In-situ Observation of Ferrite Plate Formation in Low Carbon Steel during Continuous Cooling Process

In-situ observation of austenite-to-ferrite transformation in low carbon steel was conducted with a laser scanning confocal microscope. Development and kinetics of ferrite plates during continuous cooling process were studied. It was in-situ observed that the ferrite plates nucleated at either austenite grain boundary or allotriomorphic ferrite, and grew with keeping the Kurdjumov–Sachs orientation relationship with prior austenite. Surface relief was induced by the formation of ferrite plate. When the ferrite plate nucleated at pre-existing grain boundary ferrite, gradual change in growth direction by the sympathetic nucleation was confirmed both by the observation and EBSP analysis. Temperature dependency of the observed growth rates of the plates was in a good agreement with the Zener–Hillert model, which indicates the growth is controlled by the diffusion of carbon.