1. Chloride ion environment.
Chloride ions mainly exist in purified liquids and gases. Chloride ions will react with chromium ions in stainless steel, destroy the dense oxide film of stainless steel, and cause stainless steel to rust, thereby accelerating the corrosion of stainless steel, and even exceeding that of ordinary low-carbon steel.
2. Electrochemical corrosion.
When the surface of stainless steel is in contact with other metals for a long time, a primary battery will be formed in a humid environment, destroying the chromium oxide film and aggravating the rust of stainless steel.
3. Chromium does not meet the standard.
Chromium has a huge impact on the rust resistance of stainless steel. As the proportion of chromium increases, the steel is less likely to rust. Taking 304 stainless steel as an example, when the chromium content reaches 18%, its corrosion resistance suddenly changes, and the best corrosion resistance effect is obtained.
4. Surface scratches.
From a chemical point of view, the most unstable place is most likely to undergo chemical reactions. Surface scratches may also cause damage to the surface dynamic membrane. The scratched place becomes the most unstable place for stainless steel. Oxygen and water will enter the interior of the stainless steel and rust.
5. Mechanical stress.
When stainless steel is made into products, we need to go through processes such as stamping, shearing, punching, stretching, grinding, hot cutting, or welding. At this time, other metal elements, dust, or metal particles will be attached to the surface of the stainless steel, and they will produce chemical reactions when encountering chloride ions and sulfur ions in the air, thereby destroying the corrosion resistance of the stainless steel itself and accelerating the rusting process of the stainless steel.
6. Others.
The influence of organic acids, the influence of sulfides, etc., will destroy the passivation film of stainless steel.

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