Analysis of long-term creep curves by constitutive equations

Long-term creep curves up to the secondary stage (time >105 h) for carbon steel, 1.25Cr-0.5Mo-Si steel, 2.25Cr-1Mo steel, and SUS316 steel were analyzed by means of constitutive creep equations. A power-law equation well fitted the actual long-term creep curves for all the steels, whereas the exponential-law equation, logarithmic-law equation, and Blackburn's equation could not represent the beginning of primary creep during long-term testing. All the equations reproduced short-term creep curves for all the steels. For carbon steel, the parameters obtained from data analysis at higher stresses were extrapolated to lower stresses to predict the long-term creep curve. However, none of the creep curves predicted by the equations agreed with the actual long-term creep curves, although the prediction of the power-law equation was better than those of the other equations.