Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1997-02-06
1997-12-30
Jenkins, Daniel J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75246, 75252, 419 11, 419 38, 419 46, B22F 312, C22C 124, C22C 125
Patent
active
057033048
DESCRIPTION:
BRIEF SUMMARY
The present invention is related 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, such as high tensile strength. The components can be used within e.g. the automotive industry. The invention also concerns a powder-metallurgically produced component of this powder as well as a method of powder-metallurgically producing such a component.
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 which have been produced by iron powders containing up to 8% of nickel. Additionally, nickel promotes sintering, increases the hardenability and has positive influence on the elongation at the same time. There is, however, an increasing demand of powders which do not contain nickel as i.a. nickel is expensive, gives dusting problems during the processing of the powder, 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 connection contain Fe--Cu--C and to some extent Fe--Mo--Cu--C. These two materials have a relatively high tensile strength (400-700 MPa). High tensile tent Fe--Mo--Cu--C. These two materials have a relatively high tensile strength (400-700 MPa). High tensile strength (>700 MPa) can be obtained with Fe--Mo--Cu--C material after sintering in furnaces, in which convective cooling can be used. The development of the compositions according to the present invention has quite unexpectedly made it possible to increase the tensile strength to values above 800 MPa also without convective cooling.
According to the present invention metal powders which, in addition to iron, essentially consist of 0.7-2.0% of Mo, 0.2-2.5% by weight of Cr and 0-3.0% by weight of Cu, 0.05-0.25% by weight of Mn and 0.3-1.0% by weight of C, wherein Fe, Mo and Mn are present as a prealloyed, water atomised FeMoMn base powder, Cr is present as FeCr, Cu is present as a metal powder or partially prealloyed to the above mentioned base powder exhibit very interesting properties. Thus, tensile strengths above 650 MPa can be obtained, when the metal powders according to the invention are pressed and then sintered at high temperatures.
Metal powders including Fe, Mo, Mn, Cr and C are previously known from i.a. the Japanese patent publication JP-A-61-276 949. This publication concerns an invention, which is intended to solve problems with heat treated products having insufficient surface hardness or strength after nitriding. The problems are solved by the manufacture of a green body including 0.5-6.0% Cr, 0.2-0.6% C and at least one of 0.3-1.5% by weight Mn, 0.1-2.0% by weight of Mo, 0.2-2.0% by weight of Cu and 0.2-3.0% by weight of Ni, the rest being Fe, which body is sintered and then subjected to a nitriding treatment. The green body is made from a completely pre-alloyed powder or from mixing FeCr, FeMn, Cu, Mo, Ni and other powders into a pure iron-powder. The present invention concerns quite another problem, namely to provide nickel-free products which, when sintered, are distinguished by e.g. high tensile strength. The known powders differ from the powders according to the present invention i.a. as regards the Mn-content, which according to the present invention should be between 0.05 and 0.25%, whereas in the known powder, if present, Mn should be in the range of 0.3 to 1.5%. The lower Mn content according to the present invention is of importance to avoid oxidation during water atomisation and to keep good compressibility of the powder. Additionally, in the actual examples of
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Engdahl Per
Lindberg Caroline
Hoganas AB
Jenkins Daniel J.
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