The development of an ultrafine grain size during repeated shear deformation of side extrusion of ultra-low-carbon steel with an initial grain size of approximately 150 μm and a tensile strength of 200 MPa was investigated. Experiments were carried out at room temperature and at a low extrusion speed of 2 mm min-1. Repeated side extrusions with lateral pressure were carried out for up to ten passes for the specimen extruded without rotation (route A). Uniform shear deformation was obtained by the side extrusion with the lateral pressure and an equivalent strain after a single side extrusion was 1.15. After ten passes of the side extrusions, an ultrafine-grained steel with a grain size of 0.5 μm x 0.2 μm was realized and the tensile strength was over 1000 MPa.
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