Effects of Surface Morphology and Distributed Inclusions on the Low Cycle Fatigue Behavior of Miniaturized Specimens of F82H Steel

Depending on the pulse lengths, the operating conditions, and the thermal conductivity, oscillating temperature gradients will cause elastic and elastic-plastic cyclic deformation giving rise to (creep) fatigue in the structural first wall and blanket components of a nuclear fusion reactor. Small specimen testing technology (SSTT) and related remote control testing techniques are indispensable for the effective use of the limited volumes of materials test reactor and proposed intense neutron sources for the fusion materials test. In order to perform an accurate fatigue lifetime assessment using small specimens, the effects of material factors (surface morphology, inclusion, etc.) on low cycle fatigue (LCF) is mandatory. In this work, the LCF properties of reduced activation ferritic/martensitic steel (F82H IEA heat) were examined for three kinds of surface morphology using miniaturized hourglass-type fatigue specimens (SF-1), and a correlation between LCF crack initiation/propagation and distribution of inclusions was found. Fracture surfaces and crack initiation sites were investigated by scanning electron microscopy (SEM).