Fracture surface morphologies in ESSO test specimens were examined to investigate the enhancement of brittle crack arrest toughness due to texture. In the steels with high crack arrest toughness due to texture, many sub-cracks were detected on the fracture surface during fast crack propagation. The cross sectional observations of the fracture surfaces revealed that these sub-cracks on fracture surface resulted from crack-micro-branching. The mechanism of crack-micro-branching was also investigated from the viewpoint of the crystallographic orientation. FEM analyses were also conducted to examine the effect of crack-micro-branching on the stress intensity factor. The dominant effect of crack-micro-branching to reduce the fracture driving force during brittle crack propagation was discussed, comparing with the effect of macroscopic zigzag crack propagation.
