Physical modelling of microstructure and mechanical properties of dual-phase steel

The control of microstructure through physical models is of great interest in the development of new processes and products. Because microstructure results mainly from phase transformations occurring during the manufacturing process, modelling of this phenomenon is of great importance. Among the different hardening mechanisms of steels (solid solution, precipitation, grain size, second phase...) the dispersion of a hard second phase in the ferritic matrix is one of the best methods to optimise the strength/ductility ratio. To achieve weight reductions and fuel saving in vehicles, materials designers have concentrated on Dual-Phase steels (DP) containing ferrite and martensite phases which can be obtained by relatively simple heat treatments. This paper deals with the combination of two types of models developed at IRSID, with the aim of prediction of final properties of hot rolled dual phase steels. The microstructure/mechanical properties relationships in DP steels are first presented. A physical approach for austenite decomposition into grain boundary ferrite for C-Mn steels is described. Finally, the combination of both models is used to predict the effect of process parameters on microstructure and on the mechanical properties.