Low cycle fatigue and ratcheting behavior of 35CrMo structural steel at elevated temperature

•Ratcheting/shakedown behavior was estimated by the steady ratcheting rate.•Different fracture failure mechanisms were found for various stress rates.•The viscous stress component increases significantly with decreasing the stress rate.•The maximum fracture strains for various stress rates remain approximately constant. Low cycle fatigue and ratcheting deformation of 35CrMo steel under uniaxial stress-controlled loading were investigated at 500°C. The effects of stress rates for 0.125MPa/s, 0.5MPa/s, 2.5MPa/s, 10MPa/s, 25MPa/s and 40MPa/s, and peak stresses σmax for 200MPa, 300MPa, 400MPa and 500MPa, were discussed in detail. Results indicated that the ratcheting strain curve versus cyclic number is similar to traditional static creep curve with three stages and the ratcheting stress rate is lower than the static creep rate with the same peak stress. Shakedown behavior occurs when σ̇ is greater than or equal to 2.5MPa/s for σmax=200MPa, but ratcheting happens for the other loads tested according to the method proposed by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF). Moreover, the viscous stress component σv increases significantly with the decrease of stress rate, which represents the ratcheting deformation of 35CrMo steel is obviously time-dependent under high temperature. Furthermore, stress rate has little effect on fatigue life when the stress rate is less than 2.5MPa/s, while the fatigue life increases exponentially with the increase of stress rate when the stress rate is greater than 2.5MPa/s at σmax=500MPa. It is of interest that the maximum fracture strains for various stress rates remain approximately constant, and the tested average value is 11.6%.