Effect of hold time on low cycle fatigue behavior of 13CrMo44 steel at 833K was investigated in air, argon and hydrogen atmosphere. Each of total strain amplitude was controlled to be 1.0, 1.4 and 2.0% with zero mean strain. To see the effect of creep, hold time at tensile peak strain was controlled to be 1, 5, 10 and 30 min. and the results obtained were compared with the continuous cycling data.
The experimental results show that applied hold time at tensile peak strain decreases the fatigue life in the conducted test condition and the creep cavitation damage is formed during creep-fatigue cycling. In this investigation a model for the life prediction for low cycle fatigue with hold time at tensile peak strain is suggested for the life prediction for the temperature range of 0.5$T_m$. This model is formulated on the basis of the assumptions that the creep cavities are formed due to the vacancies generated during fatigue, and are grown during hold time. The fatigue crack nucleated at the surface due to fatigue loading is affected by creep damages for it's propagation. The model is checked by experimental results with various hold time period and the predicted creep-fatigue lives are in good agreement with experimentally observed ones.
Fatigue life in air environment at high temperature is very much reduced. This is believed to be related to the oxidation at the crack tip.
Hydrogen reduces the fatigue life at continuous cycling and cycling with short hold time. This is believed to be related to cavity nucleation enhancement by hydrogen.
From the experimental results, we believe that cavities are nucleated by vacancy clustering and are grown by vacancy diffusion through the grain boundaries. The cavities are formed in every cycle and the number of nucleated cavities per cycle is proportional to the plastic strain range.
