Effect of solution treatment on the intergranular corrosion behavior of 316L stainless steel fabricated by selective laser melting

Selective laser melting (SLM) is a powder-bed metal additive manufacturing technology that is extensively employed in the fields of marine engineering, biomedicine, and nuclear power due to its high processing precision and wide range of applicable materials. 316L stainless steel is one of the metal materials that have been researched earlier and has a more mature process in the field of SLM. Although SLM technology processing of 316L stainless steel parts (later referred to as SLM-316L stainless steel) has been conducted for industrial applications, it is rarely utilized for high temperatures, strong corrosion, complex loads, and other demanding conditions. Nonequilibrium solidification in the laser melt pool is an inherent mechanism of the SLM-316L stainless steel forming process, which contributes to the production of a nonuniform organizational structure and a high level of residual stress, which influence the reliability of SLM-316L stainless steel in long-term service. Heat treatment after preparation of SLM-316L stainless steel is the most effective approach to optimizing the organizational structure and reducing residual stress. SLM of 316L stainless steel is often employed for solid solution treatment to optimize the organization and reduce residual stresses to yield remarkable overall performance. The intergranular corrosion behavior of austenitic stainless steel highly depends on its organizational structure; thus, solid solution treatment is bound to enhance the intergranular corrosion performance of SLM-316L stainless steel. However, the law and mechanism of the effect of solid solution treatment on the intergranular corrosion behavior of SLM-316L stainless steel is still vague. Based on the mentioned above, in this work, solid solution treatment of SLM-316L stainless steel is conducted at 1150 ℃, its organizational and structural characteristics and morphology of nanooxidized particles are examined by Scanning electron microscope (SEM), Electron backscattered diffraction (EBSD), and Transmission electron microscope (TEM), and its intergranular corrosion behavior is investigated by double-loop electrochemical reactivation and ammonium persulfate electrolysis tests. The following conclusions can be drawn. (1) Recrystallization of SLM-316L stainless steel takes place after solid solution treatment, forming regularly shaped equiaxed grains and annealed twin crystals. (2) The nanooxidized particles are coarsened, and the maximum size at grain boundaries can attain the micrometer level. Meanwhile, the type of oxide particle also transforms from the rhodochrosite structure of MnSiO₃ to the spinel structure of CrMn₂O₄. (3) Solid solution treatment results in a decrease in intergranular corrosion performance of SLM-316L stainless steel, together with a decrease in intergranular corrosion performance, which, in turn, is accompanied by sensitization time extension, and the type of intergranular corrosion changes from step-like to groove-like.