In the last years a hot metallurgical topic has been the study of so-called third generation advanced high strength steels (AHSS) for automotive applications. Such steels often contain a complex microstructure of tempered martensite (for strength) and retained austenite (providing ductility through strain-induced transformation). Despite significant progress, a deep understanding of the relationship between microstructure and properties remains to be fulfilled.

The current contribution investigates the role of microstructure on mechanical properties in stainless AHSS, produced by quenching and partitioning (QP) treatments in a dilatometer. Such stainless steels possess the advantage of high hardenability, thus a wide range of retained austenite fractions could be achieved. As an efficient sensor for indicating mechanical properties, macro hardness tests were used to elucidate the effect of retained austenite fraction, as measured by a vibrating sample magnetometer. The results and trends obtained have been compared to the literature on AHSS carbon steels (1st generation dual phase and 3rd generation QP), highlighting similar or different behaviour. Finally, the significance of using macro hardness for estimating tensile strength in retained austenite steels is discussed.