Study on fracture toughness evaluation method of SA738Gr.B steel heat affected zone in ductile-brittle transition region

The Master Curve (MC) method is widely used to evaluate the fracture toughness of ferritic steels for reactor pressure vessels in the ductile-brittle transition zone, but this method is only applicable to macroscopically uniform ferritic steels. Based on the measured fracture toughness data of China-produced SA738Gr.B steel Heat-Affected Zone (HAZ) in the as-welded and heat-treated state, the problems of the standard MC method for characterizing the fracture toughness of the HAZ are discussed. Then the Bi-modal master curve method (BMC), SINTAP method, and Single point estimation method (SPE) were used to characterize the fracture toughness of the HAZ of SA738Gr.B steel in the ductile-to-brittle transition zone. The comparative analysis found that the BMC method is better in terms of the accuracy of the estimation and the over-dispersion envelope was caused by the heterogeneity. The estimation results of the SINTAP and SPE models are conservative but can be used for the safety evaluation of the actual structure. The study provided technical support for SA738Gr.B steel to exempt post-weld heat treatment issue.