Abstract: A powder metal material comprises pre-alloyed iron-based powder including carbon present in an amount of 0.25 to 1.50% by weight of the pre-alloyed iron-based powder. Graphite is admixed in an amount of 0.25 to 1.50% by weight of the powder metal material. The admixed graphite includes particles finer than 200 mesh in an amount greater than 90.0% by weight of the admixed graphite. Molybdenum disulfide is admixed in an amount of 0.1 to 4.0% by weight of the powder metal material, copper is admixed in an amount of 1.0 to 5.0% by weight of the powder metal material, and the material is free of phosphorous. The powder metal material is then compacted and sintered at a temperature of 1030 to 1150° C. At least 50% of the admixed graphite of the starting powder metal material remains as free graphite after sintering.

Abstract: A most preferred composition for the mixture, prior to sintering into an article (ideally a valve seat insert), is as follows: 35% hard phase, 65% matrix (excepting incidental impurities), the hard phase component being 2.2% C, 29.1% Cr, 4.9% Co, 5.3% Ni, 20.2% W with the balance being Fe and allowing less than 2% for one or more machinability aids and solid lubricants, and the matrix component being one of a high chrome steel powder (e.g. 18% Cr, 1% Ni, 2.5% Mo, balance Fe), a low alloy steel powder (3% Cu, 1% C, balance Fe; 3% Cr, 0.5% Mo, 1% C, balance Fe; 4% Ni, 1.5% Cu, 0.5% Mo, 1% C, balance Fe; 4% Ni, 2% Cu, 1.4% Mo, 1% C, balance Fe), or a tool steel powder (5% Mo, 6% W, 4% Cr, 2% V, 1% C, balance Fe), or a low-alloy steel powder as above but which issued in conjunction with a copper infiltration process during sintering.

Abstract: A powder metal steel alloy composition for high wear and temperature applications is made by water atomizing a molten steel alloy composition containing C in an amount of at least 3.0 wt %; at least one carbide-forming alloy element selected from the group consisting of: Cr, V, Mo or W; an O content less than about 0.5 wt %, and the balance comprising essentially Fe apart from incidental impurities. The high carbon content reduces the solubility of oxygen in the melt and thus lowers the oxygen content to a level below which would cause the carbide-forming element(s) to oxidixe during water atomization. The alloy elements are thus not tied up as oxides and are available to rapidly and readily form carbides in a subsequent sintering stage. The carbon, present in excess, is also available for diffusing into one or more other admixed powders that may be added to the prealloyed powder during sintering to control microstructure and properties of the final part.

Abstract: A method of making a sintered article is disclosed, the method comprising the steps of mixing a prealloyed ferrous powder having a composition in the following ranges in weight %: carbon 0.7-2.7/chromium 3-6/cobalt 5-10/vanadium 0.5-3/molybdenum 6-11/silicon 0.3-2/ others total 2 max/balance iron and optionally up to 3 wt % tungsten, with an addition of carbon powder of at least 0.1 wt %, compacting said powder mixture by uniaxial pressing to form a green compact of near net shape, sintering said green compact in a continuous gas atmosphere sintering furnace at a temperature in the range from 1130.degree. C. to 1250.degree. C. such that the final density of said sintered material is greater than 95% of the theoretical density as a result of the sintering operation alone.