A bainite transformation kinetics model and its application to X70 pipeline steel

A new continuous-cooling kinetics model for bainite transformation based on diffusionless-displacive mechanism is proposed in this work to predict bainite transformation in the coarse-grained heat-affected zone (CGHAZ) of X70 pipeline steel. The Gleeble-3500 thermal–mechanical simulator was used to analyze the bainite transformation process in CGHAZ of X70 pipeline steel. The features of bainite transformation predicted from the proposed model were compared with the values measured from experiment, and the results show that the predicted bainite volume fraction and transformation velocity are in good agreement with the measured values. This indicates that the proposed kinetics model used to predict the bainite transformation process in the CGHAZ of high-strength low-alloy steel is reasonable. The model could be widely used in prediction of bainite transformation with high cooling rate, such as in welding CGHAZs.