Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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8 resultados
Resultados da Pesquisa
- Relation between pitting potential, degree of sensitization, and reversed austenite in a supermartensitic stainless steel(2017) Calderon-Hernandez J.W.; Hincapie-Ladino D.; Filho E.B.M.; Magnabosco R.; Alonso-Falleiros N.© 2017, NACE InternationalPitting potential (Ep) and degree of sensitization (DOS) of a supermartensitic stainless steel (SMSS) were determined on specimens heat-treated at different tempering temperatures (550°C, 575°C, 600°C, 625°C, 650°C, or 700°C). The effect of pH (pH 6 and pH 8) on the Ep obtained in a 3.5 wt% NaCl solution, as well as the correlation between Ep and DOS obtained in 0.5 M H2SO4 + 0.01 M KSCN solution, was studied. The results showed correlation between Ep and DOS values, the samples with the higher DOS values being the ones with the lower Ep. A mechanism was proposed that would explain the correlation of the presence of reversed austenite formed during tempering, Ep, and DOS.
- 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.
- Effect of Mo substitution by W on the passive characteristics and mechanical properties of AISI 316L austenitic stainless steel(2019) Terra B.C.M.; Magnabosco R.© 2019 NACE International.This work studied the influence on pitting corrosion resistance and mechanical behavior of the partial or total substitution of Mo by W in AISI 316L austenitic stainless steel. Alloys that contain 0%, 25%, 50%, 75%, or 100% of Mo substitution by W in atomic content were produced and analyzed. Microstructural analysis showed that W does not cause any difference in the size, distribution, and composition of inclusions. However, the grain sizes are slightly reduced in samples with W. Tensile tests did not show any difference in their mechanical properties. Cyclic polarization results do not show any difference between the samples with and without W in 3.5% NaCl at room temperature. However, the sample with 50% W and 50% Mo showed the highest critical pitting temperature in 1 M NaCl solution after potentiostatic polarization at 180 mVAg/AgCl, 40±4°C. This result shows a synergic effect of Mo and W for pitting corrosion resistance of austenitic stainless steel.
- Influence of sigma phase formation on pitting corrosion of an aged uns s31803 duplex stainless steel(2013) Dos Santos D.C.; Magnabosco R.; De Moura-Neto C.The main purpose of this contribution was the study of the relation between sigma formation and pitting corrosion resistance of a UNS S31803 duplex stainless steel aged at 850°C. Solution-treated samples were isothermally aged at 850°C for up to 360 h. The corrosion resistance of aged UNS S31803 steel was analyzed through cyclic potentiodynamic polarization tests in 0.6 M sodium chloride (NaCl) solution. The main mechanism of sigma phase formation was nucleation and growth from ferrite, in agreement to the Johnson-Mehl-Avrami- Kolmogorov kinetics model. This model suggests a change on the mechanisms of sigma phase formation from nucleation and growth from ferrite to the growth from austenite. Pitting morphology was related to the material microstructure. The pitting growth mechanism occurred by selective corrosion of the chromium-depleted areas of the specimens. Both pitting and repassivation potentials decreased with an increase of sigma volume fraction. Recovery of the corrosion resistance was observed in the early stages of sigma formation, probably related to chromium redistribution to depleted areas. © 2013, NACE International.
- Sensitization and pitting corrosion resistance of ferritic stainless steel aged at 800°C(2006) Paroni A.S.M.; Alonso-Falleiros N.; Magnabosco R.This work investigates the influence of sensitization conditions on pitting corrosion resistance of ferritic stainless steel UNS S43000 aged at 800°C between 10 min and 320 min. UNS S43000 steel is susceptible to intergranular corrosion after solution treatment at 1,160°C followed by water-quenching, as a consequence of the chromium depletion of the grain boundaries adjacent areas, due to chromium carbide precipitation during cooling. Isothermal treatments of 10 min at 800°C decrease the sensitization degree, and intergranular corrosion resistance is recovered after 20 min at 800°C. The solution-treated specimens have a high pitting potential in 3.5% sodium chloride (NaCl) solution compared to the same material treated at 800°C for 10 min. The resistance to pitting corrosion is reduced by chromium depletion associated with an increase of inter- and intragranular precipitation of chromium carbide. For treatments longer than 20 min at 800°C, the pitting corrosion resistance returns to the high level observed for the solution-treated condition, as a consequence of chromium redistribution that occurs after 20 min at 800°C. The scan rate used in potentiodynamic tests plays a minor role on the pitting potential, while a rougher surface leads to lower pitting potentials in all studied conditions. © 2006, NACE International.
