On the ductile to brittle transition in austenitic steel

The fracture mode of austenitic steel may feature a ductile to brittle transition (DBT), depending on alloy composition and temperature. As crack nucleators, intersecting deformation twins play a key role in determining the fracture mode. In particular, brittle fracture occurs at low temperature deformation of high nitrogen steel where twins are very thin and the dislocation density is extremely low. The DBT is discussed in terms of microstructure and stress state. It is shown that for thin twins and low dislocation density: (i) twin-twin penetration is suppressed; and (ii) the tip of a growing crack cannot blunt.