Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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15 resultados
Resultados da Pesquisa
Artigo de evento 1 Citação(ões) na Scopus Pit morphology and its microstructure relation in 850°C aged UNS S31803 (SAP 2205) duplex stainless steel(2003-07-24) Rodrigo Magnabosco; ALONSO-FALLEIROS, N.This work described the relationship between microstructure of UNS S 31803 (SAP 2205) aged at 850°C and pitting morphology after cyclic polarization in chloride aqueous solution. The initial material, solution treated for 30 minutes at 1120°C and water quenched, was aged at 850°C for periods up to 100 hours. Cyclic polarization in 3,5% NaCl aqueous solution was conducted on #600 grounded sample surfaces. After polarization, the samples were sectioned transversal and perpendicular to polarized surface to allow the inner view of pitting corrosion using scanning electron microscope. It was found that sigma phase formation after 850°C aging treatment reduced pitting potential, and pitting corrosion occurred as selective corrosion of chromium and molybdenum impoverished regions, like interfaces between sigma phase and metallic matrix.Artigo de evento 0 Citação(ões) na Scopus UNS S31803 stainless steel phase transformations during 475°C and 650°C aging and its influence on the pitting potencial in a 0.6M NaCl solution(2010-07-26) MELO, E. B. DE; Rodrigo MagnaboscoThis work evaluates the phase transformations during aging at 475°C or 650°C of UNS S31803 duplex stainless steel and its influence on the pitting potential in a 0.6M NaCl solution. The material was solution treated at 1175°C and water quenched, and then aged at 475°C or 650°C for times up to 360h. Samples were a nalyzed by optical microscopy through quantitative metallography, and ferrite quantification was conducted with a ferritscope. Vickers microhardness measurements were also performed. Cyclic polarization tests were then conducted in a 0.6M NaCl solution, at a scan rate of 1 mV/s. It is found that aging at 475°C leads to a continuous increasing of material microhardness, probably related to the presence of alpha prime phase, and reduction in the pitting potentials were observed for samples aged for more than 12 h. Samples aged at 650°C show the presence of sigma and chi phases, which increased with aging time, and pitting potential is reduced for aging times greater than 4h. The pitting potential reduction in the aged samples is probably associated with the presence of ferrite and/or austenite impoverished in Cr and Mo, as a result of alpha prime formation at 475°C or sigma and chi formation at 650°C.Artigo de evento 0 Citação(ões) na Scopus Influenzce of the sigma phase formation in pitting potential of UNS s31803 duplex stainless steel in 0,6M NACL AGED at 850 E 900°C(2010-07-26) Daniella Caluscio dos Santos; Rodrigo MagnaboscoThe main purpose of this work is to analyze the mechanisms and kinetics of sigma phase formation of UNS S31803 stainless steel after isothermal aging between 850 e 900°C, evaluating the influence of sigma phase formation on pitting potential in 0.6M NaCl solution. Solution treated samples of the UNS S31803 duplex stainless steel were isotermically aged at 850°C or 900°C up to 360 h. The microstructural characterization of the samples was made through quantitative metallography, ferritscope analysis and Vickers microhardness. The cyclic polarization tests used to the determination of the pitting potential were conducted in polished samples. The electrochemical behavior of aged UNS S31803 duplex stainless steel in 0.6M NaCl solution is strongly dependent on the microstructure, since both changes in mechanisms and kinetics of sigma phase formation influenced the pitting potential of the material. Increasing aging time lead to the decrease of pitting potential, due to the formation of chromium impoverished regions. Oscillations in pitting potential values were noted due to the chromium redistribution enabled by easy diffusion of this element in high temperatures.Artigo