1.4 Selection of treatment methods
Which method is used for the surface treatment of stainless steel fabrication, according to the product structure, material, and different requirements on the surface.
2 Common causes of corrosion in stainless steel fabrication parts
2.1 Chemical corrosion
2.1.1 Surface contamination: oil, dust, acid, alkali, salt, etc. attached to the surface of the stainless steel fabrication workpiece are converted into corrosive media under certain conditions, and chemically react with certain components in the stainless steel to cause chemical corrosion and rust.
2.1.2 Scratch on the surface: damage to the passivation film caused by various scratches, so that the protection ability of the stainless steel is lowered, and it is easy to react with the chemical medium to cause chemical corrosion and rust.
2.1.3 Cleaning: After washing and passivation, the cleaning is not clean, leaving residual liquid, directly lead to corroding of stainless steel fabrication parts (chemical corrosion)
2.2 Electrochemical corrosion
2.2.1 Carbon steel pollution: Scratches and corrosive media caused by contact with carbon steel parts and then form galvanic cells and cause electrochemical corrosion.
2.2.2 Cutting: adhesion and corrosion of rust-prone substances such as slag and splashing form a primary battery to produce electrochemical rot.
2.2.3 Heat correction: The composition of the flame heating zone changes and the metallographic structure is uneven, and the primary battery is formed with the corrosive medium to cause electrochemical corrosion.
2.2.4 Welding: Physical defects (biting, stomata, cracks, unfused, incomplete penetration, etc.) and chemical defects (grain coarse, grain boundary chrome, segregation, etc.) and corrosive media form galvanic cells and cause electrochemical corrosion .
2.2.5 Material: Stainless steel chemical defects (uneven components, S, P impurities, etc.) and surface physical defects (loose, sand holes, cracks, etc.) are conducive to the formation of galvanic cells with corrosive media to produce electrochemical corrosion.
2.2.6 Passivation: The acid passivation; 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.
2.2.7 Cleaning: The remaining of acid-washed passivation and the chemically corroded product of stainless steel form an electrochemical corrosion with the stainless steel piece.
2.3 Stress concentration is prone to stress corrosion.
In short, due to its special metallographic structure and surface passivation film, stainless steel is generally difficult to be corroded by chemical reaction with the medium under normal conditions, but it cannot be corroded under any conditions. In the presence of corrosive media and incentives (such as scratches, splashes, slag, etc.), stainless steel can also be corroded by slow chemical and electrochemical reactions with corrosive media, and the corrosion rate is relatively fast under certain conditions. Corrosion, especially pitting and crevice corrosion. The corrosion mechanism of stainless steel fabrication parts is mainly electrochemical corrosion.
Therefore, all effective measures should be taken during the processing of stainless steel products to avoid rust conditions and incentives. In fact, many rust conditions and incentives (such as scratches, splashes, slags, etc.) have a significant adverse effect on the appearance quality of the stainless steel fabrication product and should and must be overcome.