Influence of hybrid deformation processing on microstructural gradients and mechanical performance of AISI 1010 steel

In this work, the influence of combining severe cold rolling and pin-less friction stir–based surface thermomechanical processing on the microstructural gradients and mechanical performance of AISI 1010 low-carbon steel is systematically quantified. Results show that at the processed top surface, the elongated ferritic–pearlitic structure produced by rolling is fully replaced by dynamically recrystallized equiaxed ferrite grains, with the average grain size increasing from 0.32 ± 0.05 µm at 200 rpm to 1.62 ± 0.12 µm at 1400 rpm. In contrast, the mid-thickness and bottom regions largely retain the deformed rolling microstructure, with only partial recrystallization occurring at the highest rotational speeds. This gradient microstructure leads to a systematic reduction in hardness from the surface toward the core and a decrease in average hardness from 265.1 ± 13.4 HV0.1 at 200 rpm to 199.5 ± 15.6 HV0.1 at 1400 rpm. Tensile testing demonstrates that hybrid processing significantly enhances ductility and toughness at the expense of strength: elongation increases from 8.2% in the cold-rolled condition to 22.3% at 1400 rpm, while tensile toughness rises from 47.1 to 158.5 MJ/m³. Concurrently, the yield strength decreases from 899 MPa in the cold-rolled state to 661 MPa at the highest rotational speed.