Tensile behaviour of a nanocrystalline bainitic steel containing 3 wt% silicon

Much recent work has been devoted to characterize the microstructure and mechanical properties bainitic nanostructured steels. The microstructure is developed by isothermal heat treatment at temperatures as low as 125–350 °C and adapted steel grades typically contain high carbon contents to achieve sufficient depletion of the BS–MS temperature range, and above 1.5 Si wt.% to suppress carbide formation during isothermal holding. On the latter, most of the published literature agrees on a limit of around 1.2–1.5 wt.% to suppress cementite in high carbon steels. For this reason perhaps, additions of Si significantly above this limit have not been investigated systematically in the context of nanostructured bainitic steels. The present work is concerned with the effect of up to ∼3 Si wt.% in a steel grade adapted to low temperature bainitizing. Tensile properties as compared to similar grades, though with lower Si contents, exhibited unrivalled combinations of strength and ductility, with above 21% total elongation for a UTS above 2 GPa. An attempt is made to explain the mechanical properties of this microstructure in terms of some of its most relevant and unique morphological and microstructural features.

► New nano structured bainitc steel design using 3 wt.% of Si and low Mn and Cr ► Kinetics and mechanical properties comparable with the best in their class, Co/Co + Al alloys. ► Isothermal heat treatments at low temperature, 220–250 °C, produced nano-structured bainite. ► Tensile tests revealed an extraordinary combination of strength and ductility. ► Correlation of mechanical properties-microstructural features is attempted.