Volume 15, Issue 5 (September 1987)
Evaluation of Intergranular Fracture Initiation in Transition Region of Retired Steam Turbine Rotor Steel Using Small Specimens and the Acoustic Emission Technique
Fracture toughness tests were performed at 150°C in the transition region for a Cr-Mo-V steel using four different sizes of compact tension specimens and with the use of the acoustic emission (AE) technique. Two fracture toughness parameters were obtained to evaluate the intergranular mode fracture toughness: one is the critical fracture toughness of KJC calculated from Jc, the other is a fracture toughness of KJAE characterized by the onset of microscopic pop-in cracking determined by AE. The values of KJC and KJAE of the smaller specimens show a great deal of scatter. Combining the fractographic studies, the source of toughness scatter is discussed in terms of the loss of plastic constraint. The results show that the lower bound values of KJAE in the smaller specimen sizes are coincident with a valid fracture toughness, KIC(AE), of the large specimen. An accurate evaluation of the intergranular mode fracture toughness is also discussed.