The Heat Treatment Effects on the Microstructure, Hardness, and Sigma Phase Content of L-PBF SAE 316L Stainless Steel

This research aims to enhance the understanding of the interrelationships among the manufacturing process, microstructure, and mechanical properties in the Laser Powder Bed Fusion (L-PBF) of SAE 316L stainless steel (SS), which can lead to the appearance of undesirable phases, like sigma (σ).As part of this investigation, as-built samples underwent solubilization heat treatment (HT), primarily targeting the dissolution of the σ phase and microstructure homogenization, with a subsequent assessment of its impact on hardness.The study reveals the efficacy of HT in reducing σ phase content, particularly following treatments at 950°C and 1,050°C for 2 h.Notably, the dissolution of the process-induced microstructure becomes progressively significant within the temperature range of 800-950°C for 2 h.Furthermore, the study identifies a hardening effect associated with the process-induced microstructure on the samples.Remarkably, the sample exhibiting the highest hardness value featured a substantial σ phase content and maintained the process-induced structure after HT.