Small Punch Creep Life Prediction from Steady-State Deflection Rate in High-Chromium Ferritic Heat-Resistant Steels

Abstract

The small punch (SP) creep deformation and rupture behavior of different high-chromium ferritic heat-resistant steels were studied at various temperatures in the range from 923 K to 1073 K (650 °C to 800 °C) and loads in the range from 65 to 400 N. The creep deflection rate, after an initial abrupt decrease, showed no significant variation during most of the creep time and exhibited a steady-state creep stage. The time to steady-state creep stage accounted for less than 30 pct of the creep rupture life. A close relationship was found to exist between steady-state deflection rate and time to rupture, resembling Monkman–Grant relation. This relationship was independent of the type of steels studied, resulting in a single master curve. This relationship was used for predicting SP creep rupture life. The predicted rupture life was within an accuracy factor of 1.2. The study revealed that the creep rupture life can be reasonably well predicted by evaluating steady-state deflection rate, without waiting for the fracture of specimen to occur. This approach of prediction using steady-state deflection rate was found to be more advantageous than that using minimum deflection rate as the latter appeared relatively close to the onset of acceleration creep.