EVALUATION OF CREEP DEFORMATION AND RUPTURE LIFE OF 1.3MN-0.5MO-0.5NI STEEL BY MODIFIED THETA-PROJECTION CONCEPT

Creep curves of 1.3Mn-0.5Mo-0.5Ni steel were analyzed using the modified theta-projection concept based on the following equation: epsilon = epsilon(0) + A{1 - exp( - alpha-t) } + B{ exp(alpha-t) - 1} where epsilon is the strain, t is the time, and epsilon(0), A, B and alpha are the parameters determined by curve fitting. The equation could describe the measured creep curves over the whole creep stages up to 90 percent of the rupture life. The modified theta-projection concept could successfully predict long term ruptures lives obtained independently on the same material. Heat-to-heat variations in creep properties were discussed on the basis of the creep curve analysis. The parameters epsilon(0), A and alpha, were invariable among all the heats investigated. Only the parameter B related to the weakening process was different among the heats, indicating that the difference in the weakening parameter B was primarily responsible for the heat-to-heat variations.