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URI permanente para esta coleçãohttps://repositorio.fei.edu.br/handle/FEI/795
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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.- Electrochemical characterization of 13Cr low-carbon martensitic stainless steel - Corrosion study with a mini-cell setup(2022-10-27) CALDERON- HERNANDEZ, J. W.; GONZALEZ-RAMIREZ, M. F.; SEPULVEDA-CASTANO, J. M.; SANTOS-MARTINEZ, J. D.; QUISPE-AVILES, J. M.; Rodrigo Magnabosco; Goldenstein H.© 2022 The Authors.13Cr low-carbon martensitic stainless steels also known as supermartensitic stainless steels (SMSS) have superior properties than conventional martensitic stainless steels. The SMSS have better weldability and corrosion resistance. Nevertheless, corrosion resistance depends on phases transformations which are induced generally by heat treatments. In this work, the electrochemical properties of a SMSS were evaluated as a function of the tempering temperature (400 °C-700 °C). The susceptibility to intergranular corrosion was determined throught the degree of sensitization (DOS) using the Double Loop - Electrochemical Potentiokinetic Reactivation technique (DL-EPR) in a conventional three electrodes corrosion cell. On the other hand, the pitting susceptibility was evaluated by potentiodynamic polarization using a homemade corrosion mini-cell (based on a sessile electrolyte droplet), thus avoiding crevice problems typically seen with conventional arrangements. Imaging the microstructure with SEM, XRD analysis and thermodynamic and kinetic simulations were performed to understand the microstructural transformations and their relationship with corrosion resistance. The most severe sensitization occurs at the temperature where reversed austenite transformation is highest.
- Effect of aging heat treatment H950 and H1000 on mechanical and pitting corrosion properties of uns s46500 stainless steel(2018-01-05) BERALDO, C. H.; CALDERON-HERNANDEZ, J. W.; Rodrigo Magnabosco; ALONSO-FALLEIROS, N.© 2018 Universidade Federal de Sao Carlos. All rights reserved.The effect of aging temperature on mechanical and pitting corrosion properties of UNS S46500 was investigated. Tensile and Hardness tests were carried out and the microstructure was analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction; Thermo-Calc simulations helped in the phase identification. Pitting corrosion properties were investigated in 0.6M NaCl electrolyte with sulfate additions by Potentiodynamic Polarization (PP). Hardness, tensile and yield strength of the UNS S46500 steel after lower aging temperature, 510ºC (H950), are higher than the ones found in the 538ºC (H1000) aged steel.This result is explained by microstructure, X-ray diffraction and Thermo-Calc analysis, which indicated the presence of austenite, chi phase and probably Ni3Ti precipitates finely and uniform distributed throughout the martensite matrix. Pitting corrosion resistance is equivalent in both aging temperatures. The sulfate inhibitor effect on UNS S46500 steel was enhanced for 538ºC condition when the electrolyte reaches 1Cl-:1SO4 2- ratio, which is explained by Ni sulfate adsorption and the amount of interfaces in the microstructure resulting in smaller amount of adsorption sites, such as coarsened Ni3Ti precipitates, smaller fraction of chi phase and recovery of dislocations in martensite structure.
- Investigation of the effect of the interstitial content on the degree of sensitization at 600°C in ferritic stainless steels Investigação do efeito do teor de intersticiais sobre o grau de sensitização em aços inoxidáveis ferríticos a 600°C(2007-01-05) SERNA-GIRALDO, C. A.; IDE, C. R.; Rodrigo Magnabosco; KUNIOSHI, C. T.; ALONSO-FALLEIROS, N.The purpose of this work was to investigate the effect of carbon and nitrogen in 17%Cr ferritic stainless steels (16%Cr-0.04%C-0.032%N; 17.2%Cr-0.02%C-0.0062%N; 18.5%Cr-0.008%C-0.0213%N) on the degree of sensitization (DOS). These steels were solution annealed at 1200°C and quenched in water. Isothermal treatments were carried out at 600°C between 5 minutes and 16 hours. The Double Loop Electrochemical Potentiokinetic Reactivation test (DL-EPR) was carried out in a 0.5M H2SO4 solution at (25 ± 2)°C. The DOS was evaluated using a ratio between maximum anodic current density in reversion, ir and activation, ia. The microstructural examination of specimens was carried out using optical and scanning electron microscopy after metallographic etching with Vilella's reagent. The results showed a DOS variation with time. Maximum values of DOS were obtained for each steel, followed by its reduction. The intensity of DOS and its kinetics vary in function of the carbon and nitrogen content in steels.
