Microstructure and properties of a low-carbon steel processed by equal-channel angular pressing

An ultrafine-grained low carbon steel (Fe-0.15 wt.% C-0.52 wt.% Mn) was fabricated by equal channel angular pressing (ECAP) at room temperature by pressing for up to a maximum of 10 passes using route C. There was an elongated substructure with a width of ∼0.2-0.3 μm after 10 passes of ECAP and the corresponding tensile strength was >1200 MPa. It is shown that subsequent annealing for 1 h at 773 K, which is below the recrystallization temperature of ferrite, leads to equiaxed grains with a size of ∼0.3-0.4 μm, an increase in the tensile elongation and a strength above 1000 MPa. Annealing for 1 h at 873 K, which is above the recrystallization temperature, gives a recrystallized equiaxed structure of fine grains with an average grain size of ∼7 μm, a strength of <500 MPa and stress-strain curves similar to those anticipated for a low-carbon steel.