Constitutive analysis of stress-strain curves in dynamic softening of high Nb- and N-containing austenitic stainless-steel biomaterial

High N-containing austenitic stainless steels have long been used as materials in orthopedic implants. For almost three decades, research has shown that ASTM F-1586 steel is an alternative for orthopedic applications involving severe loads and long implant survival rates in the human body. However, several studies have detected impaired mechanical strength of prostheses during use as a result of manufacturing processes. In this research work, the dynamic softening of this material is characterized based on a constitutive analysis of the stressestrain curves under conditions resembling those of industrial manufacturing, obtained by continuous isothermal hot torsion tests at different temperatures (900 degrees C-1200 degrees C) and strain rates (0.01-10s(-1)). The results indicate that the hot deformation apparent activation energy (Q(def) = 594 kJ/mol) is high compared to other types of 300 series stainless steel, as are the ratios between critical (sigma(c)), peak (sigma(p)), steady state (sigma(ss)) and saturation (sigma sat) stresses: sigma(o)/sigma(p) = 0.69, sigma(c)/sigma(p) = 0.94, sigma(ss)/sigma(p) = 0.68 and sigma(sat)/sigma(p) = 1.01. These high values suggest competition between the mechanisms of work hardening (WH), dynamic recovery (DRV) and dynamic recrystallization (DRX), with delay in the onset and progression of DRX kinetics, significantly affected by the moderate stacking fault energy (gamma(sfe) similar to 68.7 mJ/m(2)), solute atoms (Nb,N) and by fine Z-phase precipitates (CrNbN) at the grain boundaries, which favor softening with intense DRV. Thus, as can be seen, the parameters of WH (h), DRV (r) and DRX (t(0.5), n) determine the shape of the stressestrain curves. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This research characterizes the dynamic softening behavior of high N-containing austenitic stainless steel under conditions resembling industrial manufacturing. The results indicate that the material's behavior is influenced by competition between work hardening, dynamic recovery, and dynamic recrystallization mechanisms, as well as stacking fault energy and grain boundary microstructures.