Cheng Man

The Electrochemical Behavior and Characteristics of Passive Film on 2205 Duplex Stainless Steel Under Various Hydrogen Charging Conditions

The electrochemical behavior and the characteristic of 2205 duplex stainless steel (UNS S32205) under various hydrogen charging conditions in borate buffer solution containing chloride ion were evaluated by potentiodynamic measurements, electrochemical impedance spectroscopy, capacitance measurements (Mott-Schottky approach), and anodic polarization experiments. The results indicate that the hydrogen generated by the cathodic charging process decreased the corrosion resistance of 2205 duplex stainless steel, especially the pitting resistance of passive film. As a result of the hydrogen charging, the semiconductor characteristic of the passive film changed from n-type and p-type coexisting to only n-type existing, and the pitting susceptibility increased. Along with the charging process, the critical concentration of chloride for breakdown of passive film decreased and the repassivation process was prevented by hydrogen.

Effect of chloride concentration on passive film properties on copper

ABSTRACT The semiconducting properties of passive films formed on copper, in anaerobic alkaline sodium chloride solution, were studied using Mott–Schottky analysis and electrochemical impedance spectroscopy, based on the point defect model. Results showed that the corrosion resistance increased with increasing potential, which was attributed to a well crystallised, refined grain structure, and a thicker passive film at higher potential. P-type semiconducting characteristics were obtained with or without chloride. The density of copper vacancies was approximately 1020 cm−3, and increased with the increasing chloride concentration, which was attributed to faster film-formation in a higher chloride environment. The diffusion coefficient of the defects, a key dynamic parameter for passive film breakdown, was in the range of 10−16–10−15 cm2 s−1, and increased with increasing chloride concentration, thus leading to a greater probability of pitting.

The Combined Effect of Chemical and Structural Factors on Pitting Corrosion Induced by MnS-(Cr, Mn, Al)O Duplex Inclusions

In situ atomic force microscopy, scanning Kelvin probe force microscopy, and potential pulse technology were used to study the pitting behavior induced by inclusions in AM355 martensitic stainless ...

Characterization of the Passive Film and Corrosion of Martensitic AM355 Stainless Steel

ABSTRACT Electrochemistry methods were used to investigate the influence of pH on the passive film and corrosion behavior of ultrahigh strength AM355 stainless steel in chloride-containing media. Analysis of the Pourbaix diagram indicates that AM355 stainless steel exhibits higher corrosion resistance in natural and near-natural environments than that in acidic and alkaline conditions. Electrochemistry measurements and composition analysis of the passive film show that pitting potential increased due to the enhanced repassivation capacity of AM355 stainless steel with increasing pH. The mixed MnS/oxide inclusions are the main pitting sensitive locations under all conditions. Morphological observations and energy-dispersive spectroscopy showed that the influence of the gap between the martensitic laths is significant with increasing pH. The inclusions, element concentrations, and microstructures weaken the resistance of ultrahigh-strength martensitic AM355 stainless steel against corrosion.

The Correlation Between the Distribution/Size of Carbides and Electrochemical Behavior of 17Cr-1Ni Ferritic-Martensitic Stainless Steel

The correlation between the distribution/size of carbides and corrosion resistance of 17Cr-1Ni ferritic-martensitic stainless steel after different heat treatment temperatures was investigated by transmission electron microscope, electrochemical tests, and corrosion morphology observations. The results showed that the size of the precipitated phase decreased and corrosion resistance increased with an increase in the annealing temperature. When the tempering temperature was low (290 °C), carbides precipitated mainly at the phase boundaries due to a low degree of atomic matching and higher grain boundary energy. In this case, the polarization curve had a passivation interval and the pits were mainly initiated at the phase boundary. When the tempering temperature was higher than 400 °C, the carbides gradually precipitated in the martensite laths because the accelerated diffusion of Cr healed the Cr depletion zone at phase boundary. This outcome resulted in a polarization curve that had no passivation range and uniform corrosion occurred in martensitic region.

Characterization of the Outer Layer Nanostructure in the Electrochemical Response of Stainless Steel in Aqueous Sodium Hydroxide

ABSTRACT The outer layer nanostructure of stainless steel’s passive film in 0.1 M NaOH has been studied by electrochemical atomic force microscopy and the role of the outer layer in the electrochemical response of stainless steel has been characterized. The outer layer is mainly composed of nanoscale particles whose average diameter is up to 13.14 ± 3.52 nm at the end of the formation period. The formation process is characterized by the nucleation, growth, and contact of oxide particles. Based on the study on the outer layer nanostructure, the gaps/boundaries between particles in the outer layer should be diffusion paths for ions across the layer. The electrochemical impedance spectroscopy analysis revealed that the ion diffusion resistance first increased and then remained stable due to the three-dimensional growth of nanoscale particles.

Influence of oxide scales on the corrosion behaviors of B510L hot-rolled steel strips

The influence of oxide scales on the corrosion behaviors of B510L hot-rolled steel strips was investigated in this study. Focused ion beams and scanning electron microscopy were used to observe the morphologies of oxide scales on the surface and cross sections of the hot-rolled steel. Raman spectroscopy and X-ray diffraction were used for the phase analysis of the oxide scales and corrosion products. The corrosion potential and impedance were measured by anodic polarization and electrochemical impedance spectroscopy. According to the results, oxide scales on the hot-rolled strips mainly comprise iron and iron oxides. The correlation between mass gain and test time follows a power exponential rule in the damp-heat test. The corrosion products are found to be mainly composed of γ-FeOOH, Fe3O4, α-FeOOH, and γ-Fe2O3. The contents of the corrosion products are different on the surfaces of the steels with and without oxide scales. The steel with oxide scales is found to show a higher corrosion resistance and lower corrosion rate.