Ultrafine grained microstructure was produced by repetitive deformation using the cold side-extrusion method from carbon steels. The side-extrusions with lateral pressure were repeated up to 10 passes without rotation. Each sample was uniformly deformed by the side-extrusion, and the equivalent strain was 1.15 after a single pass of the side-extrusion. After 10 passes of side-extrusion an ultrafine grained steel with a tensile strength of over 1000 MPa a grain size of 0.5μm × 0.2 μm was developed for the ultra low carbon steel. The uniform elongation in tensile test for the steels after repetitive side extrusions was very small, but the cold formability was very good. By the heat treatment, the uniform elongation became larger.
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