Effect of Thermal Fatigue on Microstructure and Mechanical Properties of H13 Tool Steel Processed by Selective Laser Surface Melting

Selective laser surface melting, which brings together the bionic theory and the laser process, is an effective way to enhance the thermal fatigue behavior of materials. In this study, in order to examine the relationship between the mechanical properties and thermal fatigue behavior of materials processed by selective laser surface melting, the tensile properties at room temperature and elevated temperature of treated specimens and untreated specimens after different numbers of thermal fatigue cycles were investigated and compared. Moreover, the microstructure evolution and the microhardness of the laser-affected zone were investigated after different numbers of thermal fatigue cycles. The results show that microhardness of the laser-melted zone gradually decreases with an increasing number of thermal fatigue cycles; the number of thermal fatigue cycles has little effect on the grain size in the laser-melted zone, and the percentage of low-angle grain boundaries decreases with an increasing number of thermal fatigue cycles. The strength of specimens gradually decreases, whereas the fracture elongation gradually increases with an increasing number of thermal fatigue cycles at room temperature and elevated temperature. In addition, the stress distribution on the specimen surface during tensile test was investigated using the finite element method, and the results indicate that the stress transfer exists between the laser-affected zone and the untreated zone.