de evento 0 Citação(ões) na Scopus Ferrite-to-austenite transformation during cold working of a duplex stainless steel(2011-09-23) Rodrigo Magnabosco; TAVARES, D. B.; FORGAS, A.; DE MOURA NETO, C.Ferrite-austenite duplex stainless steels (DSS) are replacing austenitic stainless steels in many applications due to its high mechanical and corrosion resistance. However, magnetic measurements of ferrite volume fraction using a ferritscope of cold worked samples indicate a reduction in the ferrite content with increasing mechanical work. Considering this fact, this work studies the influence of the cold working on the ferrite/austenite ratio. Samples of UNS S31803 DSS sheet, originally 3 mm thick, were solution-treated at 1175°C for 30 minutes and water quenched; after that, different levels of cold working were applied. Ferrite volume fraction was determined using two distinct methods: quantitative stereology with an optical microscope and magnetic measurements using a ferritscope; a detailed microstructural characterization, including X-ray diffractometry, was conducted to base the discussion of a possible ferrite-to-austenite diffusionless transformation.Artigo de evento 3 Citação(ões) na Scopus Comparative study of ferrite quantification methods applied to duplex stainless steels(2011-09-23) Rodrigo Magnabosco; SPOMBERG, S.Duplex stainless steels (DSS) present approximately the same quantities of ferrite (magnetic phase) and austenite. These steels are replacing austenitic stainless steels in some applications due to its high mechanical and corrosion resistance. However, changes in the volumetric percentage of those phases can modify material properties, justifying the development of this study, which has as principal aim a comparison between three different ferrite quantification methods. Samples of two different DSS (UNS S31803 or UNS S32750), originally supplied as 20mm round bars, were solution-treated between 1000°C and 1250°C, in order to obtain different ferrite/austenite ratios. Ferrite quantification was performed in three sections: longitudinal, transverse and diagonally oriented to the rolling direction. The volume fraction of ferrite was determined using three distinct methods: quantitative stereology with an optical microscope, magnetic measurements using a ferritscope, and X-ray analysis by comparison of the relative intensities of peaks corresponding to the planes that generate maximum intensity of diffraction for single-phase samples. Results are discussed, analysing the reliability of the studied methods.- Kinetic Study to Predict Sigma Phase Formation in Duplex Stainless Steels(2016) dos Santos D.C.; Magnabosco R.© 2016, The Minerals, Metals & Materials Society and ASM International.This work presents an improved kinetic study of sigma phase formation during isothermal aging between 973 K and 1223 K (700 °C and 950 °C), based on Kolmogorov-Johnson-Mehl-Avrami (K-J-M-A) model, established from volume fraction of sigma phase determined in backscattered electron images over polished surfaces of aged samples. The kinetic study shows a change in the main mechanism of sigma formation between 973 K and 1173 K (700 °C and 900 °C), from a nucleation-governed stage to a diffusion-controlled growth-coarsening stage, confirmed by a double inclination in K-J-M-A plots and microstructural observations. A single inclination in K-J-M-A plots was observed for the 1223 K (950 °C) aging temperature, showing that kinetic behavior in this temperature is only related to diffusion-controlled growth of sigma phase. The estimated activation energies for the nucleation of sigma phase are close to the molybdenum diffusion in ferrite, probably the controlling mechanism of sigma phase nucleation. The proposed time-temperature-transformation (TTT) diagram shows a “double c curve” configuration, probably associated to the presence of chi-phase formed between 973 K and 1073 K (700 °C and 800 °C), which acts as heterogeneous nuclei for sigma phase formation in low aging temperatures.
