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Physical simulation is a useful tool for examining the events that occur during the multiple stages of thermomechanical processing, since it requires no industrial equipment. Instead, it involves hot deformation testing in the laboratory, similar to industrial-scale processes, such as controlled hot rolling and forging, but under different conditions of friction and heat transfer. Our purpose in this work was to develop an artificial neural network (ANN) to optimize the thermomechanical behavior of stainless-steel biomaterial in a double-pass hot compression test, adapted to the Arrhenius–Avrami constitutive model. The method consists of calculating the static softening fraction (Xs) and mean recrystallized grain size (ds), implementing an ANN based on data obtained from hot compression tests, using a vacuum chamber in a DIL 805A/D quenching dilatometer at temperatures of 1000, 1050, 1100 and 1200 °C, in passes (ε1 = ε2) of 0.15 and 0.30, a strain rate of 1.0 s−1 and time between passes (tp) of 1, 10, 100, 400, 800 and 1000 s. The constitutive analysis and the experimental and ANN-simulated results were in good agreement, indicating that ASTM F-1586 austenitic stainless steel used as a biomaterial undergoes up to Xs = 40% of softening due solely to static recovery (SRV) in less than 1.0 s interval between passes (tp), followed by metadynamic recrystallization (MDRX) at strains greater than 0.30. At T > 1050 °C, the behavior of the softening curves Xs vs. tp showed the formation of plateaus for long times between passes (tp), delaying the softening kinetics and modifying the profile of the curves produced by the moderate stacking fault energy, γsfe = 69 mJ/m2 and the strain-induced interaction between recrystallization and precipitation (Z-phase). Thus, the use of this ANN allows one to optimize the ideal thermomechanical parameters for distribution and refinement of grains with better mechanical properties. [ABSTRACT FROM AUTHOR]

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 (dDRX), steady-state stress (σss) 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. [ABSTRACT FROM AUTHOR]

The occurrence of dynamic transformation is investigated during the simulated hot rolling of an API‐X80 steel. Torsion tests are carried out under continuous cooling conditions, with all deformation passes applied above the equilibrium transformation temperature. Three different interpass times are investigated: 1, 8, and 20 s. Samples are water‐quenched before and after the odd‐numbered passes, and the volume fraction of ferrite is evaluated metallographically. Dynamic transformation took place under all conditions and the volume fraction of retained ferrite increased with the retained strain. The increase in flow stress during simulated rolling is less than expected under all conditions, which is evidence for the dynamic formation of ferrite. The driving forces and energies barriers are evaluated, indicating that dynamic transformation is mechanically activated. [ABSTRACT FROM AUTHOR]

A five-pass torsion simulation of the roughing passes applied during hot plate rolling was performed in the single-phase austenite region of a Nb-microalloyed steel under continuous cooling conditions. The deformation temperatures were approximately half-way between the Ae3 and the delta ferrite formation temperature (i.e., 250 °C above the Ae3) in which the free energy difference of austenite and ferrite is at maximum. The microstructures in-between passes were analyzed to characterize and quantify the occurrence of deformation-induced dynamic phase transformation. It was observed that about 7% of austenite transforms into ferrite right after the final pass. The results are consistent with the calculated critical strains and driving forces which indicate that dynamic transformation (DT) can take place at any temperature above the Ae3. This mechanism occurs even with the presence of high Nb in the material, which is known to retard and hinder the occurrence of DT by means of pinning and solute drag effects. The calculated cooling rate during quenching and the time–temperature–transformation curves of the present material further verified the existence of dynamically transformed ferrite. [ABSTRACT FROM AUTHOR]