Steel powder and die-lubricated warm compaction for automotive sintered parts with high density and excellent fatigue property

JFE Steel has developed a new powder metallurgical process named die-lubricated warm compaction method for producing high-density sintered parts using premixed steel powder containing only small amount of internal lubricant. In this method, a newly developed spraying equipment precisely controls the amount of lubricant applied over the die wall. The sintered and bright-quenched compacts were prepared by this method using partially alloyed steel powder, KIP SIGMALOY 415S, containing 4 mass% Ni, 1.5 mass% Cu, and 0.5 mass% Mo. They gave a density as high as 7.5 Mg/m 3 and rotating bending fatigue strengths of 450 MPa and 470 MPa with carbon contents of 0.52 mass% and 0.92 mass% respectively. The density and fatigue strength were superior to those obtained by the conventional double-pressing and double-sintering method. Presumably, the fatigue strength was enhanced by increasing the carbon content because the amount of retained austenite was increased.