Effects of martensite fraction on tensile properties and inhomogeneous deformation of microstructures in dual-phase steels have been investigated by TEM, SEM-EBSD and strain mapping using high-precision grid markers drawn by electron beam lithography. As is well known, when volume fraction of martensite is increased from 25% to 75%, yield and tensile strengths markedly increase while elongation decreases. It was found by EBSD that the average value of kernel average misorientation in ferrite increase with martensite fraction. Strain mapping using the marker method showed that both equivalent plastic strains of ferrite and martensite increase with martensite fraction, where it is to be noted that the strain increase of martensite is larger than that of ferrite, suggesting that the stress redistribution between ferrite and martensite is enhanced with increasing the martensite fraction.
