Electrochemical study of passive films formed on welded lean duplex stainless steel

The protectiveness and characterization of the passive film formed on Z3CN20.09M duplex stainless steel aged for different times were investigated by using electrochemical measurements and surface analysis method. The thermal aging causes the spinodal decomposition of the ferrite phase in the steel, resulting in the decrease of localized corrosion resistance. The increased aging time causes a thicker, dispersive, and lower resistance passive film formed on the surface of the steel based on EIS and Mott–Schottky (MS) analysis. The Auger electron spectroscopy (AES) and X‐ray photoelectron spectroscopy (XPS) results indicate that Cr is enriched in the inner layer of the passive films with a reduced content, decreasing the compactness and homogeneity of the passive films.

Section: Resultsmentioning

confidence: 99%

Passive film properties of Z3CN20.09M duplex stainless steel aged for different times

You

Chen

Yang

2018

“…Point defects present in the oxide film facilitate the diffusion of ions through the film. Mott–Schottky analysis was used for determination of defect density in the oxide film . In this process, the electrochemical system consists of two capacitances in series, that is, depletion layer capacitance C SC and Helmholtz layer capacitance C H. The capacitance value of Helmholtz layers (C H ) is always very high as compared to depletion layer capacitance C SC.…”

Section: Resultsmentioning

confidence: 99%

“…Mott–Schottky analysis was done by determining the capacitance at different potential. For this purpose electrochemical impedance measurement was done in the potential range −300 mV SCE to 1000 mV SCE at a step potential of 100 mV in borate buffer solution of pH 9.2 and capacitance was determined at 1000 Hz . Reciprocal of the square of capacitance was plotted against applied potential.…”

Section: Methodsmentioning

confidence: 99%

“…From the slope of this plot defect density (/cc) in the oxides of each cold worked sample was calculated using Mott–Schottky relationship (Eq. )

\frac{1}{C^{2}} = \frac{1}{C_{H}^{2}} + \frac{2}{ϵ ϵ_{0} q N A^{2}} true(E - E_{F B} - \frac{k T}{q} true)

where ϵ is the dielectric constant of the sample (15.6 for magnetite), ϵ o the vacuum permittivity (8.85 × 10 −14 ), q the charge, N the defect density, q the electronic charge (1.602 × 10 19 C), A is surface area of the specimen (cm 2 ), E FB the flat band potential, k the Boltzmann constant, T the absolute temperature.…”

Section: Methodsmentioning

confidence: 99%

“…Oxidation/corrosion kinetics of carbon steel by weight measurement as a function of time of exposure of the material to the process fluid has been reported earlier . The Mott–Schottky method is also extensively used for the determination of semiconducting property of the oxide film on metals and alloys and also for the determination of the defect density in the oxide film . There is no reported literature on the effect of cold working on the nature of oxide formed and its influence on FAC rate in carbon steel.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of cold working on oxidation behavior and nature of oxide film formed on carbon steel

Dubey

Roychowdhury

Kain

2017

Carbon steel is extensively used as a structural material in the secondary circuit of nuclear reactors. During fabrication of components such as elbows, T‐joint, expander/reducer, etc., the material is subjected to cold working. Aim of this study is to systematically investigate the effect of cold working on the oxidation behavior of carbon steel in alkaline environment at high temperature and pressure. Specimens from cold worked (up to 30%) carbon steel samples were oxidized in an autoclave at 270 °C for durations of up to 240 h in water of pH25 °C 10–10.2 obtained by adding lithium hydroxide. Oxidation rate, as calculated by weight gain, increased with extent of cold working. Potentiodynamic polarization and electrochemical impedance measurements were done in a borate buffer solution of pH 9.2 at room temperature, to characterize the oxide film formed on cold worked specimens. Impedance measurement followed by Mott–Schottky analysis showed that the defect density in the oxide increased with extent of cold working. Detailed examination established that the type and size of crystallites formed on the outermost oxide layer was the same irrespective of the extent of cold working.

Effect of the prior cold work on the corrosion resistance of lean duplex stainless steel welded by GMAW process

Souza

Soares

Faria

et al. 2018

The influence of the prior cold work (0, 10, 30, and 30% thickness reduction) on the microstructure evolution and corrosion resistance of UNS S32304 lean duplex stainless steel (LDSS) welded by gas metal arc welding (GMAW) process was investigated. The cold work promotes flattening of the ferrite and austenite bands, deformed regions in the austenite and increase of the hardness of the material. The welding of the cold‐worked steel generated, besides the typical regions of the welded DSS joints (fusion zone (FZ), heat‐affected zone (HAZ), and base metal zone (BM)), an annealed region around the HAZ, that showed partial recovery of the microstructure and hardness reduction. The HAZ presented excessive ferritization and precipitation of chromium nitrides. The cyclic potentiodynamic polarization tests, in an aqueous solution of 3.5 wt% NaCl at room temperature, showed for the only cold‐worked samples an increase of the pitting corrosion resistance up to a level of 30% thickness reduction and a decrease of the localized corrosion for 50% thickness reduction. The welding of the cold‐worked samples promoted the reduction of pitting corrosion resistance for all levels of thickness reduction evaluated.