Microstructure and tensile properties of selective laser melting forming 316L stainless steel

The selective laser melting technology shows great advantages in the field of manufacturing of complex parts, but the organization and the comprehensive performance of the specimens have yet to be further optimized. Specimens of 316L stainless steel were fabricated by selective laser melting technology, the microstructure characteristics of different regions were analyzed, the tensile mechanical properties were tested. The results showed that the micro-structure were mainly cell crystal. However, the grain growth direction were different in some "micro-melting pools", and almost perpendicular to each other, which showed a small typical columnar crystal in the same field of view (subgrain) and "hexagonal cellular crystal" coexistence of micro-structure characteristics. Compared with the traditional specimens, the tensile strength of had greatly improved, but the elongation decreased. This was mainly due to the fact that SLM was a process of rapid melting and solidification which maked the difference of laser incident angle, scanning strategy and heat dissipation conditions resulting in complex crystals at different regions and different microstructure. The fine columnar crystal formed by rapid cooling that was submicron order and densely distribute was the main reason of the increases in tensile strength. However, the obvious anisotropy of grain, which resulted in the uneven deformation of grain in different directions and restrained mutually during the tensile test, and the inevitable remarkable internal stress at the interface of fusion lines leaded to a decrease in elongation.