A reactive molecular dynamics simulation study on corrosion behaviors of carbon steel in salt spray

Abstract

Corrosion behaviors, charge distribution, and oxide growth mechanisms of carbon steel have been studied by using reactive molecular dynamics simulations. The corrosion kinetics of carbon steel with a carbon content of 0.1% has been investigated in the 35‰ salinity salt spray with different densities of 1.03, 0.52, and 0.10 g/ml at different temperatures, respectively. The results show that the corrosion is massive in normal density (1.03 g/ml) salt spray system and pitting in dilute density (0.52 g/ml and 0.10 g/ml) salt spray systems. Iron crystal lattice defects on the carbon steel surface will arouse O, H, and Cl particles in the salt spray to migrate inward, causing deep oxidation. The density of salt spray is found to take a dominant position in the carbon steel corrosion. Therefore, the influence of temperature on oxidation kinetics in normal density salt spray is much greater compared to dilute density. In addition, the “decarburization” phenomenon of carbon steel has been observed and verified that the carbon content in the decarburized layer continues to decrease as the oxidation deepens. In the long-term simulation of the 1.03 g/ml salt spray system, the oxide growth and corrosion behavior are found to occur mainly before 600 ps, and the corrosion rate at this time is determined by the chemical reaction rate. After 600 ps, the corrosion rate depends on the electron diffusion rate. Furthermore, the activation energy is calculated to estimate the oxidizing property of different salt spray systems by fitting the consumption rate of water molecules into Arrhenius equation. When the concentration of salt spray decreases, the activation barrier tends to increase and the oxidizing ability of salt spray becomes weaker.