Effect of Close-Packed Plane Boundaries in a Bain Zone on the Crack Path in Simulated Coarse-Grained HAZ of Bainitic Steel

Global effect of Bain-zone boundaries and the local effect of close-packed plane (CP) boundaries on the path of secondary cleavage cracks (observed on a fractured V-notch Charpy specimen) were visualized and discussed in simulated coarse-grained HAZ of bainitic steel. Microstructural unit map (Bain-zone map and CP map) was obtained by electron backscatter diffraction method for a prior austenite grain of a few hundred micrometers. Furthermore, a correlation between CP boundaries and sites that favored formation of the blocky martensite–austenite (M–A) constituent was confirmed. It was clarified that two crack deviation/local changing factors (CP boundaries and blocky M–A) are paired.