The Mechanical Behaviour and Microstructures of Interstitial Free Steel Strained in Monotonic or Cyclic Torsion at 1223K
The work hardening behavior of metals under cold cyclic or multiaxial deformation involves lower hardening rates than those caused by monotonic strain to the same total magnitude. The hardening is lower as the strain per cycle decreases. Similar studies under hot working conditions, for a limited number of cycles, also lead to lower hardening, as well as to changes in the shape of the flow curves and to delays in the initiation of Dynamic Recrystallization (DRX) and in the post-processing static softening kinetics. These results point to a decrease in stored energy caused by cyclic straining. A higher number of hot deformation cycles leads to lower steady state stresses (σ<sub>ss</sub><sup>r</sup>) than those corresponding to monotonic deformation (σ<sub>ss</sub>). Besides, DRX can be suppressed and replaced by Dynamic Recovery (DRV), and the successive cycles have been associated with the repeated build-up and disintegration of dislocation structures. The present research discusses the hot deformation of an IF steel in the austenitic temperature range, for monotonic torsion or a large number of reversed torsions with various strain amplitudes (Δε). It was confirmed that σ<sub>ss</sub><sup>r</sup> depends on the relative amplitude of the strain cycles (Δε/ε<sub>p</sub>, where ε<sub>p</sub> is the strain at the peak stress in the monotonic torsion of the material), and that lower values of Δε/ε<sub>p</sub> eliminate DRX, which is replaced by DRV. The ferritic grain size after deformation into the cyclic steady state stress depends on the value of σ<sub>ss</sub><sup>r</sup>, similarly to results in the literature for monotonic torsion of IF steels.
- ISIJ international
ISIJ international 46(5), 734-743, 2006-05-15
The Iron and Steel Institute of Japan