A parametric study of irradiation-assisted stress corrosion cracking initiation of additively manufactured 316 L stainless steel by using microstructurally-graded specimen

Different from traditional wrought 316 L stainless steel (SS), the microstructure of 316 L SS made by additive manufacturing (AM) 316 L SS varies significantly depending on the manufacturing and heat treatment conditions. The effects of processing and microstructure on nuclear-related properties are needed as a regulatory basis to accept AM for nuclear use. However, a large parametric study of irradiation-assisted stress corrosion cracking (IASCC) in AM 316 L SS is challenging due to the cost and time involved in evaluating IASCC. This study employed microstructurally graded specimens as a high-throughput method to evaluate IASCC behavior of AM 316 L SS manufactured by directed energy deposition (DED) under a range of laser manufacturing parameters and heat treatment conditions. For the first time, three IASCC modes (intergranular, intragranular, and transgranular) were identified simultaneously on DED AM 316 L SS; however, their contributions to the overall damage varied depending on the material conditions. Heat treatment showed the largest impact on cracking susceptibility with laser processing parameters exhibiting a secondary effect. The cracking susceptibility of DED AM 316 L SS was highest in the 930 °C heat treatment, while the 650 °C and 1121 °C heat treatments showed lower magnitude. The contributions of various mechanistic factors to these IASCC modes, including dislocation cells, radiation hardening, manufacturing-related precipitates, and strain incompatibility caused by the broad grain size distribution, were discussed in detail.