Constitutive Analysis of the Mean Flow Stress of a Nb- and N-Bearing Austenitic Stainless Steel Biomaterial

The correlation between hardening and softening in an ASTM F-1586 stainless steel used as biomaterial was investigated by means of hot torsion simulations. Multi-pass deformation under continuous cooling was employed to simulate industrial hot rolling. Samples were subjected to 17 deformation passes of strains of 0.20 and 0.30, strain rate of 1.0 s−1 in a temperature range of 1250 to 930 °C. Interpass times (tp) of 5.0, 10, 20, 40, and 80 s were used. The obtained results showed direct dependence of the mean flow stress (MFS) and all applied thermomechanical parameters. The work hardening rate associated with the degree of stress accumulation (Δσ) inhibited the metadynamic recrystallization. This led to the variation of the non-recrystallization temperature (Tnr), associated with intense static recovery in the material. From the experimental data, a constitutive function of the mean flow stress (MFS) obtained through multiple nonlinear regression technique was proposed. The study aimed to have a better understanding of the physical metallurgy behind the thermomechanical behavior of the steel under a multi-pass process. The results allowed to monitor the recrystallized fraction (X) and the grain size (d) during the simulated conditions.