Prediction of hot flow plastic curves of ISO 5832-9 steel used as orthopedic implants

Abstract

An austenitic stainless steel ISO 5832-9 used as a biomaterial was torsion-deformed over the temperature range of 1000-1200 °C and strain rates of 0.05, 0.1, 1.0 and 5.0 s -1 . The flow stress curves obtained showed two regions where firstly there is a rising on stress characterized as work hardening mechanism acting and secondly a decreasing in work-softening after a peak stress. The flow curves were modeled by adjusting the experimental data with Zener-Hollomom parameter to construct the constitutive equations that describe the plastic behavior in both regions. The first region was described until the peak stress, taking into consideration the competition between work hardening and recovery while the second one was described applying the softening time of 50% and the Avrami equation. In some hot deformation conditions the simulated curves showed good agreement with the experimental ones while in others conditions the simulated showed differences to experimental curves that was discussed and associated with other mechanisms that acted during hot deformation.

Plastic Instability in ISO 5832-9 High-nitrogen Austenitic Stainless Steel

“…Under these conditions one can see that the curves can be separated into three regions, according to their shape: (i) strain softening after the peak, leading the steady state to large deformations; (ii) continuous softening, with localized flow; and (iii) plane type flow curve where the stress hardly varies, with deformation showing intense dynamic recovery and reduction of the work hardening rate reaching a saturation stress. 20,21) As can be seen from the curves, the stress level increases with increasing strain rate at a given temperature, analogously with the decrease in temperature at a constant strain rate. On the other hand, the evolution of the amount of deformation presents different behaviors.…”

“…At high temperatures, the decrease in stress between the peak and steady state stress was relatively minor, while the decrease after the peak was gradual and relatively greater at intermediate temperatures, where the extent of softening promoted by dynamic recovery after the onset of dynamic recrystallization clearly affected the shape of the flow curve. 21) As can be seen, at high temperatures and low strain rates, particularly at 0.05 s -1 , the shape of the initial part of the plastic flow curves differs from the others. Plastic flow starts at stress levels very close to the values of peak stresses, generating a region of plastic deformation with a relatively low work hardening rate.…”

“…This typical aspect of dynamically recrystallized material is due to the generation of dislocations, twinned crystals and deformation bands when the material is hot deformed, increas- ing its mechanical strength while reducing the mobility of the dislocations. 20,21) This ISO 5832-9 austenitic stainless steel alloy shows moderate SFE with a lower annihilation rate than generation rate; hence, there is a heterogeneous dislocation pile-up that favors the nucleation of new grains.…”

Softening Mechanisms of the AISI 410 Martensitic Stainless Steel Under Hot Torsion Simulation

“…The coefficient h contributes to increase the level of stress during deformation on the upward slope of the curve, modifying its profile, particularly at low temperature and high strain rates (High Z). The literature reports that in this stage, there is formation and increased density of dislocations, which accumulate and interact, entrapping and forming sub-grains with reduced mobility, requiring a higher stress level to trigger greater plastic deformation [20][21][22] . However, the operations of thermally activated mechanisms, such as scaling and crossslip, favor the rearrangement and elimination of these defects, enabling the formation of substructures, reducing the work hardening rate parabolically and increasing the coefficient of dynamic recovery (r), as indicated in Figure 7.…”

Surface morphology andin vitrobioactivity of biocompatible hydroxyapatite coatings on medical grade S31254 steel by RF magnetron sputtering deposition

“…This is owing to their excellent mechanical properties and comparative low cost [1][2]. Lately, newer generation of steels with superior corrosion resistance and mechanical properties are being studied [3][4][5][6][7]. For orthopaedic implants ISO 5832-9 SS is being used, in comparison to F138-92 SS as it does not undergo pitting corrosion [8][9][10][11][12].…”