a component of this powder produced by powder metallurgy as well as a method of producing such a component by powder metallurgy.
BACKGROUND OF THE INVENTION
Nickel is a relatively common alloying element in iron-based powder compositions in the field of powder metallurgy, and it is generally known that nickel improves the tensile strength of the sintered components produced from iron powders containing up to 8% of nickel. Additionally, nickel promotes sintering, increases the hardenability and also has a favourable effect on the elongation. There is, however, an increasing demand for powders which do not contain nickel since, inter alia, nickel is expensive, gives dusting problems during the processing of the powder, and causes allergic reactions in minor amounts. From an environmental point of view, the use of nickel should thus be avoided.
The problem behind the present invention is thus to find a nickel-free powder composition having, at least in some respects, essentially the same properties as compositions containing nickel.
Alloying systems which are currently commercially used in this context contain Fe--P, Fe--P--C and, to some extent, Fe--Mo--P. The two carbon-free materials have moderate tensile strength and very good ductility. The Fe--P--C system gives higher strength, 450-650 MPa, but lower ductility.
Fe--P--C--Cu--Mo alloys are previously known e.g. from studies presented at the International Powder Metallurgy Conference 7 Toronto, 1984 and the International Powder Metallurgy Conference and Exhibition, Dusseldorf, 1984, which are reported in articles by Lai Ho-Yi, Liu Changxi, and Yin Hongyu.
The first article concerns an investigation of the distribution of phosphorus in sintered iron-base alloys and the question of whether phosphorus segregates into grain boundaries. The purpose of the investigation is to establish the effect of the distribution of phosphorus in a sintered Fe--P--C--Cu--Mo alloy and its effect on the mechanical properties and fracture modes after sintering and heat treatment.
The second article concerns a work whose purpose was to find out whether phosphorus causes temper brittleness in sintered alloys and to study the mechanical properties, the microstructure and the fracture surfaces of Fe--P--C--Cu--Mo alloys after sintering and heat treatment.
Both articles concern alloys whose Mo content is lower than that of the compositions according to the present invention. The main object of the present invention, however, is to provide products which, after both low- and high-temperature sintering, have high tensile strength without any subsequent heat treatment. The problems solved by the present invention are thus different from the problems discussed in the articles.
Patent Publications WO71919582 and 91/18123 (corresponding to Swedish Patent Publication 468 466) concern powder compositions containing Fe, Mo, P and C. Both publications disclose powder compositions which are different from the compositions according to the present invention and which, owing to their different properties, are intended for other purposes.
International Patent Publication WO 91/19582 discloses compositions to be used for the preparation of impact-resistant components, i.e. components having/high impact energy. An important feature of these known compositions is that the carbon content is low, i.e. below 0.1% by weight. Besides, the impact energy indicates the ductility of a material, and an increased ductility is generally accompanied by decreased tensile strength. Accordingly, this publication does not teach how to obtain high tensile strength.
WO 91718123 discloses powder compositions, whose Mo (or W and Mo) content
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Engdahl Per
Lindberg Caroline
Hoganas AB
Jenkins Daniel J.
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