Effect of 10% ausforming on impact toughness of nano bainite austempered at 300 °C

The volume fraction and morphology of the microstructural constituents are extremely important when discussing the impact toughness of nanostructured bainitic steels. On the other hand, microstructural features can be influenced by plastic deformation of austenite prior to isothermal bainitic transformation. This paper aims to investigate the effect of 10% ausforming process before austempering heat treatment on impact toughness of nanostructured low temperature bainitic steels austempered at 300 °C. Results indicate that the volume fraction and morphology of high carbon retained austenite within the microstructure are important factors affecting the impact toughness energy. However results showed that the role of bainitic sheaves cannot be ignored due to their valuable effect of arresting/deflecting the cracks. It has been found that bainitic sheaves grow at more limited crystallographic variants in ausformed samples which can influence the value of the impact energy absorbed during straining the samples.