| The effects of deformation-induced martensite on three-point bending fatigue properties of austenitic 304 stainless steel sheets at room temperature and -162℃ were investigated. The fatigue properties at -162℃ were superior to those at room temperature due to the higher volume fractions of deformation-induced martensite. In room temperature testing, the mean load amplitude increased steadily with cycles, which means that cumulative plastic incubation strain is required for martensite transformation. On the contrary, in specimen tested at -162℃, the mean load amplitude increased rapidly within a few cycles due to the rapid transformation of austenite to martensite and slightly decreased after the maximum due to dynamic recovery. Two kinds of deformation-induced martensite, namely ε-martensite (hcp structure) and α`-martensite (bcc or bct structure), were found depending on the testing temperature and total strain. The ε-martensite nucleated from overlapped stacking faults and grew into $lt;112$gt;_γ direction. The α`-martensite nucleation was associated with the formation of dislocation pile-ups on active slip planes of austenite and α`-martensite was found to be the dominant phase in high strain or low temperature. |
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