Ductile-to-Brittle Transition in Low-Alloy Steel: A Combined Experimental and Numerical Investigation

Ductile-to-brittle transition in a low-alloy bainitic steel used as reactor pressure vessel material coincided with the change in brittle facet plane normal(s). Experimentally, it changed from similar to {100} facets at low temperatures to off-{100} planes at the higher temperatures. And such a change was also associated with brittle-to-ductile transition in the fracture mode. Molecular dynamics simulations, however, showed that the intrinsic cleavage plane remained {100} at all temperatures. Activation of atomistic mechanisms of crack kinking and dislocation pile-up, at higher temperatures, followed by the creation of atomistic ledges at the free surface resulted in the appearance of off-{100} facets