The main reasons for rust after passivation of stainless steel are as follows:
Passivation layer damage: Once the stainless steel passivation layer is damaged by scratches, abrasion or chemical corrosion, the metal surface will be exposed to the external environment, lose protection, and is prone to rust reaction. Therefore, maintaining the integrity of the passivation layer is key to preventing stainless steel from rusting.
Oxidizing gases: In environments with high oxygen content and high concentrations of oxidizing gases in the air, the stainless steel passivation layer is susceptible to oxidative damage, resulting in rust. Oxygen reactions in an oxidizing environment can destabilize the passivation layer and promote rust of stainless steel.
Chloride plasma: The environment containing chloride plasma can damage the passivation layer of stainless steel, resulting in intergranular corrosion of stainless steel, which can lead to rust. The presence of chloride destroys the protective effect of the passivation layer on the metal, exposing the stainless steel to corrosive media.
Foreign body contamination: When the surface of stainless steel is contaminated by organic matter, dust or other foreign matter, it may cause damage to the passivation layer, making stainless steel prone to rust reaction. Therefore, keeping the stainless steel surface clean is an important measure to prevent foreign body contamination.
Wrong handling: Incorrect passivation treatment methods or parameter settings may lead to poor quality and damage to the passivation layer, which can promote the occurrence of rust. Therefore, the passivation process needs to be carried out in strict accordance with the operating procedures to ensure the quality and stability of the passivation layer.
In summary, factors such as damage to the stainless steel passivation layer, environmental oxidation, the presence of chloride ions, foreign body contamination, and improper treatment may cause rust to still appear after stainless steel passivation. Therefore, the correct maintenance and protection of the passivation layer and the avoidance of adverse environmental factors are the key measures to prevent stainless steel rust.