The aim of my study is to improve the fracture behavior and to enhance the strength of structural steels by controlling the deformation behavior. Accurately measuring the macro- and micro-deformation in terms of strain and strain rate is one key point of the study. Strain and strain rate measurement systems have been developed by using digital image correlation (DIC) technique which are available to in-situ measure/observe the deformation process at a macroscopic scale and a microscopic scale. One developed DIC measurement system for the microscopic stain is shown in the above figure. By using this system, micro-strain distribution within grains in tensile process or bending process can be measured. From the experimental results, information on the stress concentration (position, magnitude), interaction between grains, evolution of micro-strain and so on is available. Combined with the observation of microstructure and fracture mode by the electron back scattered diffraction, scanning electron microscope and optical microscope, the correlation of micro-deformation behavior with microstructural parameters (grain size, orientation, etc.) and fracture mode is revealed.