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The growing process of a spinel-like oxide film can be obtained through different atmospheres; in this sense Air, O 2 , steam, and nitrogen atmospheres were used in different steps during the aging heat treatment at 490ºC of maraging 300 and 350 alloys. The oxidation layer produced under different atmospheres was chemically, microstructurally and mechanically characterized by means of advanced techniques. The results showed (in both alloys) a non-homogeneous mix oxide formed by magnetite, nickel and cobalt ferrites and MoO 3 heterogeneously distributed along the oxide thickness. It was also founded TiO 2 in the innermost areas and a particularly important quantify of hematite on the external surface. A nickel-rich austenite phase was produced at the interphase due to the combination of nickel stability and the preference of cobalt, molybdenum, and iron diffuses through the film as ions. The highest thickness values were found in the oxides produced in maraging 300 steels which could indicate greater susceptibility to oxidation comparing with grade 350 maraging steel. The oxide films produced in both maraging alloys using air atmosphere presents excellent adherence, and the results show the capability for being used for tribological applications under sliding contact tests.

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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.

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Resumo O aço com alto manganês tem sido estudado como alternativa mais barata em substituição às ligas de aço mais utilizadas, devido as suas propriedades de resistência, ductilidade e tenacidade. Foi alterada a composição de manganês para teores acima dos teores dos aços Hadfield, visando sua aplicação em temperaturas criogênicas. Foram obtidas ligas de aço com alto teor de Manganês através do processo de fundição. O objetivo é avaliar as alterações provocadas pelo aumento do Manganês no aço fundido. Através do estudo realizado no Thermo-Calc®, as amostras da liga fundida foram submetidas à laminação a quente e posterior tratamento térmico de solubilização a 700 ºC, com o intuito de manter a microestrutura austenítica. As mesmas foram analisadas quanto à microestrutura por microscopia ótica (MO) e microscopia eletrônica de varredura (MEV). Os ensaios de dureza realizados confirmaram a elevada dureza das ligas, bem como a variação entre as ligas no estado fundido e solubilizado.

Thermo-mechanically controlled rolling is a technique used to produce steel strips and plates. One of the steels widely used in the production of heavy plates for application in oil and gas pipelines is API X80. The hot rolling process of this family of steels consists of applying deformation passes at high temperatures, mainly above Ae3, inside the austenite phase field. It has been shown that during deformation, the phenomenon of dynamic transformation (DT) of austenite into ferrite leads to lower hot deformation resistance within the stable austenite region. In this investigation, hot torsion simulations of an industrial rolling process under continuous cooling conditions were used to monitor the formation of ferrite by DT. Stress–strain flow curves and equivalent mean flow stresses followed by sample characterization via optical and electron microscopy showed the inevitable formation of ferrite above the Ae3. The employed 10-pass deformation schedule was divided into 5 roughing and 5 finishing passes, thereby promoting an increased volume fraction of ferrite and decreased critical strain for the onset of DT and dynamic recrystallization (DRX). A microstructural analysis confirmed the formation of ferrite from the first roughing strain until the last finishing pass. The volume fraction of DT ferrite increased due to strain accumulation, an increased number of deformation passes and as the temperature approached the Ae3, leading to a characteristic torsion texture at the end of the simulation.