Microstructure, tensile properties and mechanical anisotropy of selective laser melted 304L stainless steel

The microstructure and mechanical properties of 304 L stainless steel fabricated by selective laser melting are investigated in this study. With the optimized laser processing parameters, a relative density of 99.9 % is achieved with fine austenite grains and nanoscale cellular subgrains in size of approximately 0.5 μm. The presence of δ-ferrite and σ phase precipitates is identified by the x-ray diffraction and transmission electron microscopy. Moreover, the microstructure is identified as an austenite matrix with about 4 % δ ferrite and a trace amount of σ phase by using electron backscattered diffraction analysis. These small σ phase particles are mainly distributed along austenite grain boundaries. Furthermore, the presence of nanoscale cellular subgrains contributes to the good tensile strength and ductility of the selective laser melted 304 L, along with precipitate strengthening and strain hardening. Tensile property anisotropy is also identified in this 304 L, which is attributed to the microstructure difference on vertical and horizontal planes.