Influence of inhomogeneous deformation on strengthening behaviours of ferrite-martensite dual phase steels

Tensile properties and inhomogeneous deformation of dual phase steels were analyzed. The proportionality of stress to the volume fraction of martensite (f) had a transition at f = 0.3. Three stage deformation was found in the strain hardening rate of dual phase steels when f was less than 0.3. Degree of stress and strain inhomogeneities was visualized by relating the in situ stress-strain states of ferrite, martensite and their composite to each other. Martensite deforms elastically before the uniform strain in the case of f < 0.25, while it undergoes plastic flow before the uniform strain with larger amount of martensite. It was concluded that the tensile properties of dual phase steels were influenced largely by the plastic deformation of martensite phase