Prediction of fracture toughness of SA738Gr.B steel in the ductile-brittle transition using master curve method and bimodal master curve method

Abstract

The low temperature fracture toughness of SA738Gr.B steel is as important as its strength, but the low temperature fracture toughness tends to be more complicated due to some deterministic and random inhomogeneity, such as sampling locations. In this paper, the fracture toughness of the 60 mm thick SA738Gr.B sheet in DBT region from the surface to the center was characterized by MC method and BMC method. Considering the sampling position, a distinct trend is found that the toughness of the surface is significantly higher than that of the center and T0 is lower from center to the surface due to the faster quenching rate. Special attention was paid on the discussion of the applicability of China-produced SA738Gr.B steel to the master curve (MC) method. It was found that the inhomogeneity caused the actual distribution of the experimental data to deviate from the three-parameter weibull distribution, and the weibull slope was lower than the theoretical value of 4. Characterizing the fracture toughness of materials containing heterogeneous components by the MC method can overestimate the fracture toughness and may pose a potential hazard. The BMC method can effectively solve the problem of material inhomogeneity. It is an evaluation method based on the actual toughness distribution of materials. The BMC method takes into account the influence of material inhomogeneity on the toughness estimation, and more accurate assessment of material scatter than the standard MC method yields a slightly conservative but more appropriate prediction.