- Corrosion versus mechanical tests for indirect detection of alpha prime phase in UNS S32520 super duplex stainless steel(2011-04-05) FONTE, T. F.; Rodrigo Magnabosco; TERADA, M.; PADILHA, A. M.; COSTA, I.Alpha prime formation leads to material embrittlement and deterioration of corrosion resistance. In the present study, the mechanical and corrosion behavior of super duplex stainless steel UNS S32520 aged at 475°C from 0.5 h to 1,032 h was evaluated using microhardness measurements, Charpy impact tests, electrochemical impedance spectroscopy, and cyclic polarization curves. The sensibility of these tests to the effects of alpha prime phase was investigated. The microhardness test showed a gradual increase in hardness with aging time, whereas the impact tests revealed losses of about 80% in the energy absorption capacity for the material aged for 12 hin comparison with the solution-annealed samples. The most responsive analysis was the impact test, which indirectly revealed the presence of this deleterious phase in samples aged for 0.5 h. The electrochemical impedance spectroscopy and polarization tests were not highly sensitive to the alpha prime phase unless these are present In large amounts in the stainless steel. © 2011, NACE International.
- Comparison between stainless steels and Nickel alloys through pitting corrosion resistance electrochemical tests(2021-04-27) FRAZÃO, I.; Rodrigo Magnabosco; DELBLANC, A.© 2021 Universidade Federal de Sao Carlos. All rights reserved.Critical pitting temperature (CPT) is one of the most accepted criteria for alloy classification concerning pitting corrosion. The techniques used nowadays to determine CPT have different parameters for alloys of different material classes, preventing the comparison between stainless steels and nickel based alloys. This study aims to compare the corrosion resistance of nickel based alloys and stainless steels with high corrosion resistance through potentiostatic tests for CPT determination, using a 3M MgCl2 aqueous solution. CPT values were effectively determined for the stainless steels studied but the technique did not have the same efficiency for nickel based alloys due to the occurrence of crevice corrosion, even considering the higher PRE of nickel based alloys.
Artigo Relation Between Pitting Potential and PREN Values for Ferrite and Austenite in Duplex Stainless Steels(2019-12-12) SANTOS, D.C; MACARRAO, I. M.; Rodrigo MagnaboscoThis work aims to investigate the relation between PREN of ferrite and austenite and the pitting potential of UNS S31803 DSS. Samples were solution-treated between 1040 °C and 1150 °C generating different phase fractions and, consequently, different alloy element contents. ThermoCalc® thermodynamic simulations were performed to predict the chemical composition of each phase allowing the PREN calculations. Besides, potentiodynamic polarization tests were conducted in 0.6 M NaCl solution at 70 °C to correlate pitting potential (Epit) and PREN. Thermodynamic simulation reveals that PREN for ferrite is higher than austenite between 975 °C and 1300 °C. Nevertheless, the electrochemical results show a slight reduction of pitting potential with increasing ferrite content, probably related to the reduction of Cr and Mo contents in this phase. Pits were found preferably in ferrite and in ferrite/austenite interfaces. This behavior suggests that, even with only a slight reduction of pitting potential and, consequently, a discrete corrosion resistance reduction, ferrite is more susceptible to pitting. No pits were found in austenite, suggesting that higher N contents are fundamental to maintain the corrosion resistance of this phase.