The austenite/ferrite front migration rate during heating of IF steel

The austenitization of interstitial free (IF) steel was investigated through real time imaging of evolving surface relief structures through a hot-stage confocal scanning laser microscope. Nucleation was observed at grain edges but site saturation did not occur. As expected the, the migration rate was found to be controlled by an interface reaction and the rate was, within the experimental errors, nearly indistinguishable between IF steels, pure Fe and previously reported rates for pure Fe with activation energies between 174-180 kJ/ mol. There was no apparent effect of solute drag caused by the trace solute elements in the IF steel, but the non-metallic oxide and nitride particles present in the IF steel appeared to impede the front migration and caused it to become jagged in appearance.