Effect of ausforming temperature on bainite morphology in a 3.2% Si carbide-free bainitic steel

The effect of ausforming temperatures on bainite morphology was investigated on a newly developed carbide-free high-silicon steel. High plastic deformation (30%) was applied to undercooled austenite after austenitization in the temperature range 900–300 °C with a Gleeble 3800 thermomechanical simulator working in compression mode, before the isothermal treatment at 300 °C for bainitic transformation. Samples were fully characterized by means SEM, XRD, EBSD and TEM. Results showed that reducing the deformation temperature, prior to the bainitic transformation, ausforming increased undercooled austenite strength, leading to the decrease of maximum volume fraction of bainitic ferrite, due to mechanical stabilization. Moreover, it was observed a strong impact on bainite morphology of the deformation temperature including length of sheaves, the reciprocal orientation of the bainitic plates and crystallographic orientation, with the detection of variant selection phenomena.