Direct Observation of High-temperature Phase Transformations in Steel: Delta-ferrite to Austenite Phase Transformation

During continuous casting of steel, the delta-ferrite to austenite phase transition occurs following solidification. It is of great industrial significance to gain a better understanding of the nature of this reaction because product quality is in large measure determined by events occurring during and shortly following solidification. Moreover, the exact way in which delta-ferrite transforms to austenite may influence the subsequent transformation of austenite to ferrite, by which much of the mechanical properties of the steel is determined. Relatively little attention has been devoted to the delta-ferrite to austenite phase transition in the past, in part because of the difficulty of making in-situ observations at the high temperature. The recent development of high-temperature Laser-Scanning Confocal Microscopy has provided new opportunities to observe in-situ high temperature phase transformations and this technique has been employed in the present study. The analysis should impact on some aspects of the steel production industry. High-temperature LSCM provides new opportunities for research in casting technology as well as high-temperature phase-transformation studies.