Ultrahigh strength ferrous sintered components

Compacts made from a newly developed composite-type alloy steel powder with 2%Ni and 1%Mo show superior mechanical properties after heat treatment. The case-hardened compacts exhibit a tensile strength of 1500MPa, absorbed energy of 21J, rotating bend fatigue strength of 460MPa and a compact fatigue strength of 2530MPa. The levels exceed the corresponding values for compacts made from a conventional 4%Ni-0.5%Mo-1.5%Cu steel powder, which are 1380 MPa, K 20J, 410MPa and 2430MPa, respectively. Double-pressed, double-sintered, bright-quenched and tempered compacts made from the new powder posses ultrahigh tensile strength of 1920MPa with high absorbed energy of 35J. The extraodrinary strengthening is attributed to the strain-induced transformation of Ni-rich austenite to martensite. In the sintered and heat-treated compacts made from the new powder, the austenite transforms almost completely to martensite under stress.