Method of producing a forged article from prealloyed-premixed water atomized ferrous alloy powder

Abstract

A method of making powder metal compacts having a low but optimized alloy content, the compacts being characterized by improved response to heat treatment (hardenability) and improved physical characteristics. A ferrous based powder is prepared having a predetermined particle size (about -80 mesh), a low O.sub.2 content (less than .25%), a predetermined particle shape, less than .04% carbon and balanced pre-alloyed ingredients (.2-1.0% nickel, .2-.8% Mo, and .25-.6% Mn). A nonferrous based powder having at least a high content of copper (-320 mesh if pure copper or about -200 mesh if alloyed copper) is admixed with the prealloyed ferrous based powder to achieve a Cu content of .2-2.1% in the resulting sintered material. Graphite powder is also admixed (.1-1.0% of admixture) to provide a carbon content of at least .17%, but up to .65% in the sintered material; the graphite is preferably a naturally occurring crystalline flake with up to 4.9% max. The admixture is compacted to form a preform having a green density of about 6.4 g/cm.sup.3 and the same weight as the intended forged product but with greater length and reduced width. The preform is ready to be sintered in a low O.sub.2 potential furnace at between 2050.degree.-2500.degree. F and subsequently hot forged at about 1800.degree. F under a force of 50 to 100 tons/in.sup.2. Also disclosed are related methods of making powder ingredients for compacts and the method of carrying the process through the forging stage. Variations of the alloying ingredients in said admixed powders include: (a) employing 0.4-0.65% each of one or all of the alloying ingredients for said prealloyed iron powder, admixing the ferrobased powder with pure copper powder (99.5% pure) in the amount typically about .9% of the mixture, (b) employing a 0.40-0.65 Ni, 0.45-0.65 Mo) prealloyed iron powder with a Cu-Mn powder, (c) employing a Mo prealloyed iron powder admixed with a Cu-Mn-Ni powder or Cu-Mn powder, or (d) employing Mo and Ni in the prealloyed ferrobased powder limited to .19% and employing additional Ni and Mn in a nonferrous based powder having copper to be admixed; graphite powder is added to the admixture in all of the foregoing.

Dependencies are inferred from the claim text.