Research on laser powder bed fusion process microstructure and mechanical properties of nuclear-grade 316LN stainless steel

Abstract

Laser powder bed fusion (L-PBF) technology has undergone rapid development in recent years. Owing to its advantages of high speed, efficiency, intelligence, and full flexibility, it exhibits significant potential for realizing the lightweight and efficient manufacturing of nuclear equipment, thereby substantially promoting the transformation and upgrading of the nuclear industry. This study employs nuclear-grade 316LN stainless steel as the research subject. Microstructural and mechanical property specimens were fabricated using the L-PBF process under different processing parameters. The relative density, microstructure, of the 316LN specimens were characterized using equipment such as optical microscopy and scanning electron microscopy, leading to the identification of the optimal L-PBF processing window for 316LN material. Furthermore, heat treatment processes for L-PBFed 316LN were investigated, elucidating the trend of property variations at different temperatures and identifying the optimal heat treatment regimen. The results indicate that the 316LN material achieves relatively high internal density and exhibits superior overall microstructural morphology when the volumetric energy density exceeds 50 J mm−3. The optimal solution treatment process was determined to be 1040 °C, held for 2 h, followed by argon cooling. Additionally, hot isostatic pressing treatment can compensate for the reduction in plasticity induced by rapid cooling and enhance the ultimate tensile strength at the expense of yield strength. In engineering applications, appropriate post-processing methods can be selected based on specific service conditions.