Microstructure, hardness, and thermal fatigue behavior of H21 steel processed by laser surface remelting

We investigate the effects of laser surface remelting on the resistance to thermal fatigue of a hot working die steel H21 in this work. Laser treatment was engineered to process samples with several treated morphologies. A dominantly martensitic microstructure, nano-sized carbide and high dislocation density in the treated area, were resulted. The average microhardness of the treated area is ~780 HV. The thermal fatigue resistance of laser-treated samples is notably higher than their as-received counterpart. As the thermal fatigue cycle increases, the microhardness of treated area is reduced and then flatted. Crack initiation and propagation both are hampered by it.