مشخصات پژوهش

Austenite films with almost identical thicknesses of nanoscale bainitic ferrite plates in a bainitic sheaf and also austenite micro blocks separating bainitic sheaves spreading in different crystallographic directions, are the main factors controlling the toughness and ductility properties in nanostructured bainitic steels. This work aims to investigate how different heat treatment procedures and production methods would affect the impact toughness and tensile ductility in nanostructured bainitic steels. Primarily, bainitic transformation has been applied at different heat treatment temperatures for optimum heat treatment times at which bainite transformation completed and toughness and ductility properties have been assessed according to the volume fraction, morphology and mechanical stability of retained austenite. Consequently, austempering heat treatment has been conducted for times longer than the optimum heat treatment times and toughness and ductility have been evaluated based on the microstructural characteristics and changes. Achieved results have been compared with those of obtained at the end of optimum heat treatment conditions. Additionally, toughness and ductility properties in nanostructured bainite achieved from primarily deformed parent austenite have been investigated based on the microstructural evolutions and different size distributions of microstructural constituents in ausformed samples and results have been compared with those of achieved in simple heat treatment procedure. Finally step-austempering has been applied to investigate the microstructural evolutions and their effect on comprehensive mechanical properties emphasizing on toughness and ductility.