Investigation on low cycle fatigue properties of CLAM steel electron beam welded joint at 550 °C

Abstract

The low cycle fatigue (LCF) properties of structural materials at high temperatures are important for operational safety of fusion reactors. In this work, the investigation on LCF properties of CLAM steel joints welded by electron beam was conducted at strain amplitudes varying from 0.2 % to 0.7 % at 550 °C. It is found that the fatigue life and cyclic stress response of welded joints are lower than those of base metal. Continuous cyclic softening is observed in welded joints and base metal during LCF test. A majority of the fatigue cracks initiated at the surface of the the welded joint specimen with several initiation sites and propagated in a transgranular mode. The area of the crack propagation region decreased and the fatigue striation spacing increased with increasing strain amplitude. The cyclic softening is attributed to the coarsening of martensite laths and the reduction in dislocation density.