Abstract: The transition from columnar to equiaxed grains during hot deformation at various strain rates has been studied in an as-cast medium-carbon low-alloy steel. Experiments were carried out at 1200 °C and 0.25 s-1 to 2 s-1 strain rate range using a Gleeble 3800® thermomechanical simulator. Microstructural analysis was performed using EBSD to quantify the internal misorientation of grains. Mathematical calculation of the data indicates that highest fraction of equiaxed grains are developed at the lowest strain rates. Conversely, when the strain rate is increased, columnar grains are dominant. We correlate the experimental results with the influence of deformation parameters on carbon diffusivity, and its impact on the columnar to equiaxed transition. It is found that an increase in strain rate increases the diffusivity of carbon atoms; however, the diffusion distance of carbon is reduced significantly, which is the mechanism responsible for decreased equiaxed grain formation at higher strain rates.
Authors: K. Chadha, M. Jahazi, and John G. Spray
Keywords: Hot Deformation, Equiaxed grains, As-cast structure, EBSD