Comparison of the Hardness-Toughness Relationship of Medium-Mn Steels after Q&T and Q&P Treatments*

In contrast to quenching and tempering (Q&T), with quenching to room temperature, quenching and partitioning (Q&P) usually applies quenching to a temperature between Ms and room temperature. To stabilize a sufficient amount of retained austenite (RA), carbon diffusion from martensite into austenite and a prevention of cementite formation takes place during the successive partitioning step. Larger amount of RA, and its transformation into martensite during plastic deformation, provides Q&P treated steels with an enhanced combination of strength and ductility. In this investigation, the effect of different Q&T and Q&P treatments on the hardness-toughness relationship was determined. These results are compared with the RA contents and mechanical properties provided by tensile testing. The obtained results clearly demonstrate that the optimum parameters for strength and ductility do not match with the best combinations of hardness and toughness. Furthermore, the stability of the RA plays an important role in the understanding of toughness properties of the investigated Q&P steels.