| Effects of tensile hold time on the high temperature low cycle fatigue life of 12%Cr-Mo-V steel was investigated at 873K in air atmosphere. In order to investigate the effect of creep-fatigue interaction, the hold times at tensile peak strain were imposed to be 10, 30 and 60min. The experimental results show that, with decreasing plastic strain range and increasing tensile hold time, the fatigue lives of 12%Cr-Mo-V steel under creep-fatigue cycling are significantly decreased compared with the faigue ones of this material under continuous cycling. This is considered to be caused by creep cavitation damage which occurred during tensile hold time. It is found that creep cavities are nucleated not only on prior austenite grain boundaries but also within prior austenite grains(lath martensite boundaries). From the results of creep-fatigue cycling, the fracture mode was observed to be mixed(trans and intergranular). The fatigue lives under creep-fatigue cycling are discussed in terms of a model for life prediction previously developed by creep cavitation damage rather than surface crack initiation and propagation. The predicted creep-fatigue lives are in good agreement with experimentally observed ones for 12%Cr-Mo-V steel with increasing tensile hold time. |
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