Utility and procedure of fracture toughness evaluation of steels through master curve approach using charpy impact specimens

More often than not, fracture toughness data particularly in the transition region of pressure vessel ferritic steels are subjected to scatter. For designing structures operating in the transition region, an estimate of the lower bound fracture toughness scatter rather than lower bound fracture toughness would be desirable. Irradiation embrittlement being a key issue for the integrity assessment of operating nuclear pressure vessels, the assessment methodology needs to address this issue, This paper presents the origin and imposed limitations of fracture toughness data in transition region of pressure vessel ferritic steels vis-A-vis ASME Code reference toughness curve and the potentials of overcoming the limitation by using Master Curve Approach. The results reported in this paper formed a part of the round robin exercise entitled "Assuring Structural Integity of Reactor Pressure Vessels" initiated by International Atomic Energy Agency in 1996. The Master Curve Approach can be used for the evaluation of fracture toughness of all steels which exhibit a transition between brittle to ductile mode of fracture with increasing temperature, and to monitor the extent of embrittlement caused by metallurgical damage mechanisms.