Development of in situ microstructure observation technique in steel

In situ observation of microstructure change at high temperature is valuable technique to investigate the phase transformation, grain growth, and precipitation phenomenon in steels. Although scanning and transmission electron microscopes are utilized for the in situ observation, these techniques have some serious problems represented by a surface diffusion effect and a thin foil effect. A new technology based on the focused ion beam system has been developed to overcome these subjects. A bulk microstructure required was newly obtained at high temperature by the FIB fabrication, and the microstructure changes with annealing were observed, in which a considerable surface artificial effect seems to be decreased. Using this technique, the intra-granular ferrite transformation process has been investigated, resulting in a strong proof supporting the Mn depletion effect model for the transformation.