Research of initial stages of the local corrosion process of chromium steel (13% Cr) by the methods of atomic force microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy

By the methods of atomic force microscopy (AFM), Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) the initial stages of process of local electrochemical corrosion of chromium steel (13% Сr) was investigated. It is established, that pittings occurs already on the first minute of corrosion. The most informative statistical parameters and optimum scale of АFМ images are certain. According to ОЭС there is a reduction of the Cr concentration and increase in concentration of the Fe in pittings in comparison to a matrix as a result of the corrosion processes. By method XPS it is established, that as a result of local corrosion there is an increase in concentration of chrome in surface layers of steel due to dissolution of the adsorbed layers. In depth of samples with increase the time of corrosion, the decrease in concentration of chrome as a result of local anode dissolution is observed. As the increase relative concentration of the iron in all layers of samples after corrosion, in comparison with the initial sample is noted. It is connected with dissolution of the adsorbed layers and decreasing of the chrome concentration during local corrosion. XPS data confirm, that local corrosion of investigated steel begins already with the first minute of tests to what occurrence in XPS spectra of a line of metal chrome. This effect can be an attribute of the beginning of the local corrosion processes. The concentration of the chrome oxides decreases from surface to deeper layers (up to 40 nm). This phenomenon in a greater degree is shown for samples after corrosion.