Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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5 resultados
Resultados da Pesquisa
- 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.
- 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.
- 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.