Effects of ausforming on isothermal bainite transformation behaviour and microstructural refinement in medium-carbon Si–Al-rich alloy steel

• Effects of ausforming on isothermal transformation and microstructure is studied.
• Nanostructured bainite is produced by isothermal transformation after ausforming.
• Lowering temperature and increasing strain reduce transformation incubation.
• Lowering temperature and increasing strain refine bainite and enhance hardness.
• Strain rate has a weak influence.

The effects of ausforming temperature, strain and strain rate on isothermal bainite transformation behaviour and microstructural refinement in medium-carbon Si–Al-rich alloy steel were determined by thermomechanical simulation. Results show that ausforming decreased the martensite start temperature and enabled isothermal transformation at low temperatures, resulting in the formation of nanostructured bainite. Decreasing the ausforming temperature and increasing the ausforming strain did not only reduce the incubation of isothermal transformation but also refined bainite lath and enhanced the hardness of the alloy steel. Strain rate showed a weak influence on the transformation behaviour and microstructure of the obtained nanostructured bainite.