In the case of metals, it is considered that the crystal grain refinement due to plastic deformation is caused by the operation of various slip systems in a grain. In order to understand the initial stage of the grain subdivision, a simple shear test was performed on a low-carbon-steel polycrystal having an average grain size of approximately 150 μm.

After the application of 10% shear, several regions having different slip lines were observed in a grain. The slip lines were explained by {110}<111> slip-system of body-centered cubic iron, and the operated Burgers vectors were estimated. The crystal orientations were different for the subdivided regions, and misorientation angles of the crystal rotation were approximately 10°. The rotation axes of the crystal rotation across the subdivided regions were determined. The rotation axes were almost perpendicular to either of the estimated Burgers vectors in the subdivided regions. The directions of the rotation axes are discussed.