Non-isothermal austenite formation behavior in an interstitial free steel with different ferrite microstructures

The ferrite-to-austenite transformation in an interstitial free steel was investigated in terms of the initial morphology and grain size of ferrite. The reverse transformation occurred at a lower temperature in the order: tempered massive ferrite, as-quenched massive ferrite, polygonal ferrite and coarse-grained polygonal ferrite. While the transformation rate of polygonal ferrite smoothly increases and decreases again during continuous heating, there were serrations on the transformation rate for massive ferrite, probably due to different nucleation behaviors.