Nature of the Scatter in the Impact Toughness of Low-Carbon, Low-Alloy Steel for Fracture under Ductile-to-Brittle Transition Conditions

摘要

Using commercial low-alloy steel as an example, we have studied the nature of the increased scatter in impact toughness in the temperature range of the ductile-to-brittle (D-B) transition by multiple impact toughness tests and examined the microstructure of the steel by electron backscatter diffraction (EBSD). The results demonstrate that the scatter in the impact toughness of the low-alloy steel in the case of fracture in the temperature range of the D-B transition is due to toughness nonuniformity in the plastic zone. To assess the local toughness nonuniformity of the plastic zone in the microstructure of particular specimens fractured in the range of the B-D transition, we evaluated the percentage of the total length of ductile/brittle microcracks. We have demonstrated conceptual feasibility of developing a method for separating the contributions of local plastic deformation preceding and accompanying fracture for particular specimens in the range of the D-B transition using EBSD.