Investigation of different intercritically annealing heat treatment on microstructure and mechanical properties of P/M steels produced from diffusion bonded ferrous powders

In this study, effects of different intercritically annealing heat treatment was investigated on microstructure and mechanical properties of P/M steels produced from diffusion bonded ferrous powders. For this purpose, diffusion bonded Fe-1.7Ni-1.5Cu-0.5Mo alloying powders whose commercial name is DISTALOY AB were used. 0.2 % graphite powders and 0.9 % Amide Wax PM as a lubricant were included to these powders. The mixed powders were cold pressed at 670 MPa with single action mould and then sintered at 1250 ºC temperature for 30 min. After sintering processes, pores and ferritic plus pearlitic microstrutures formed in all specimens. Some of sintered specimens were used for direct intercritically annealed at different temperatures 705 -735 -765 ºC. Step quenching heat treatment cycles at 705 -735 -765 ºC temperatures from 890 °C were applied to some of the sintered specimens. To third group sintered specimens, quenching from 890 °C plus tempering at 180 °C for 2 hr and at 250 °C for 3 hr heat treatments were perfomed.Martensite volume fraction increased with increasing intrecritically annealing temperatures. Also, martensite volume fraction of step quenched specimens was higher than that of direct intercritcally annealed specimens. Yield, tensile and impact strength of intercrtically annealed specimens elevated and elongation decreased with increasing martensite volume fraction. Generally, It was found that many mechanical properties of intercrtically annealed specimens were higher than that of quenched plus tempered specimens.