- Influence of the Heterogeneous Nucleation Sites on the Kinetics of Intermetallic Phase Formation in Aged Duplex Stainless Steel(2017) Melo E.A.; Magnabosco R.© 2017, The Minerals, Metals & Materials Society and ASM International.The aim of this work is to study the influence of the heterogeneous nucleation site quantity, observed in different ferrite and austenite grain size samples, on the phase transformations that result in intermetallic phases in a UNS S31803 duplex stainless steel (DSS). Solution treatment was conducted for 1, 24, 96, or 192 hours at 1373 K (1100 °C) to obtain different ferrite and austenite grain sizes. After solution treatment, isothermal aging treatments for 5, 8, 10, 20, 30, or 60 minutes at 1123 K (850 °C) were performed to verify the influence of different amounts of heterogeneous nucleation sites in the kinetics of intermetallic phase formation. The sample solution treated for 1 hour, with the highest surface area between matrix phases, was the one that presented, after 60 minutes at 1123 K (850 °C), the smaller volume fraction of ferrite (indicative of greater intermetallic phase formation), higher volume of sigma (that was present in coral-like and compact morphologies), and chi phase. It was not possible to identify which was the first nucleated phase, sigma or chi. It was also observed that the phase formation kinetics is higher for the sample solution treated for 1 hour. It was evidenced that, from a certain moment on, the chi phase begins to be consumed due to the sigma phase formation, and the austenite/ferrite interface presents higher SV for all solution treatment times. It was also observed that intermetallic phases form preferably in austenite-ferrite interfaces, although the higher occupation rate occurs at triple junction ferrite-ferrite-ferrite. It was verified that there was no saturation of nucleation sites in any interface type nor triple junction, and the equilibrium after 1 hour of aging at 1123 K (850 °C) was not achieved. It was then concluded that sigma phase formation is possibly controlled by diffusional processes, without saturation of nucleation sites.
- Use of composition profiles near sigma phase for assessment of localized corrosion resistance in a duplex stainless steel(2019) Magnabosco R.; da Costa Morais L.; dos Santos D.C.© 2018 Elsevier LtdPitting corrosion potential of a UNS S31803 duplex stainless steel (DSS) heat treated between 750 °C and 850 °C at different aging times was related to the extent of the Cr- and Mo-depleted areas at sigma-ferrite and sigma-austenite interfaces, estimated using DICTRA® simulations. It is possible to describe the sigma formation kinetics using a model that assumes a spherical region of austenite, with radius equivalent to the mean intercept of austenite islands, surrounded by ferrite. Composition profiles at sigma-ferrite and sigma-austenite interfaces were calculated, allowing the evaluation of the degree of depletion in Cr and Mo at sigma interfaces. There is a reduction of pitting potential with increase of the degree of depletion, characterized as the weighted sum of depleted areas in Cr and Mo composition profiles, making possible the assessment of the localized corrosion resistance of aged DSS through simulation of sigma phase formation.
- Evaluation of microstructural effects on the degree of sensitization (DOS) of a UNS S31803 duplex stainless steel aged at 475°C(2015) De Melo E.B.; Magnabosco R.© 2015, NACE International.In this study, microstructural and electrochemical behavior of a UNS S31803 duplex stainless steel aged at 475°C were investigated. Hardness values increased with aging at 475°C and evidence of alpha prime (α′) phase formation was confirmed by transmission electron microscopy analysis. Double loop electrochemical potentiokinetic reactivation measurements in a 2 M H2SO4 + 0.5 M NaCl + 0.01 M KSCN solution showed an increase in the degree of sensitization values, mainly for the sample aged for 360 h at 475°C. Moreover, the results suggest that α′ phase formation occurred via spinodal decomposition mechanism.
- Experimental investigations and DICTRA® simulation of sigma phase formation in a duplex stainless steel(2017) Morais L.D.C.; Magnabosco R.© 2017 Elsevier LtdSigma phase formation in an UNS S31803 duplex stainless steel aged at 940 °C was evaluated by computational simulation in DICTRA® software, using MOB2 diffusion database and TCFE8 thermodynamic database. Simulation results were compared to experimental tests. Two models were tested in DICTRA® software: in model 1 sigma phase are placed between ferrite and austenite, and in model 2 sigma is placed at one side of ferrite region, and austenite on the other. The volume fraction of sigma and ferrite phases obtained in model 1 showed adherence to the experimental results up to 7200 s (2 h) of simulation, indicating the ability of the model in the description of early stages of sigma formation. Model 2 showed good agreement with experimental data up to 86,400 s (24 h) of simulation. The composition profile obtained by the simulation of the model 1 represented better the impoverishment in Cr and Mo in ferrite/sigma and austenite/sigma interfaces, while the profiles obtained by the simulation of model 2 described better the partition of the chemical elements between austenite and ferrite during sigma formation.