- Pit morphology and its relation to microstructure of 850°C aged duplex stainless steel(2005) Magnabosco R.; Alonso-Falleiros N.The relation between pit morphology and microstructure formed during 850°C isothermal aging of UNS S31803 duplex stainless steel (DSS) could be reached through the explanation of pit nucleation and growth during potentiodynamic polarization in 3.5 wt% sodium chloride (NaCl) aqueous solution. Aging times up to 10 min at 850°C led to sigma formation by direct precipitation from ferrite, resulting in Cr- and Mo-depleted ferrite, or secondary ferrite. Between 30 min and 5 h of aging, the ferrite suffered eutectoid decomposition, resulting in sigma phase and secondary austenite, also impoverished in Cr and Mo. Those Cr- and Mo-depleted zones around the sigma phase were preferential sites for the nucleation of pits. At those sites, the passive film breakdown was easier, as shown by the low pitting potential values found in aged samples. Pit growth occurred as selective corrosion of the metallic matrix surrounding the sigma phase, as a consequence of the lower corrosion resistance of the secondary ferrite and austenite phases found. The low passivation potential values indicated the difficulty in repassivation of the pits formed, probably related to the Cr and Mo depletion of the regions surrounding the sigma phase. © 2005, NACE International.
- Selective corrosion in sodium chloride aqueous solution of cupronickel alloys with aluminum and iron additions(2007) Liberto R.C.N.; Magnabosco R.; Alonso-Falleiros N.Cupronickel pipes are widely used in cooling systems. Under this application, localized corrosion is observed, particularly associated with selective corrosion of nickel (denickelification). This work studied the denickelification process in solution-treated cupronickel alloys 90-10 (Cu-10wt%Ni), with aluminum and iron additions, in 0.01 M, 0.1 M, or 0.6 M sodium chloride (NaCl) aqueous solutions. Polished surfaces of the studied materials were submitted to potentiodynamic polarization, and after that, the polarized surfaces were studied using optical microscopy (OM) and scanning electron microscopy (SEM) assisted by energy-dispersive spectroscopy (EDS). A passivity break potential (Epb) was determined in all solutions, related to the initiation of selective corrosion of nickel. When submitted to cyclic potentiodynamic polarization, alloys with higher Epb showed the higher nickel losses in localized spots. However, potentiodynamic polarization tests conducted in 0.01 M NaCl until current densities of 10-1 A/cm2 were reached showed that the selective corrosion process was stopped by the formation of copper-rich corrosion products over the surface. © 2007, NACE International.
- Sigma phase formation and polarization response of UNS S31803 in sulfuric acid(2005) Magnabosco R.; Alonso-Falleiros N.For a better understanding of the relationship between the microstructure of UNS S31803 duplex stainless steel (DSS) and the shape of the polarization curves, this study evaluated the influence of the microstructure on the potentiodynamic polarization of the 850°C isothermal-aged UNS S31803 DSS in 0.5 M sulfuric acid (H2SO4). In the transpassive region, selective corrosion of chromium- and molybdenum-rich phases occurred. In the solution-treated sample, ferrite was selectively corroded, and in all aged samples, the sigma phase was the selectively corroded phase. Five current density maxima in the passive region were found during potentiodynamic polarization, and they can be related to the microstructures formed. The current density maximum at 564 mV us. saturated calomel electrode (SCE) can be related to secondary ferrite, impoverished in chromium and molybdenum, that was formed during direct precipitation of sigma phase from the original ferrite. Secondary austenite, impoverished in chromium and molybdenum and formed together with the sigma phase during eutectoid decomposition of the original ferrite, can be related to the current density maxima at -85 mVSCE and -40 mVSCE. The austenite phase, present in all heat-treatment conditions, can be related to the current density maxima at -155 mVSCE and 111 mVSCE. © 2005, NACE International.