Construction of Phase Transformation Model for Heat-affected Zone of Steel Plate Welds and Toughness Prediction

For the purpose of making calculable the microstructure feature value required for predicting the Charpy absorption energy of the heat-affected zones (HAZs) of steel-plate welds with a brittle fracture model based on weakest link theory, a phase transformation model has been constructed on the basis of the phase transformation data on a quaternary model steel and the previously reported model formula. It has been confirmed that the phase transformation behavior of HAZs at various cooling rates can be reproduced by the model calculation for steel plates with different chemical compositions, mainly HT570 grade and HT780 grade steels. Calculations based on this phase transformation model have confirmed that the Charpy absorption energy of HAZ can be consistently predicted, and the calculated values agree well with the experimental results. In addition, the predicted transition curve of Charpy absorption energy corresponds to the experimental results in which the transition temperature shifts due to the difference in cooling rate. © 2021 Kobe Steel Ltd. All rights reserved.