A new phenomenon in a selective laser melted 316L stainless steel with a wider and higher laser energy density

Abstract

Defects, boundaries, textures, tensile properties, fractographies, sub-grains, nano-oxide particles, and deformation twins in selective laser melted 316L stainless steel (SLM316LSS) were systematically characterized as functions of laser energy density. The defects, boundaries, textures of the as-built SLM316LSS were shown to depend largely on the applied laser power. The porosity of the SLM316LSS significantly decreased with the increase laser power from 70 to 140 W (corresponding to the laser energy density from 116.7 to 233.3 J/mm3), while exhibiting a slight increase in the laser power range of 140–280 W (the laser energy density of 233.3–466.7 J/mm3). Additionally, the SLM316LSS specimen at a laser power of 140 W reached the hardness of ∼252 HV, the yield strength of ∼605 MPa and the ultimate tensile strength of ∼710 MPa, along with the elongation to fracture of ∼32.5%, respectively, due to the lowest defect concentration and the presence of twin boundaries and textures, combined with SiO2 nano-oxide particles and deformation twinning. However, the crack appeared in the SLM316LSS within the laser power range from 210 to 280 W (the laser energy density from 350.0 to 466.7 J/mm3), and the mean crystallite size was more than 50 μm, which insignificantly affected the mechanical properties of the steel compared with a laser power of 140 W.