Modelling the effect of carbide population and bainitic grain size on the fracture toughness of three forged low alloy steels

Fracture toughness of three low alloy quenched and tempered bainitic steels with similar chemical compositions but different manufacturing routes have been characterized in the Ductile to Brittle Transition (DBT) domain. One of these materials exhibits a much larger DBT temperature than the two other materials. The essential microstructural particularity of this material is its grain size, twice larger than the one of the two other materials. The Microstructure Informed Brittle Fracture model (MIBF) is modified to integrate grain size effects into the definition of the critical size of carbides used to compute cleavage initiation probability. The modified model predicts fairly well the different DBT temperatures of the three materials.