Evaluation of Ductile-Brittle Transition of Fracture Toughness by Material Degradation

When huge energy transfer systems like nuclear power plants and steam power plants are operated for long times at high temperatures, mechanical properties change and ductile-brittle transition temperature increases by degradation. So we must estimate the degradation in order to assess safety, life expectancy, and other operation parameters. The sub-sized specimen test method using the surveillance specimen, and BI (Ball Indentation) method were developed for evaluating the integrity of metallic components. In this study, we will present the evaluation of the ductile-brittle transition temperature using the BI test and the sub-sized specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test, the fracture toughness test, and the BI test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with those of the BI test. The evaluation technique of the ductile-brittle transition temperature using the BI test was also discussed. Our results show that the ductile-brittle transition temperatures rose as the aging time increased. We suggested that the fracture toughness results of the sub-sized specimen test and the IEF results of the BI test could be used in the estimation of the ductile-brittle transition temperature as material degrades.