Study on K_Ic master curve of used turbine rotors

In this paper, master curve of plane strain fracture toughness, K_Ic, for used turbine rotors subjected to temper embrittlement is studied by rearranging a total of 64 data. Fracture appearance transition temperature, FATT, of 2mm V-notch Charpy impact test of the target material was 99 to 181°C, and the thickness, B, of the fracture toughness test specimens used was 200, 100, 50 and 25mm. When the test temperature, T, is arranged by excess temperature, Te, (=T-FATT), K_Ic data have small variation regardless of the FATT value and the intermediate K_Ic value is represented by the same formula as the master curve of ASTM E1921. The relationship between K_c,_1T data, which are fracture toughness for 1CT specimens (B=25mm) converted from each K_Ic data of B=200, 100, 50 and 25mm according to ASTM E1921, and T_e was also obtained. The variation of K_c,_1T data is larger than that of K_Ic data. The nine pieces of K_c,_IT data converted from ten K_Ic data of B=200 and 100mm are located around the upper limit of the variation, and 6 pieces of them exceeded the 95% confidence limit obtained according to ASTM E1921. The reason for the small variation in K_Ic data of the used turbine rotors was also discussed. (author)