Excellent Strengthening of Low-Carbon Steel by Severe Free-End Torsion

In this work, the effects of free-end torsion on microstructure and tensile property of low-carbon steel were investigated in detail. Low-carbon steels exhibited exceptionally high yield strength through severe torsion deformation. Such high hardening effect was mainly attributed to the severe lattice distortion, high density of dislocations and the change in grain shape. Moreover, a gradient deformation structure can be introduced by torsion deformation. The gradient-structure can generate a high hetero-deformation induced strengthening, which can increase the strain hardening capacity and remain high plasticity/toughness. Therefore, with increasing torsion angle from 700 to 2800 deg., the uniform elongation and the peak strength were largely enhanced. After twisting 2800 deg., yield strength and peak strength can achieve 524 MPa and 675 MPa, respectively, and good tensile elongations (epsilon(f) = 9.6%, epsilon(u) = 7.4%) are remained.