Formulation of creep curves and rupture lives for long-term creep property prediction with special reference to a 12 Cr (H46) steel.

Abstract

A creep curve equation taking account of all the three creep stages, e=eo+A(1-e-αt)+B(eαt-1)and a rupture parameter P defined byP=(1/α) ln {(er-eo-A)/B}were applied to a 12 Cr (H46) steel to formulate its creep properties. In these equations, e, t and er are creep strain, time and strain to rupture, respectively, and eo, A, B and α are material constants to be experimentally determined.The creep curve equation well described creep curves measured with the H46 steel. Temperature and stress dependence of the four material constants was very convenient to extrapolate them to lower temperatures and stresses, and it was shown that long-term creep curves under usual service conditions of engineering plants (0.9Gs, 2.5×105h) were easily predicted with high accuracy.Ordinary rupture parameters, such as Larson-Miller parameter, are nonlinearly related to stress, and the curvature prevents us from predicting accurate long-term creep lives. In contrast with these parameters, the present one was linearly related to observed values of rupture life, ensuring more accurate extrapolation than the ordinary methods.