Prediction of Graphitization Behavior during Long-Term Creep in Carbon Steels

Carbon steels with ferrite and pearlite microstructures suffer from graphitization by the decomposition of cementite when exposed to elevated temperatures for long periods. Graphitization degrades the mechanical properties of the steels and increases its risk of failure. Therefore, by considering the extended life span of a thermal power plant, where carbon steels are used at elevated temperatures, evaluation of graphitization risk is necessary. This study evaluates the effect of temperature, stress, time, and chemical composition for both elongated and spherical graphitization using logistic regression of previously reported graphitization conditions in long-term creep ruptured specimens and establishes a prediction formula for graphitization occurrence. In addition, the accuracy of the prediction formula was validated by investigating the graphitization behavior of other carbon steels.