(1) Surface pollution: The oil, dust, acid, alkali, salt, etc. attached to the surface of the workpiece are converted into corrosive media under certain conditions, and chemically react with some components in the stainless steel parts, resulting in chemical corrosion and rust.

(2) Surface scratches: The damage to the passivation film by various scratches reduces the protective ability of stainless steel, and it is easy to react with chemical media, resulting in chemical corrosion and rust.

(3) Cleaning: After pickling and passivation, the cleaning is not clean, resulting in residual liquid remaining, which directly corrodes stainless steel parts (chemical corrosion).

(4) Carbon steel pollution: The scratches caused by contact with carbon steel parts and the corrosive medium form galvanic cells and cause electrochemical corrosion.

(5) Cutting: The adhesion of rust-prone substances such as cutting slag and splashing and the corrosive medium form a primary battery to produce electrochemical corrosion.

(6) Baking school: The composition and metallographic structure of the flame heating area change unevenly, and form a galvanic battery with the corrosive medium to produce electrochemical corrosion.

(7) Welding: Physical defects (undercut, pores, cracks, lack of fusion, incomplete penetration, etc.) and chemical defects (coarse grains, poor chromium at grain boundaries, segregation, etc.) in the welding area and corrosive media form primary batteries Electrochemical corrosion.

(8) Material: Chemical defects (uneven composition, S, P impurities, etc.) and surface physical defects (porosity, blisters, cracks, etc.) of stainless steel are conducive to the formation of galvanic cells with corrosive media to produce electrochemical corrosion.

(9) Passivation: The passivation effect of pickling is not good, resulting in uneven or thin passive film on the surface of stainless steel, which is easy to form electrochemical corrosion.

(10) Cleaning: The remaining pickling passivation residue and the products of chemical corrosion of stainless steel form electrochemical corrosion with stainless steel parts.