Abstract: The microstructure evolution and mechanical properties of laser additive manufactured 316L stainless steel after annealing process were studied by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and tensile testing machine. The results show that after annealing at 700 ℃, the morphology of the fish-scale molten pool begins to gradually transform into an irregular strip shape as the temperature increases. After annealing at 750 ℃, the cellular and long columnar substructures in the molten pool transform into spherical substructure and triangular point-like pit-shaped microstructure. As the annealing temperature increases, the grain size first decreases and then increases, the dislocation density is reordered, the cellular substructure is dissolved, and the evolution of the substructure and large and small angle grain boundaries reflects the decrease in dislocation density, leading to decrease in strength and enhancement in plasticity. When the annealing at 600 ℃ for 120 min, the yield strength is 484.2 MPa, the tensile strength is 665.6 MPa, and the elongation is 47.7%. When annealing at 850 ℃ for 120 min, the yield strength is 410.4 MPa, the tensile strength is 639.1 MPa, and the elongation is 59.7%. As the holding time increases, the deformation zone transforms into substructure; when the holding time is increased from 30 min to 120 min at temperature of 650 ℃, the substructure increases from 24.1% to 82.3%; when the holding time is increased from 30 min to 120 min at temperature of 850 ℃, the substructure is increased from 24.9% to 59.2%.

Key words: laser additive manufacturing(LAM), 316L stainless steel, annealing, microstructure, mechanical properties