Abstract
The complex strain hardening behaviors of dual phase (DP) steel are subjected to the heterogeneous microstructures. The current work aims to predict the strain hardening behaviors of ferrite-martensite DP steel, focusing on the effects of heterogeneous microstructure on mechanical properties. The flow stress of material was calculated based on the dislocation-based work-hardening model with considering the multi-boundaries hardening. The ferrite-martensite phase boundary percent and grain shape factor were selected as the heterogeneous feature parameters, which were introduced into the new proposed model. The theoretical calculated stress-strain responses were verified with experimental results using the tensile test. The model with the boundary strengthening consideration has more accurate results. The parameter effects of ferrite-ferrite boundary (FFB) spacing, ferrite-martensite boundary (FMB) percent, and grain shape factor on the flow stress-strain curve were researched.
Highlights
Dual phase (DP) steels have been great development due to the good mechanical performance that could meet the requirements for the increased formability and weight reduction in automotive industry simultaneously [1]
Ferrite-martensite DP steels exhibit a superior combination of good strength and ductility [2], which is characterized by a microstructure consisting of hard martensite islands embedded in a relatively soft ferrite matrix
A mixed model based on the dislocation theory was developed to predict the strain-hardening behaviors of DP steel under uniaxial tension
Summary
Dual phase (DP) steels have been great development due to the good mechanical performance that could meet the requirements for the increased formability and weight reduction in automotive industry simultaneously [1]. In 1970, Ashby studied the deformation and work-hardening mechanics of dual-phase materials based on the both dislocation densities [27]. The ferrite matrix was divided into two regions considering with the boundaries hardening to predict the material flow stress [31]. The stress of ferrite phase, ferrite-martensite boundary (FMB) layer and martensite phase have been defined to predict the overall stress-strain curve considering the GNDs effects [32]. The microstructure characteristics and stress-strain models have been studied to explain the strain-hardening behaviors. The hardening model of DP steel considering with the grain morphology parameters including grain shape factor, martensite grain-boundary coverage ratio, and boundaries strengthening have rarely been reported. Further studies about the strain hardening model of DP steels taking grain morphology and boundary hardening into account under uniaxial tension are still necessary. The effects of boundaries strengthening and microstructural parameters on the work hardening behaviors of DP steel were investigated
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