STRENGTHENING MECHANISM OF SINTERED AND H EAT-TREATED COMPACTS MADE FROM PARTIALLY PREALLOYED STEEL POWDERS

Extensive study has been executed for an optimization of chemistry of partially prealloyed steel powders with Ni and Mo for the production o f high strength and high toughness sintered components via double-pres sing, double-sintering and heat treatment. The austenite precipitates at Ni-rich phases in the sintered and heat-treated compacts made from partially prealloyed steel powders with 0.6% graphite. The detailed an alysis of stress-strain curve of sintered and heat-treated compact ind icates that deformation is localized at untransformed austenite and st rain induced martensite with very high strength is formed at the initi al stage. The tensile strength increases with the amount of strain ind uced martensite. Condensed carbon areas are observed in the specimen w ith higher amount of austenite. The tensile strength depends also on t he carbon concentration in martensite. The maximum tensile strength in creases with the decrease of Ni content. This is attributed to the dec rease of sintered density and the increase of untransformed austenite for plastic deformation. The sintered and heat-treated compacts made f rom the 2%Ni-1%Mo steel powder contain a sufficient amount of austenit e which transform almost completely to martensite during loading. Ther efore, this compact shows an ultra high strength of 1920MPa and a high unnotched Charpy absorbed energy of 53J.