Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1997-05-19
1999-10-19
Jenkins, Daniel J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75255, 419 38, B22F 312, C22C 3302, C22C 3802, C22C 3812
Patent
active
059692766
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, such as high tensile strength. The components can be used in e.g. the car 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.
BACKGROUND
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 made by iron powders containing up to 8% of nickel. Additionally, nickel promotes sintering, increases the hardenability and has a positive influence on the elongation at the same time.
A currently marketed powder, the use of which results in products having properties similar to those obtained with the product according to the present invention, is Distaloy.RTM.AE, which contains 4% by weight nickel.
There is however an increasing demand for powders which do not contain nickel as, for instance, nickel is expensive, creates 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.
SUMMARY OF THE INVENTION
An object of the present invention is thus to provide a nickel-free powder composition having, at least in some respects, essentially the same properties as compositions containing nickel.
A second object is to provide a low-cost, environmentally acceptable material.
A third object is to provide sintered products which after both low and high temperature sintering have tensile strength values superior to those obtained with Distaloy.RTM.AE.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph of tensile strength versus Mo content,
FIG. 2 is a graph of tensile strength versus Mn--Si content;
FIG. 3 is a graph of tensile strength versus C content;
FIG. 4 is a graph of tensile strength versus C content;
FIG. 5 is a bar graph showing tensile strength for different sintering conditions; and
FIG. 6 is a graph of dimensional charge versus sintered density.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, metal powders which, in addition to iron, contain 0.25-2.0% by weight of Mo, 1.2-3.5% by weight of Mn and 0.5-1.75% by weight of Si, 0.2-1.0% by weight of C and up to 2% by weight of impurities exhibit very interesting properties. Thus, tensile strengths up to 1200 MPa can be obtained, when the metal powders according to the invention are compacted and then sintered at high temperatures.
A preferred iron-based powder composition according to the invention contains 0.5-2% by weight of Mo, 1.2-3% by weight of Mn, 0.5-1.5% by weight of Si, 0.3-0.9% by weight of C, and less than 2% by weight of impurities including less than 0.25% by weight of Cu. In addition to Cu, the impurities can consist of Cr, Ni, Al, P, S, O, N, Be, B etc. in amounts less than 0.5% by weight, respectively.
Mo might be used as metal powder, partially pre-alloyed with Fe or prealloyed with Fe. When Mo is added to the iron powder, the hardenability of the compressed material increases and it is recommended that the amount of Mo should be at least 0.25% by weight. As, however, increasing amounts of Mo result in decreased compressibility and, accordingly, decreased density, the amount of Mo should preferably be less than about 2.0% by weight. Furthermore, too high amounts of Mo, especially in combination with high amounts of C, make the sintered material hard and brittle and the strength of the material will decrease.
Mo is preferably added in the form of a prealloyed base powder, which makes it possible to obtain a more homogenous microstructure consisting of bainite and martensite in the sintered material.
Accordi
REFERENCES:
patent: 2797162 (1957-06-01), Korczynsky
Hoganas AB
Jenkins Daniel J.
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