Corrosion behavior in lead-bismuth eutectic of 316 L stainless steels fabricated by laser-based powder bed fusion and powder metallurgy-hot isostatic pressing

Abstract

The corrosion behavior of laser-based powder bed fused (LPBF) 316 L under various heat-treatment conditions (as-printed, solution annealed and hot isostatic pressed) in lead-bismuth eutectic (LBE) at 550 °C is studied. The wrought 316 L and counterpart fabricated by powder metallurgy-hot isostatic pressing (PM-HIP) were investigated as references. LPBF 316 L achieves reduced susceptibility to the LBE environment and acquires a shallower corrosion/dissolution depth in comparison to wrought and PM-HIP 316 L. As-printed and hot isostatic pressed LPBF specimens show restricted discernible phase transformation while the other conditions exhibit significant phase transformation. The enhanced corrosion resistance of LPBF 316 L in LBE is attributed to a dislocation cellular microstructure, a high proportion of low-angle grain boundaries, and elevated chromium and silicon contents. Dislocation cell boundaries and twin boundaries have higher resistance to LBE ingress than the high-angle grain boundaries. Compared to the matrix, the preferential corrosion by LBE of LPBF materials at columnar boundaries is related to the carbides and (Si, Mn) enriched oxides formed during LPBF process. LPBF-HIP material exhibits a three-dimensional alternating structure of recrystallized and unrecrystallized areas, effectively impeding LBE ingress and thus can be a promising candidate as the structural material in the LBE system.