Applicability of Master Curve Method to Japanese Reactor Pressure Vessel Steels

The Master Curve method has been proposed and recognized worldwide as an alternative approach to evaluate fracture toughness of reactor pressure vessel (RPV) steels in brittle-to-ductile transition temperature range. This method theoretically provides the confidence levels of fracture toughness in consideration of the statistical distribution, which is an inherent property of fracture toughness. In this study, a series of fracture toughness tests was conducted for typical Japanese RPV steels, SFVQ1A and SQV2A, to identify the effects of test temperature, specimen size, and loading rate, and the applicability of the Master Curve method was experimentally validated. The differences in test temperature and specimen size did not affect master curves. In contrast, increasing loading rate significantly shifted master curves to higher temperatures. The lower bound curve based on the master curve could conservatively envelop all of the experimental fracture toughness data. The present rule, in which the lower limit of fracture toughness is indirectly determined by Charpy impact test results, can be too conservative, while the application of the Master Curve method may significantly reduce the conservativity of the allowable level of fracture toughness.