Effect of Tempering Conditions on Inhomogeneous Deformation Behavior of Ferrite–Martensite Dual-Phase Steels

Inhomogeneous deformation in DP steel has been investigated by SEM-EBSD method and high-precision markers drawn by electron beam lithography. Particular emphasis is laid on the effects of initial hardness of martensite on the development of inhomogeneity in ferrite during tensile deformation. The hardness of each phase in DP steels has been examined using a Berkovich-type indenter. Difference of the hardness between ferrite and martensite in the specimen tempered at 423K was larger than that tempered at 673K. Changes of local orientation obtained by SEM-EBSD method inside the ferrite in the steel tempered at 423K was more noticeable than that tempered at 673K. In addition, we employed a high-precision marking method using electron beam lithography in order to measure the local displacement. Not only the equivalent plastic strain in ferrite but also the one in martensite were obtained by using the method due to tensile deformation. It is clarified that the hardness of martensite effects the development of deformation inhomogeneity in both of ferrite and martensite. On the basis of results, the influence of the characteristic of deformation inhomogeneity on the mechanical property of the DP steels is discussed.