The mechanical properties of austempered 1.75Ni-1.5Cu-0.5Mo alloyed PM steels

The effects of isothermal annealing on the microstructure and mechanical properties of ferrous based Ni-Cu-Mo-C diffusion alloy powder metallurgy (PM) components were investigated. For this purpose, the powder mixtures were pressed and sintered at 1150 & DEG;C. After full austenitisation at 825 & DEG;C, they were kept isothermally in a neutral salt bath at 450 & DEG;C for 15-120 min. Microhardness (HV 0.01), tensile and impact toughness tests of the samples were carried out at room temperature. The hardness value decreased with increasing austempering time. As a result of the austempering of 120 min, the tensile strength increased by 12.2% and became 460 MPa compared to the heat treatment period of 15 min, and the impact toughness was determined to be 14.3 j.cm-2 with an increase of 21%. Under the conditions in this experimental study, optimum strength and ductility values were obtained with austempering time applied in the range of 90-120 min.