Neusa Alonso-Falleiros

Correlation between Corrosion Potential and Pitting Potential for AISI 304L Austenitic Stainless Steel in 3.5% NaCl Aqueous Solution

We investigated the effect of surface finish of two AISI 304L (UNS S30403) stainless steels on the corrosion potential (Ecorr) in 3.5% NaCl aqueous solution and its value was compared with the pitting potential (Ep) value and the type of anodic potentiodynamic curve obtained for determination of Ep in this solution. Five different surface finishes were examined. Ecorr and its standard deviation are strongly affected by the type of surface finish. Moreover, there are evidences of a linear correlation between Ecorr and Ep, as well as between the percentage of anodic curves with a well-defined pitting potential and the uncertainty in the determination of Ecorr.

Effect of niobium on corrosion resistance to sulfuric acid of 430 ferritic stainless steel

The influence of niobium on corrosion resistance to 0.5M H2SO4 of 17% Cr ferritic stainless steels, to which it was added in amounts larger than that necessary to stabilize the interstitial elements, was investigated. Their performance was compared to that of other two Fe-17%Cr alloys, one without additions and another containing 0.93% molybdenum. Through weight and electrochemical measurements and through morphologic examination of corroded surface it was found that the corrosion of these alloys, with the exception of that containing molybdenum, proceeds in two different steps. In the first step (up to about 60 min) the corrosion rate practically does not change with time, the lower rates being displayed by alloys containing larger amounts of Nb. In the second stage the corrosion rate increases with time. The corrosion rate of Mo containing alloy is constant for all times.

Selective Corrosion in Sodium Chloride Aqueous Solution of Cupronickel Alloys with Aluminum and Iron Additions

Abstract 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 densitie...

Investigação do efeito do teor de intersticiais sobre o grau de sensitização em aços inoxidáveis ferríticos a 600ºC

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 Vilellas 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.

ESTUDIO DE LA RESISTENCIA A LA CORROSIÓN DE ACEROS INOXIDABLES AUSTENITICOS USADOS EN IMPLANTES QUIRURGICOS

In this work, both pitting corrosion resistance and intergranular corrosion resistance were evaluated for three austenitic stainless steels, used in implants. The resistance to pitting corrosion was evaluated through electrochemical tests. By using Practice A (ASTM A262) and the electrochemical potentiodynamic reactivation tests, intergranular corrosion was analyzed. The P558 steel presented greater resistance to pitting corrosion than the F1586 and F138 steels. When solubilized the steels showed high resistance to intergranular corrosion, and cero sensitization degree. After thermal treatment only the P558 steel was sensitized.