Towards the microstructure design of DP steels: A generic size-sensitive mean-field mechanical model

An original mean field composite model able to explain and quantify the tensile behavior of as-quenched dual phase (DP) Ferrite-Martensite steels based on the relevant microstructural parameters (grain size, phase fractions and composition) is presented. The model is unique in that it is applicable to microstructures ranging from fully ferritic to fully martensitic. This generic nature makes it a powerful tool for both alloy and microstructure design and for sensitivity studies over the entire range of martensite fractions. The model is based on a detailed understanding of the hardening mechanisms of the individual constituent phases and their interactions. Special attention is paid to the complexities arising from the coupling between grain size, phase fractions and local compositions of the phases, most notably the local carbon content in martensite (dilution effect). The few fitting parameters that are required have been adjusted on a database of more than 60 tensile curves extracted from the literature.