Complexity of segregation behavior at localized deformation sites formed while in service in a 316 stainless steel baffle-former bolt

Post-irradiation evaluation was performed on a 316 stainless steel baffle former bolt harvested after 40 years of service in a pressurized water reactor. Microstructure analysis revealed the presence of defect-free dislocation channels and strain-induced twins, indicative of loading at a stress level close to yield stress at least once while in service. Primary radiation-induced Ni/Si precipitates were likely destroyed during channel and twin formation, and secondary, significantly coarser Ni/Si precipitates formed inside the newly formed dislocation channels and along ∑3 boundaries during the continued irradiation. Complex chemistry inside the strain-induced features may overlap with dislocation pileups and impact localized corrosion and material long-term performance.