Subgrain Microstructures and Tensile Properties of 316L Stainless Steel Manufactured by Selective Laser Melting

316L stainless steel samples were manufactured by selective laser melting (SLM). The microstructure of SLM-made 316L stainless steel and the room temperature tensile properties both perpendicular and along the building direction were studied and characterized. The static temperature field during the molten pool formation was simulated by finite element simulation. It indicates that the nonlinear asymmetrical inclined temperature gradient in SLM process produces a large surface tension gradient. The melt forms a Marangoni flow with different convection modes under the action of surface tension as well as a micro-molten pool morphology with subgrain structures such as strip, hexagonal and elongated cellular structures. In addition, there are also epitaxially grown columnar grains. The growth of columnar crystals is not affected by the boundary of the molten pool. Subgrain structures and low-angle grain boundaries make the tensile strength and the elongation of SLM-made 316L sample higher as compared to those of the cast and wrought samples. The room temperature tensile strength of the sample perpendicular to the building direction is higher than that of the sample along the building direction, while the elongation is lower than that of the sample along the building direction.