Microstructural design in quenched and partitioned (Q&P) steels to improve their fracture properties

Quenching and partitioning (Q&P) is receiving increased attention as a novel heat treatment to produce advanced high strength steels (AHSSs) containing martensite/retained austenite mixtures, with desirable combination of strength, ductility and toughness. Despite the significant body of research on microstructure and mechanical properties of Q&P steels, there is still a significant lack of knowledge on the effect of complex microstructure on their mechanical performance. This work addresses the effect of microstructural architecture in multiphase Q&P steels on their fracture behavior at macro- and micro-scales. It is demonstrated that the RA volume fraction does not affect significantly the local fracture initiation toughness, whereas it can greatly improve the total crack growth resistance in Q&P steels. In addition, matrix conditions can play an important role in the fracture behavior of Q&P steels. Based on the analysis of the experimental results, a general recipe to tailor fracture properties of Q&P steels is proposed.