Toughness variations in nanostructured bainitic steels

Outstanding combination of strength and ductility in nanostructured bainitic steels makes them prone to be used as an important engineering material. However, there is still a necessity to investigate their toughness and effective parameters. This work aims to study the fracture toughness of these group of high strength carbide free bainitic steels with respect to chemical composition, transformation temperature, volume fraction and morphology of the present phases in the microstructure. Results indicate that the volume fraction and morphology of high carbon retained austenite together, are important factors affecting the ductility. In addition, higher amount of the lathlike austenite is essential in order to improve fracture toughness. Moreover, it has been shown that controlling the mechanical stability of retained austenite and the primary austenite grain size by Ni and V addition can further influence fracture toughness of nanostructured bainitic steels.