純鉄の低温低サイクル疲労における内部き裂発生形態と疲労寿命の関係

抄録

Low-cycle fatigue tests were performed at -140°C using commercial-grade pure iron having an average ferrite grain size of 400 μm. The effect of fracture mechanism on fatigue life properties was investigated, especially on the dispersion of fatigue lives in the high plastic strain range (Δεp) where fracture occurs in an internal fracture mode. Fracture surfaces were observed using a scanning electron microscope. The dispersion of fatigue lives is due mainly to the difference of internal fracting mode. Specimens fractured by intersection of a deformation twin and a grain boundary (T-B type) show longer fatigue lives than those fractured by intersection of deformation twins (T-T type) or a deformation twin and an inclusion (T-I type). The effect of grain size at the internal fracture origination site was also discussed.