Effect of Thermal Aging on Material Strength and Fracture Behavior in Mod.9Cr-1Mo Steel

The material properties of heat resistant materials are known to be affected by thermal aging as operating time is accumulated at power plants. In this study, the influence of thermal aging on yield strength, ductility and J-Resistance behavior for Mod.9Cr-1Mo (ASME Grade 91) steel which is a material widely adopted for Generation IV nuclear energy system has been investigated. Service exposed Gr.91 steel materials sampled from a piping system of an ultrasupercritical (USC) plant in Korea with accumulated operation time of 73,716 hours were used for material testing. The test results of the service exposed material were compared with those of the virgin Gr.91 steel. Those test data were compared with the material properties of ASME code and RCC-MRx code that are international elevated temperature design codes. Conservatism of the material properties in design code has been quantified based on the comparison of virgin and service exposed materials.