Effect of Strain Rate on the Bainitic Transformation in Fe-C-Mn-Si Medium-Carbon Bainitic Steels

The effect of strain rate on the kinetics of the bainitic transformation in a Fe-C-Mn-Si medium-carbon bainitic steel was investigated by dilatometry, metallography, and X-ray diffraction. The results indicate that the bainitic transformation is affected by the strain rate. The bainitic transformation is significantly promoted by deformation at a low strain rate of 0.01 s−1, and the amount of bainite increases further when the strain rate increases to 0.1 s−1. However, as the strain rate increases further to 1.0 and 5.0 s−1, the extent to which deformation promotes the bainitic transformation decreases, and the amount of bainitic transformation is smaller than that at low strain rates. The amount of bainite tends to be constant with increasing strain rate from 1.0 to 5.0 s−1. In addition, the volume fraction of retained austenite shows the same trend as the amount of bainite, indicating that chemical stabilization plays a key role in determining the amount of retained austenite. Moreover, the strain rate has no significant effect on the bainite morphology.