Constitutive Relations Analyses of Plastic Flow in Dual-Phase Steels to Elucidate Structure–Strength–Ductility Correlations

The structure–strength characterization is typically performed by correlating the structure with x-ray, electron, or atomic imaging devices to the bulk mechanical tensile parameters of yield stress and the plastic yielding response. The problem is that structure parameters embedded in the stress–strain data cannot be revealed without an analyzable constitutive relation. New functional slip-based constitutive formulation with precise digital fitting parameters can replicate the measured data with at least two loci. Thus, this study examines the possibility of identifying the mechanical response as a result of the various microstructure components. The key parameter, the mean slip distance, can be calibrated from the initial work-hardening slope at 0.2% strain from which all the fit parameters can be determined. In this process, a newly derived friction stress is defined to separate the yield phenomenon from the plastic strains beyond yield-point elongation. This methodology has been applied to dual-phase steel specimens that resulted in excellent predictive correlations with prior structure-strength characterization. Hence, the structure–strength–ductility changes resulting from processing conditions can be more precisely surmised from mechanical testing. Thus, a method to delineate the nanostructure evolution with deformation using mesoscopic mechanical parameters has been introduced.