Fracture in ferritic reactor steel—dynamic strain aging and cyclic loading

Ferritic steels commonly used for pressure vessels and reactor supports in light water reactors exhibit dynamic strain aging resulting in decreased ductility and toughness. In addition, recent work indicated decreased toughness during reverse-cyclicloading that has implications on reliability of these structures under seismic loading conditions. This paper summarizes the authors’ recent work on these aspects, along with synergistic effects of interstitial impurity atoms and radiation-induced point defects, which result in interesting beneficial effects of radiation exposure at appropriate temperature and strain-rate conditions. While the cyclic loading effects on toughness are studied in A516 steel, the dynamic strain aging and radiation-defect interactions were investigated on pure iron as well as several ferritic steels. In addition, studies on fast vs. total (thermal+fast) neutron spectra revealed unexpected results due to the influence of radiation exposure on source hardening component of the yield stress; grain size of pure iron plays a significant role in these effects. The paper concludes with future research needed to address these concerns.