Low Cycle Fatigue Behaviour of Ex-Service P92 Steel at Elevated Temperature

Abstract

The influence of strain amplitude and strain rate on low cycle fatigue (LCF) behaviour of the ex-service P92 steel at temperature of 600°C has been examined. Fully reversed strain-controlled LCF tests were conducted at the strain amplitude between ±0.4% and ±0.8% employing strain rate of 2.4x10-3s-1 to 2.4x10-5s-1. The material has been found to exhibit continuous cyclic softening behaviour throughout the LCF tests, and there was no saturation stage observed. The number of cycles to failure decreased with lowering the strain rate and increasing strain amplitude. Mathematically, the relationship between time to failure and strain rate can be expressed by a power law relation. Elastic-plastic finite element (FE) analysis was carried out to obtain the hysteresis loop and cyclic stress response of the material. The computation results are shown to be in good agreement with the experimental data. Fractographic examinations of the fatigued specimens were performed using scanning electron microscopy (SEM). Under the LCF condition at higher strain rates, the crack propagated intergranularly which due to fatigue while at lower strain rates the crack may be propagated in both inter- and transgranular manner.