Stress dependence on stress relaxation creep rate during tensile holding under creep-fatigue interaction in 1Cr-Mo-V steel

A quantitative analysis of the stress dependence on stress relaxation creep rate during hold time under creep-fatigue interaction conditions has been conducted for 1Cr-Mo-V steel. It was shown that the transient behavior of the Norton power law relation is observed in the early stage of stress relaxation in which the instantaneous stress is relaxed drastically, which occurs due to the initial loading condition. But after the initial transient response in a 5 hour tensile hold time, the relations between strain rate and instantaneous stress represented the same creep behavior, which is independent of the initial strain level. The value of stress exponent after transition was 17 which is the same as that of the typical monotonic creep suggested from several studies for 1Cr-Mo-V steel. Considering the value of the activation energy for the saturated relaxation stage, it is suggested that the creep rate is related to instantaneous stress and temperature by the Arrhenius type power law. (C) 1999 Kluwer Academic Publishers.