Kinetics of bainite transformation in steels

The main kinetic features of the formation of bainite are discussed, firstly in relation to two incompatible hypotheses for the growth mechanism of bainitic ferrite. One is based on diffusionless growth of bainitic ferrite but diffusional growth of Widmanstatten ferrite. The other is based on the assumption that there is only one kind of acicular ferrite and it grows under simultaneous diffusion of carbon into the interior of the parent austenite. The kinetics of the first stage of bainite formation, the growth of acicular ferrite, is treated in detail because it has been subject to the more intensive research. The kinetics of the reactions by which cementite forms and the subsequent reactions, by which the transformation to bainite is completed, have been subject to less research.