In Situ Observation of the Peritectic Reaction and Transformation in a Commercial HSLA Steel

In situ experiments have been performed to investigate the peritectic reaction and transformation in a commercial HSLA steel. The characteristic temperature and interface migration behavior were recorded during the peritectic reaction and transformation were recorded during the cooling. The in situ observed results indicated that the austenite phase (gamma) was observed to nucleate at the interface of the liquid and primary delta-ferrite phases. The intermediate gamma phase propagated along with the liquid/delta-ferrite interface and gradually isolated the liquid and primary delta - ferrite phases. Subsequently, the annular gamma phase laterally grew toward the liquid and delta phases. Moreover, the occurrence of the peritectic reaction turned into a lower temperature as the cooling rate increased. In the peritectic transformation, the gamma phase thickened toward both the liquid side and primary delta-ferrite side. The interface migration velocities during the peritectic transformation were obtained by measuring the migration distances of two interfaces versus time. The migration velocity of austenite/delta-ferrite (gamma/delta) interface was significantly higher than that of liquid/austenite (L/gamma) interface. Furthermore, an increase in the cooling rate accelerated the migration velocities of gamma/delta and L/gamma interfaces during the peritectic transformation.