Post-treatment-dependent improvement in stress corrosion cracking resistance of L-PBF 316L stainless steel after long-term thermal aging in simulated PWR primary water

The effect of long-term thermal aging (400 °C for 10,000 h) on the stress corrosion cracking (SCC) behavior of laser powder-bed fusion 316L stainless steel was investigated in simulated pressurized water reactor (PWR) primary water for two engineering-relevant post-processing conditions: stress relief (SR) and hot isostatic pressing (HIP). Although long-term aging significantly reduced the SCC crack growth rate in both conditions, the mechanisms responsible for this improvement differed fundamentally. In the HIP condition, aging mitigated grain-boundary Cr depletion, promoting local passivation and suppressing preferential intergranular cracking. In the SR condition, aging reduced Cr segregation and geometrically necessary dislocation accumulation at cellular boundaries, thereby relaxing the coupled chemical and mechanical heterogeneities associated with the cellular network and changing the dominant crack propagation mode from transgranular to intergranular cracking. These results demonstrate that the SCC response of L-PBF 316L during service-relevant thermal exposure is governed by post-processing-dependent microstructural evolution rather than a universal aging effect.