Effect of corrosion inhibitor on corrosion behaviour of 15CrMo in NH 4 Cl solution by electrochemical method

In this study, the effects of different corrosion inhibitors and concentrations on the corrosion behaviour of 15CrMo steel in NH4Cl solution were systematically investigated by combining electrochemical testing with surface morphology analysis. The results show that the corrosion inhibitor can effectively inhibit the corrosion of 15CrMo steel, which is manifested by the decrease of self-corrosion current density, the increase of charge transfer resistance, and the improvement of surface morphology. Inorganic corrosion inhibitors have a wide concentration window, and their properties are insensitive to concentration changes. In contrast, organic inhibitors exhibit a pronounced optimal concentration effect, where performance is highly dependent on precise concentration control. For example, there was a clear optimum concentration (0.04 g/L) of sodium dodecyl sulphonate (SDS2). After this concentration, the density of the adsorption layer decreases due to the excessive adsorption of interface molecules, and the corrosion inhibition rate decreases. Therefore, the strategy for precise concentration control is highly dependent on the specific molecular structure of the corrosion inhibitor. This study provides a theoretical basis and practical guidance for the corrosion protection of 15CrMo steel in NH4Cl solution, which is helpful to optimise the selection and concentration of corrosion inhibitors and reduce the corrosion risk.