Thermomechanical Behavior of Biocompatible Austenitic Stainless Steels during Simulated Torsion Tests

The thermomechanical behavior and the microstructural evolution during the hot deformation are important aspects of metal alloys during hot forging and rolling processes. Here, the correlation between dynamically recrystallized grain size (d_DRX), steady-state stress (σ_ss) and Zener–Hollomon (Z) parameter is investigated according to the Universal Derby–Ashby relationship. Specimens of a UNS S 31673 and a UNS S 31675 steels, used in the manufacture of orthopedic implants, were subjected to continuous isothermal torsion tests. A strain of 3.0 and strain rates of 0.01, 0.1, 1.0 and 10 s⁻¹ at temperatures of 1000, 1100 and 1200 °C, were employed. The results showed that the competition between the hardening and dynamic softening (i.e., recovery and recrystallization) mechanisms, as depicted by the flow curves, agreed with the Derby relation. This observation is also a consequence of the variation in the stacking fault energy (SFE) with the applied strain. Additionally, the influence of the hot deformation parameters on the shape of the curves and the grain refinement is governed by the balance between these thermally activated mechanisms.