ABSTRACT
The molybdenum and nitrogen content of super austenitic stainless steel in Cl- solution is shown to influence pitting resistance using immersion, electrochemical testing, and simulation. Variations in Mo and N content affect the defect density, resistance, and densification of the passive film, thereby reducing the number of pitting. A higher local pH associated with the pitting pits and an increase in NH3(NH4+) are the results of increased N content, which also slows the rate of pitting expansion. The combined effects of fewer actively reactive spots within the passive film retarded pitting, and decreased corrosion rates due to NH3(NH4+) mitigation of local acidity which serves to reduce the corrosion rate. The work function is improved to a greater extent when Mo and N are co-doped compared with individual Mo and N doping, and the adsorption energy is significantly increased when Mo and N are co-doped, indicating a synergistic role for Mo and N in the prevention of corrosion by Cl-.
ABSTRACT
The effects of varying Cr and Mo concentrations on the pitting corrosion resistance of super austenitic stainless steels in Cl- solutions were investigated using a combination of immersion experiments, electrochemical measurements, X-ray photoelectron spectroscopy, and first-principles computational simulations. The surface characteristics, impedance, and defect concentration of the passive film were changed, and this eventually resulted in a decrease in the number of pitting pits. Due to a decrease in active sites within the passive film, a delayed beginning of pitting, and the combined effect of MoO42- inhibitors, it was discovered that an increasing Mo concentration slows the rate of pitting extension, resulting in reduced maximum pitting area and depth. Additionally, Mo increased the adsorption energy of nearby atoms, whereas Cr raised the adsorption energy of itself. Interestingly, compared with individual doping, co-doping of Cr and Mo increased work function and adsorption energy, indicating a synergistic impact in enhancing resistance to Cl- corrosion.
ABSTRACT
To provide a theoretical basis for the design of super austenitic stainless steel used in flue gas desulfurization environment, by changing the Cu content in 00Cr20Ni18Mo6CuN super austenitic stainless steel to explore the influence of Cu on its corrosion resistance, by electrochemical methods, XPS and first-principle computational simulations. The results show that Cu promotes the selective dissolution of Fe, Cr and Mo in stainless steel, and the copper content changes the proportion of compounds in the passive film, as well as its surface quality, resistance and defect density. The addition of one Cu atom increases the adsorption energy and work function of NH3 on Cr2O3 surface, reduces the charge transfer and hybridization. However, when the Cu content exceeds 1 wt%, the surface of the passive film is loose and has many defects. The appearance of oxygen vacancy and two Cu atoms leads to the decrease of adsorption energy and work function, and enhances the charge transfer and hybrid effect. The optimal Cu content is obtained through research, which not only improves the corrosion resistance of 00Cr20Ni18Mo6CuN super austenitic stainless steel in flue gas desulfurization environment, prolonging the service life of 00Cr20Ni18Mo6CuN super austenitic stainless steel, but also has practical application value.
