Effect of ausforming temperature and strain on the bainitic transformation

In this work, the effect of ausforming temperatures and strain level on bainitic transformation and morphology were investigated on a newly developed carbide-free high-silicon steel. High plastic deformations (0.2 ÷ 0.5%) were applied to undercooled austenite after austenitization in the temperature range 900-330 °C with a Gleeble 3800 thermomechanical simulator working in compression mode, before quenching or the isothermal treatment at 300 °C for bainitic transformation. Specimen characterization and the application of a thermodynamic approach showed that depending on the deformation temperature, before the bainitic transformation, strain-induced transformations that accelerate the transformation may occur. Moreover, it was observed a strong impact of the deformation temperature on bainite morphology including length of sheaves, size of the blocks, the reciprocal orientation of the bainitic plates and crystallographic orientations, with the detection of variant selection phenomena.