Strain Partitioning of Step Quenched Dual Phase Steels in Tensile Deformation

The strain partitioning behavior of step quenched dual phase steels with martensite volume fraction of 33.8% or 58.3% was studied in different tensile deformation degrees using digital image correlation (DIC) method of sub-micron scale. The results show that the strain partitioning behavior was similar for both dual phase steels in different deformation degrees; the strain distribution was quite inhomogeneous, especially when the deformation degree was increased; the inhomogeneity of strain partitioning behavior between ferrite and martensite was more pronounced for dual phase steel with less martensite. There were deformation bands with intense strain in the micro area, which mainly distributed in ferrite regions, especially in narrow ferrite bands between martensite. There were also few deformation bands in martensite and along the phase interfaces, and the deformation bands along the phase interfaces increased in number when the volume fraction of martensite was small. The probability of deformation bands crossing martensite was larger for dual-phase steel with large volume fraction of martensite.