A theoretical model for the flow behavior of commercial dual-phase steels containing metastable retained austenite: Part I. derivation of flow curve equations

A semi-mechanistic model for predicting the flow behavior of a typical commercial dual-phase steel containing 20 vol pct of ‘as quenched’ martensite and varying amounts of retained austenite has been developed in this paper. Assuming that up to 20 vol pct of austenite with different degrees of mechanical stability can be retained as a result of certain thermomechanical treatments in a steel of appropriate low carbon low alloy chemistry, expressions for composite flow stress and strain have been derived. The model takes into account the work hardening of the individual microconstituents(viz., ferrite-@#@ α, retained austenite- γ _r, and martensite -α′) and the extra hardening of ferrite caused by accommodation dislocations surrounding the ‘as quenched’ as well as the strain-induced(γ _r→ α′) martensite. Load transfer between the phases has been accounted for using an intermediate law of mixtures which also considers the relative hardness of the soft and the hard phases. From the derived expressions, the flow behavior of dual phase steels can be predicted if the properties of the individual microconstituents are known. Versatility of the model for application to other commercial steels containing a metastable phase is discussed.