Interface Motion in Phase Transformations. Bainite Transformations in Hypoeutectoid Steels

摘要

Kinetic and structural aspects of bainite formation were studied by stepped transformation experiments. Growth of lower bainite stops if the temperature is raised to the upper range and upper bainite either stops growing or grows at a rate substantially below that of lower bainite when the temperature is reduced suddenly to the lower range. It is concluded that the internal structural differences which characterize upper and lower bainite exert a significant influence on the rate at which these products develop. In the steels studied in this investigation, lower bainite plates thicken from one side only. These plates exhibit a substructural unit oriented at an angle to the growth direction and these units appear to nucleate at the immobile side of the plates. Edgewise growth rates measured on the hot stage thus may reflect primarily the rate of nucleation of these substructural units. A similar situation may prevail in the growth of upper bainite needles. (Author)