Improved elongation in high-strength low-alloy steel by non-monotonic tensile loading and dislocation-based phenomenological plasticity modeling

In this study, three types of tensile testing of high-strength low-alloy steel were conducted as (a) Let the cross-head monotonically move upward. (b) At every 1 mm of elongation after the initial 2-mm elongation, unload and hold the stress at 0 for 1, 5, or 10 s and then reload. (c) At every 1 mm of elongation after the initial 2-mm elongation, hold cross-head displacement for 1, 5, or 10 s and then reload. Obtained stress–strain curves revealed that the uniform and total elongations were greater when the time between the unloading/holding and reloading was longer. An electron back-scattering diffraction measurement clarified that, in contrast to monotonic tensile testing, 〈111〉 (slip direction) was not aligned in the tensile direction and as-rolled alignment of 〈110〉 remained unchanged even after the elongation reached the uniform elongation in non-monotonically loaded specimens. This texture difference is a possible reason for improved elongations. A dislocation-based phenomenological plasticity model was also established to explain the improved uniform elongation. A low-temperature creep model was adopted to describe the change after unloading/holding. The model successfully reproduced the stress–strain relationship in non-monotonic loading and the improved uniform elongation.