1. Pitting corrosion mechanism of 304 stainless steel cold rolled sheet
The corrosion resistance of stainless steel is mainly determined by the protective passivation film. However, due to the uneven defects, inclusions and solutes of the steel, when the medium contains some active anions (such as CI~ ions), these anions are first It is adsorbed on the metal surface at certain points, so that the film on the surface of the stainless steel is damaged. Once this layer of passivation damages and lacks the ability of self-forming, shoulder erosion occurs on the degrading surface of the stainless steel. This is because the rapid sinking of the metal surface is easy to reveal the basic metal, making it in an activated state, and the passivation film is in a passive state, which forms an active-passive etched micro-cell, so the corrosion develops deeper and the metal surface It is quickly corroded into small holes, that is, pitting corrosion.
2. CI~ion can cause pitting corrosion
Stainless steel can withstand very strong nitric acid, but cannot withstand relatively weak hydrochloric acid and dilute sulfuric acid. The C ions in hydrochloric acid and sulfur in sulfuric acid are all corrosion promoters of stainless steel. Especially after C ions are adsorbed on the metal surface, the compactness of the protective film on the surface of the stainless steel is destroyed, which can significantly accelerate the corrosion and make the surface of the stainless steel lose its protective effect. Lead to pitting corrosion on the surface of stainless steel. It can be seen from the energy spectrum curve of the sample that the corrosion of the sample contains C ions, that is, the C ions in the medium cause corrosion on the surface of the steel plate. 4.3 The influence of chemical composition on the passive film of stainless steel The corrosion resistance of stainless steel is mainly caused by the production of a chromium-rich oxide film with a thickness of more than 10A. The most effective way to increase the corrosion resistance of stainless steel is to increase the element chromium, molybdenum, and nickel content under certain conditions. Chromium increases the pitting corrosion resistance of steel, increases the chromium content in stainless steel, can increase the chromium content of the oxide film, and increase the chemical stability of the oxide film. The increase of the nickel content can avoid the reduction of the oxide film due to the enrichment of nickel under the film, thereby improving the stability of the film, and the increase of the content is particularly beneficial to improve the acid resistance of stainless steel. Aluminum's ability to be oxidized is between chromium and Shen.
3. The effect of surface finish of stainless steel on corrosion resistance
The surface finish of stainless steel has a certain influence on the corrosion resistance, and the improvement of the finish can improve the corrosion resistance. When the surface of stainless steel is rough, it is easy to accumulate scale on the surface, so it is easy to produce pitting corrosion.
4. Measures and suggestions to inhibit the corrosion of stainless steel at night
Because the medium contains CI~ ions, CI~ ions cause slight corrosion on the surface of 304 cold-rolled plates, and the rust is pitting corrosion caused by CI~ ions. In order to suppress the corrosion of stainless steel surface, the following measures are recommended:
1) Improve the chemical composition of 304 stainless steel, increase the content of chromium and nickel under certain conditions, increase the corrosion resistance of stainless steel and improve the structure of the passivation film.
2) Improve the surface finish of the 304 stainless steel cold-rolled sheet, and the improvement of the finish can improve the corrosion resistance.
3) In order to prevent the stainless steel surface from being contaminated by scale or rust to cause pitting corrosion, the user must ensure that the stainless steel surface is clean and dry, and provide a good environment to avoid corrosion of the steel plate surface.