TRANSFORMATION KINETICS OF BAINITE DURING ISOTHERMAL HOLDING AND CONTINUOUS COOLING.

Abstract

The steel used was a high carbon and high chromium bearing steel (JIS SUJ 2). The overall isothermal bainite transformation kinetics are well expressed by a Johnson-Mehl type equation. The transformation rate decreased with increase in the austenite grain size. Transformation kinetics and optical microscope observations suggest that the nucleation site of bainite was both on the grain boundaries and inside the austenite grain. Comparison of the observed cooling transformation kinetics with that predicted from data showed that the transformed fractions were additive in bainite transformation.