Mechanical Properties and Columnar Grains in a Selective Laser Melting Aisi 316l Stainless Steel

Abstract

Optimizing the columnar grains by adjusting the volumetric energy density can improve mechanical properties of the selective laser melting AISI 316L stainless steel (SLM AISI 316L SS) and expand its application prospects in various aspects. The selective laser melting (SLM) technology with different volumetric energy density was used to prepare AISI 316L SS specimens. When the volumetric energy density of the SLM AISI 316L SS is 145.83 J/mm3, value of the molten pool area reaches a peak of 12,282 μm2, and the tensile strength also reaches a peak of 498.48 MPa. Hardness value of the cellular structures can reach 2.89 GPa. Scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) were used to characterize molten pools of the SLM AISI 316L SS. A fish-scale molten pool and a molten channel alternately appear between different layers. Cellular structure presents a three-dimensional tubular structure. Main elements Fe, Cr, Ni and Mo of the SLM AISI 316L SS are evenly distributed without segregation or agglomeration. Columnar grain is a typical microstructure of the SLM AISI 316L SS, and grow in the molten pool. Due to the heat conduction effect, columnar grains grow along nucleation point at boundary of the last secondary molten pool against the temperature gradient. Columnar grains and molten pool boundary play a key role in the strengthening of the SLM AISI 316L SS.

Keywords: Selection laser melting, Mechanical property, Molten pool, Columnar grain, Strengthening mechanism