Microstructure Informed Modelling of Ductile-to-brittle Transition in Ferritic Steels

The embrittlement of reactor pressure vessel (RPV) steel has been a great concern of the nuclear industry. Macro-segregated areas of carbon, alloy elements and impurities occur due to uneven solidification rates at different locations during the heavy forging process. These heterogeneities can lead to significant variations in fracture toughness in the Ductile-to-Brittle Transition (DBT) region. To quantitatively assess the safety of RPV, advanced micromechanical tools combining crystal plasticity and the local approach to fracture (LAF) are developed. This multiscale approach is applied to laboratory steels with different segregation levels chemically representative of actual RPV components. Simulation results demonstrate that the current approach is capable of predicting the shift of the DBT zone and the statistical scatter of fracture toughness with the variation of alloying elements. Results give insights into factors affecting fracture properties. Comparisons to phase field damage methods and new model prospects towards more accurate predictions are also discussed.