- Formation of Cu-rich Nanoprecipitates in Cu Containing Pearlitic SGI(2020-11-29) GARCÍA, LAURA N.; Rodrigo Magnabosco; BOERI, ROBERTO E.; TOLLEY, ALFREDO J.; SAAVEDRA, MARCELA E.The presence of Cu-rich nanoprecipitates in a pearlitic spheroidal graphite (ductile) cast iron alloyed with 0.82 wt%Cu was studied. The size and distribution of the precipitates were examined by transmission electron microscopy at different locations of the pearlitic matrix. Some areas were nearly free from precipitates, while other regions showed precipitates at the cementite and ferrite lamellae and at the ferrite/cementite interface. Calculation of the thermodynamic equilibrium under stable and metastable conditions using Thermo-Calc led to the identification of the conditions controlling the formation of Cu-rich nanoprecipitates along three different stages depending on the Cu concentration. Together with a differential scanning calorimetry test and elemental diffusional calculations, thermodynamic predictions supported the observation of Cu-rich precipitates despite the low concentration of Cu of the alloy investigated and allowed the authors to explain the observed heterogeneity in the distribution of precipitates as resulting from the heterogeneous distribution of Cu in the alloy caused by microsegregation during solidification. The knowledge gained is relevant for the design of strengthening strategies in SGI based on the dispersion of Cu-rich nanoprecipitates.
- Use of DICTRA® simulations to support carbide particle growth study in NbC-Ni cemented carbide(2020-07-24) MORAIS, LUARA DA COSTA; BENEDUCE, FLAVIO; Rodrigo Magnabosco; RIBEIRO, TIAGO RAMOSCarbide particle growth observed in a NbC-12%Ni (mass percent) sample sintered at 1420 °C was discussed using DICTRA® simulation of spherical particles immersed in a Ni matrix. It is possible to describe the liquid formation during sintering using a model that assumes a spherical region of NbC, with radius equivalent to the NbC particle distribution, surrounded by nickel. NbC volume fraction was obtained for different simulation times allowing the evaluation of the dissolution behavior in different particle sizes. Small carbides (around 1 μm in diameter) suffered total dissolution, while major carbides (10 μm in diameter) did not dissolve during the simulation. Chemical content evidenced that Nb and C from carbide dissolution segregated to liquid phase reaching levels up to 15 and 2%, respectively, showing the availability of this elements to re-precipitate in non-dissolved carbides during cooling from sintering temperature. The simulations indicate that carbide particle growth observed in NbC-12%Ni sintered sample can be a result of dissolution and re-precipitation mechanism.
- Effect of MAG welding transfer mode on sigma phase precipitation and corrosion performance of 316L stainless steel multi-pass welds(2020-08-07) GUILHERME, L. H.; BENEDETTI, A. V.; FUGIVARA, C. S.; Rodrigo Magnabosco; OLIVEIRA, M. F.The effect of multi-pass MAG welding transfer modes on the sigma phase precipitationand corrosion performance of AISI 316L thick plate were investigated. The evolution of themicrostructure was examined by optical and electron microscopy as well as ferritscope mea-surements and energy dispersive X-ray spectrometry. An electrochemical microcell was thenused to characterize the electrochemical behaviour of the different weld regions. The fusionline was the most critical zone for pitting corrosion for all welding procedures, due to thesigma phase precipitation, alloy elements partitioning and galvanic coupling between basemetal and weld metal. It was observed the formation of sigma phase after short-circuitingor spray-arc modes, with no evidence of it to the pulsed-arc, which obtained the best cor-rosion resistance performance. The results evidenced the selective corrosion around sigmaphase due to the depletion in Cr and Mo, with subsequent pitting nucleation. A strongcorrelation between the MAG welding transfer modes and the sigma phase morphologywas observed. The influence of weld parameters on microstructure evolution and corrosionresistance performance was discussed. The corrosion resistance performance of the MAGwelding procedures was ranked as: pulsed-arc > short-circuit > spray-arc.