Creep modeling and creep life estimation of Gr.91

The creep behavior and deciding factors for creep life have been investigated for Gr.91 in the temperature range between 450 and 725 degrees C. The longest time to rupture was 68 755 h. The creep life is inversely proportional to the minimum creep rate multiplied by the increase in creep rate by strain in the acceleration region for a wide range of test temperature and duration. The minimum creep rate depends on both the time to minimum creep rate and the strain to minimum creep rate. The strain to minimum creep rate decreases with decreasing stress, suggesting that the creep deformation in the transient region is significantly inhomogeneous at low stresses. The creep life is correlated with the creep deformation parameters in the transient region so that we can predict the creep life from a short-term creep test for up to the end of transient region, corresponding to less than 30% of the creep life, without any stress extrapolation.