Effect of martensite volume fraction on stress triaxiality and deformation behavior of dual phase steel

•Strain partitioning between ferrite and martensite during straining.•Local deformation in ferrite is constraint by adjacent martensite.•Stress triaxiality buildup within two phase microstructure.•Stress triaxiality band increases with increasing martensite volume fraction.•Uniform elongation of dual phase steel reduces with increase in tensile stress triaxiality.

Strain incompatibility among softer ferrite matrix and harder martensite phase arises during tensile straining due to difference in the flow characteristics of two phases. Strain incompatibility between ferrite and martensite phases during tensile straining results strain partitioning, inhomogenous deformation and finally deformation localization. The local deformation in ferrite phase is constrained by adjacent martensite islands which results in local stress triaxiality development. As martensite distribution varies within the microstructure, the stress triaxiality also varies in a range within the microstructure. Effect of martensite volume fraction on stress triaxiality and tensile deformation behavior on dual phase steels are examined in the current investigation by conducting rigorous finite element study on representative volume elements. The investigation reveals that with increasing martensite volume fraction the band of stress triaxiality distribution increases (i.e. locally stress triaxiality approaches towards plane strain condition) and as a consequence uniform elongation reduces.