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 du ctility and tough ness. In addition, recent work indicated decreased toughn ess during reverse-cyclic loading that has implications on reliability of t hese structures under seismic loading conditions, This paper summarizes the authors recent work on these aspects, along with synergistic effects of in terstitial impurity atoms and radiation-induced point defects, which result in interesting beneficial effects of radiation exposure at appropriate tem perature and strain-rate conditions. While the cyclic loading effects on to ughness are studied in A516 steel, the dynamic strain aging and radiation-d efect interactions were investigated on pure iron as well as several ferrit ic steels. In addition, studies on fast vs. total (thermal+fast) neutron sp ectra revealed unexpected results due to the influence of radiation exposur e on source hardening component of the yield stress; grain size of pure iro n plays a significant role in these effects. The paper concludes with futur e research needed to address these concerns.