A NEW RELATIONSHIP BETWEEN THE FLOW-STRESS AND THE MICROSTRUCTURAL PARAMETERS FOR DUAL PHASE STEEL

A theoretical model for predicting the flow stress of dual phase steel has been proposed based on the Ashby work hardening theory and the dislocation pile-up model. An expression for the relation between the flow stress and the microstructural parameters has been derived. This model takes into account both effects of ferrite grain size and martensite island size as well as the martensite volume fraction on the flow stress, which demonstrates that the flow stress dependence of ferrite grain size can be generally expressed in the form of the Hall-Petch relation. In terms of dislocation theory, the flow stress depends primarily on the geometrically necessary dislocation density nearby the ferrite/martensite boundaries and the statistically stored dislocation density in the ferrite matrix. Very good agreements have been obtained when the proposed relationship was applied to predict the experimental true stress-true strain curves of a 1020 dual phase steel and a spheroidized carbon steel.