Heat treatment influence on the microstructure and mechanical properties of NM500 wear resistant steel

The effects of direct quenching-tempering (DQ-T) and reheat quenching-tempering (RQ-T) on the microstructure and mechanical properties of NM500 wear resistant steel were studied by scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy, and mechanical testing. The strengthening mecha-nisms of these heat treatment processes were also discussed in the paper. It is found that samples treated by DQ-T and RQ-T both have good ductility and high strength. The tensile strength and hardness of the DQ-T sample are superior to those of the RQ-T sample due to higher densities of dislocations and smaller sizes of martensite blocks, but the impact toughness and ductility of the DQ-T sample do not drop significantly. For the RQ-T sample, reheat quenching temperature has a remarkable effect on the strength, and fine blocks can be obtained when the quenching temperature is not high. This grain refinement strengthening can be an effective method to increase the strength of the RQ-T sample.