Comparative Evaluation of the Low Cycle Fatigue Behaviours of P91 and P92 Steels

In the present paper, low cycle fatigue (LCF) behaviour of modified 9Cr-1Mo steel (P91 steel) and tungsten allo ed 9Cr steel (P92 steel) is presented. Total axial strain controlled fatigue tests were performed in air employing a constant strain rate 3×10-3s-1 with strain amplitudes in the range ±0.25% to ±0.6% in the temperature range 823 – 873 K. Both steels exhibited a continuous softening behaviour before the final load drop that occurred due to crack propagation. In general, P92 steel exhibited a lower stress response compared to P91 steel. At lower strain amplitudes, P92 steel showed a higher stress response than P91 steel. The softening rate of P92 steel is found to increase with increase in strain amplitude whereas the softening rate of P91 steel has remained constant with strain amplitude. Comparison of fatigue lives of the steels exhibited a mixed behaviour. Fatigue life of P92 was found to be higher at higher strain amplitude and lower at lower strain amplitudes than P91 steel.