Single-pass severe plastic forming of ultrafine-grained plain carbon steel

We developed an extrusion process with a cross-sectional area reduction as ‘single-pass severe plastic forming (S2PF)’ process for producing ultrafine-grained plain carbon steels. We investigated the microstructure and mechanical properties of fine-grained 0.2% carbon steels extruded at 1100–600 °C. Ultrafine ferrite grains with a grain size of 1.2 μm were generated at the surface of the materials extruded at 700 °C. The materials extruded at 800, 700 and 600 °C were investigated by scanning electron microscopy, electron backscattering diffraction analyses, tensile tests and compression tests. Extrusion at 700 °C, which is near the austenite–ferrite transformation temperature (Ar3), produced a material sample with a diameter of 5 mm, an average ferrite grain size of approximately 2 μm, a tensile strength of about 700 MPa, a uniform elongation of about 15% and a good cold-forging property.