Effect of heat treatment on corrosion and fatigue behavior of SLM-produced SS316L structure

• Investigates corrosion-fatigue response of SLM 316L, a sparsely explored domain. • As-built SLM samples showed 60.6% lower corrosion rate than heat-treated ones. • Heat-treated samples lost ∼75% of UTS and hardness after corrosion exposure. • HT samples, though stronger, had lower fatigue life due to SCC and sensitization. This study examines the effect of heat treatment on the mechanical and corrosion properties of 316L stainless steel fabricated using Selective Laser Melting (SLM). A comparative analysis was conducted between as-built and heat-treated specimens, with the latter subjected to annealing at 1150 °C followed by controlled furnace cooling. Comprehensive characterization included microstructural analysis, compositional assessment, tensile, fatigue, and hardness testing. Heat-treated samples exhibited significant improvements in mechanical properties, with tensile strength increasing by 28% (from 465 MPa to 598 MPa) and microhardness by 22% (from 197 HV to 240 HV), primarily due to the precipitation of chromium carbides. However, fatigue life slightly declined post-heat treatment, along with a shift in failure mode from intergranular to transgranular cracking. Corrosion testing in a 3.5 wt% NaCl solution revealed that as-built samples exhibited superior corrosion resistance, with a 60% lower corrosion rate than heat-treated samples. This reduction in corrosion resistance is attributed to chromium depletion near grain boundaries and the presence of MnS inclusions, which acted as pitting initiation sites in heat-treated samples. Post-corrosion mechanical testing showed a significant degradation in the heat-treated samples, with ultimate tensile strength and microhardness decreasing to nearly one-fourth of their original values. Fatigue performance also deteriorated due to sensitization-induced susceptibility to stress corrosion cracking. Overall, the study highlights that while heat treatment enhances bulk mechanical properties, it compromises corrosion resistance and fatigue performance in aggressive environments. These findings are crucial for optimizing post-processing treatments of SLM-produced stainless steel components intended for service in corrosive or fatigue-critical applications.