Affecting Factors of Passivation Film on Stainless Steel Surface

Affecting Factors of Passivation Film on Stainless Steel Surface

Many people assume that stainless steel will not rust the name of stainless steel, but here Xiao Zheng wants Zheng Zheng to tell you: Stainless steel will rust! Because, in the actual use of the process, many factors will cause stainless steel passivation film to suffer damage, so that the passive state of stainless steel into a living state, resulting in decreased corrosion resistance of stainless steel, and then the occurrence of rust.
Which factors will destroy the stainless steel passivation film and cause stainless steel to rust?

1, Chloride ion
Chloride ion is a great hazard to stainless steel. In the passivation process, the chloride ion content in the passivation solution should be strictly controlled, and the passivation chemical material used requires a limited amount of chloride ions.
The preparation of passivation liquid water and cleaning water also have strict water quality requirements for chloride ions, so as to ensure that the passivated products do not adhere to chloride ions, so as to avoid future problems.

2,  The surface cleanliness
For stainless steel alloys, the lower the surface roughness, the smoother the surface, the harder the foreign matter, and the lower the chance of local corrosion of the various parts. Therefore, stainless steel should use a finished surface as much as possible.
In addition, stainless steel surface cleanliness is also very important, the final cleaning after passivation should be carefully carried out, because the residual acid to promote the cathode reaction, so that the film rupture, so that stainless steel activation, corrosion resistance decreased dramatically.

3, The use of environmental media
The passive film of stainless steel is a thermodynamically restrained metastable structure. Its protective performance is related to the environmental medium. During use, it should be cleaned regularly to remove harmful substances and be attached to the surface for a long time.
Especially in the environment with chloride ions, avoid the long-term milking of chlorine ions on the surface and concentrate in the water. For example, stainless steel is used in food industry. After each contact with food, it must be washed to avoid chloride ions and damage. Film.
For containers and equipment used in dairy products, the presence of chloride ions in dairy products has a destructive effect on the passivation film. For example, long-term storage of dairy products can lead to perforation of capacity and equipment. Therefore, regular cleaning is required to restore the passive film.

4,  The internal factors of stainless steel
Martensite content and chromium and nickel content in stainless steel have a great influence on the passivation performance of stainless steel. With low nickel content, the passivation performance is low. The passivation film performance of martensitic stainless steel is not as good as that of austenitic stainless steel.

Therefore, in the daily use of stainless steel, we must pay attention to the stainless steel use environment, according to the environment to choose the right type of stainless steel, which is very important!