Effects of shear deformation via torsion on tensile strain-hardening behavior of SCM415 low-alloy steel

Abstract

The effect of shear deformation via torsion on tensile strain-hardening behavior of SCM415 low-alloy steel was investigated. Hot-rolled SCM415 rods were machined into round tensile-test specimens based on ASTM E8M. SCM415 round tensile specimens were subjected to shear deformation using a free-end torsion testing machine at a constant rotational speed of 0.1 rpm. The specimens were torsionally deformed at room temperature to four different angles: 0.314 rad, 0.628 rad, 1.256 rad, and 2.512 rad. Tensile tests of torsionally deformed specimens were then carried out. The engineering stress-strain curves indicated that yield strength and ultimate tensile strength increased while ductility decreased with a higher degree in shear deformation via torsion. From true stress-strain curves generated using engineering stress and strain values, it was found that the strain hardening rates were lower in specimens with a higher degree of shear deformation via torsion. A power law was applied to curve fit the true stress-strain data in the uniform plastic deformation region. The strength coefficient and strain hardening exponent were lower in specimens with a higher degree of shear deformation via torsion. The decrease in strain hardening exponent and work hardening capacity of specimens with a higher degree of shear deformation via torsion was presumably caused by a combination of high dislocation density and grain refinement after severe plastic deformation.