KINETICS MODELLING OF ISOTHERMAL BAINITE TRANSFORMATION IN LOW CARBON MULTI-MICROALLOYED STEEL

摘要

In this work, the isothermal bainite transformation in a low carbon multi-microalloyed steel was investigated using a dilatometer. Two different transformation behaviors were identified according to the measured dilatometric curves. The variation of transformation mechanism was explored based on the microstructural observation and the change of the Avrami exponent with the holding time and isothermal temperature. For example, the solute drag effect is mainly responsible for the transformation stasis phenomenon at the first stage of the abnormal reaction curve. A physically-based model was proposed to describe the normal bainite formation kinetics curves on the basis of the modification of the Johnson-Mehl-Avrami (JMA) equation. The transformation mode is considered as the site saturation of nucleation and interface controlled growth under the large undercooling condition. Comparison between the calculation curves and the experimental data in this experimental steel gives a very good agreement.