Semisolid extrusion of low-carbon steel

The semisolid state behavior and semisolid extrusion properties of low-carbon steel were investigated, focusing on the possibility of clarifying a semisolid-forming process. First, the cooling curve of low-carbon steel is assessed by thermal analysis, so as to clarify the semisolid temperature range. The microstructure of the hot-rolled bar obtained at the semisolid temperature is the globular structure similar to those of aluminum and magnesium alloys. Then, to obtain a better understanding of the semisolid deformation behavior of the material, extrusion tests are carried out at various billet temperatures and cooling conditions at the die exit. To prevent the temperature decrease of the billet, a graphite case and block surrounding the billet acted as an insulator in the extrusion tests. The mechanical properties and the microstructure of the extruded products are evaluated and discussed, i.e., the extrusion force in the semisolid state is less than half that of the hot extrusion. The distribution of chemical components, such as carbon, is measured in the radial direction of the cross section of the products. The room-temperature hardness of the as-extruded products shows a specific distribution from the surface to the center. The hardness at the center is approximately two times greater than that at the surface.