The microstructure of dual phase steels could be compared with a composite composed of a matrix of ferrite reinforced by small islands of martensite. This assumption was used in several attempts to model the mechanical properties of dual phase steels. However, recent measurements showed that the properties of the ferrite phase changed with distance from the martensite grains. These measurements showed that the grains of the ferrite phase were harder in the vicinity of martensite grains. As a consequence of this local hardening effect, the ferrite phase had to be considered as an inhomogeneous matrix in modelling dual phase steels. This experiment inspired the idea that local hardening was caused by geometrically necessary dislocations. The idea was investigated experimentally and numerically in the present analysis, which for the first time leads to good agreement with experimental observations of the mechanical stress–strain behavior.

Experimental and Numerical Study on Geometrically Necessary Dislocations and Non-Homogeneous Mechanical Properties of the Ferrite Phase in Dual Phase Steels. J.Kadkhodapour, S.Schmauder, D.Raabe, S.Ziaei-Rad, U.Weber, M.Calcagnotto: Acta Materialia, 2011, 59[11], 4387-94