A: The cause of electrochemical corrosion of stainless steel parts is:
(1) Scratches caused by contact with carbon steel and corrosion medium form galvanic cells and produce electrochemical corrosion.
(2) Cutting: the adhesion of rusting substances such as slag and splash and corrosion medium to form galvanic cells and produce electrochemical rot.
(3) Baking: the composition of the flame heating area and the metallographic structure change and are not uniform, and the corrosion medium forms a galvanic cell and produces electrochemical corrosion.
(4) Welding: physical defects in the welding area (biting edge, porosity, cracks, non-fusion, non-penetration, etc.) and chemical defects (coarse grains, chromium-poor grain boundaries, segregation, etc.) form galvanic cells with corrosive media and produce electrochemical corrosion.
(5) Material: stainless steel chemical defects (uneven composition, S, P impurities, etc.) and surface physical defects (loose, sand holes, cracks, etc.) are conducive to the formation of galvanic cells with corrosive media and produce electrochemical corrosion.
(6) Passivation: pickling passivation effect is not good, resulting in uneven or thin passivation film on the surface of stainless steel, which is easy to form electrochemical corrosion. (7) Cleaning: The residual pickling passivation liquid is chemically corroded with stainless steel.
The principle is electrochemistry, that is, the galvanic cell mechanism, in which the galvanic cell is this steel, and as a negative electrode, carbon as a positive gas has a component reaction, so that the corrosion speed is accelerated.