Effects of heat treatment process regulation on mechanical properties and microstructure of laser powder bed fusion 316H stainless steel

Abstract

316H stainless steel fabricated by laser powder bed fusion (LPBF) usually exhibits high strength but limited ductility due to the rapid solidification characteristics and heterogeneous as-built microstructure. In this work, the effects of solution heat treatment on the tensile properties, phase constitution, and microstructural evolution of LPBF-produced 316H stainless steel were systematically investigated. An L9(32) orthogonal experimental design was adopted, with solution temperatures of 1050, 1100, and 1150 °C and holding times of 1, 2, and 4 h. Room-temperature tensile tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to characterize the mechanical behavior and underlying microstructural changes. The results show that all solution-treated samples retained a single austenitic phase without detectable δ-ferrite or harmful precipitates. Compared with the as-built condition, solution treatment led to a reduction in tensile and yield strengths but a significant increase in elongation. Among the tested conditions, 1100 °C for 2 h provided the best balance between strength and ductility, with an ultimate tensile strength of 597.01 MPa, yield strength of 265.33 MPa, and elongation of 53.83%. The improvement in ductility is mainly attributed to the transformation from directional columnar grains to homogeneous equiaxed grains, the reduction of residual strain, and the substantial increase in the fraction of high-angle grain boundaries. These findings provide useful guidance for tailoring the strength-ductility balance of LPBF 316H stainless steel through post-processing heat treatment.