Effect of different sintering temperatures and atmospheres on the microstructure and mechanical properties of particulate M2 high-speed steel

The present work investigates the effects of sintering temperatures and different sintering atmospheres on M2 high-speed steel. It is well known from the pseudo-binary phase diagram that, with an increase in temperature from 1250 ºC to 1350ºC, the sintering process changes from solid-state sintering to super-solidus liquid-phase sintering, resulting in increased densification with increasing sintering temperature owing to enhanced sintering kinetics and liquid formation. The carbide particle size also increases with increasing sintering temperature, resulting in coarser carbide and the formation of a carbide network at higher temperatures. It has been observed that densification increases in H2 atmosphere to ~99% compared to N2 (81%) and Ar (93%). Furthermore, carbide forms more finely in an N2 atmosphere, but it has a higher pore density. In the H2 atmosphere, coarse carbides are uniformly distributed in the alloy; moreover, a coarse carbide network is detected in the Ar atmosphere. Furthermore, increasing the sintering temperature from 1250ºC to 1350ºC results in a rise in bulk hardness from 119 HV0.2 to 239 HV0.2. However, Bulk hardness is also improved in the H2 atmosphere to 453 HV0.2 sintered at 1300ºC.