Effect of austenite grain size on the transformation kinetics of upper and lower bainite in a low-alloy steel

The effect of austenite grain size on the continuous cooling transformation kinetics of upper and lower bainite in a low-alloy steel has been investigated using a dilatometer. The transition temperature between upper and lower bainite is almost constant (430 °C) irrespective of the grain size. The transformation rate of upper bainite increased with a decrease in grain size. The instantaneous transformation rate of lower bainite at each volume fraction is not related to the austenite grain size.