Microstructure and mechanical properties of selective laser melted 18Ni300 steel

The energy transfer process of selective laser melting (SLM) is highly complex. In this work, experiments were carried out to study the effects of SLM on the microstructure and mechanical properties of 18Ni300 martensitic steel. With the increase in laser power, the grain size of the cladding layer decreases and the microstructure becomes dense. The side hardness is higher than upper surface hardness, and the tensile strength and elongation both increase first and then decrease. When the laser power is 300 W and the scanning speed is 1,000 mm/s, the comprehensive mechanical properties are the best, as the tensile strength, microhardness, elongation at break, and elongation after fracture are 1,217 MPa, 37.5%, 37.6%, and 8.93%, respectively. EBSD (Electron Backscatter Diffraction) shows that columnar crystals grow along the growth direction (z direction) in XOZ and YOZ planes, and the grains show weak texture. There are many small-angle grain boundaries, and the grain sizes are <10 μm.