What is the difference between passivated and unpassivated stainless steel?

What is the difference before and after passivation of stainless steel?

What is the change in performance?

What kind of applications are passivated products suitable for?

Passivation is one of the common surface treatment methods for stainless steel. Stainless steel products with this treatment tend to perform better in terms of corrosion resistance and salt spray test. Today, Faswell takes you to understand the surface passivation of stainless steel.

(A) stainless steel passivation principle

The corrosion resistance of stainless steel is mainly due to its surface covered with a very thin, dense passivation film, which separates the external oxidizing agent to play a role in corrosion resistance. Stainless steel can be naturally placed in the air to form a passivation film, but in the case of processing welding, assembly, scratches, oil contamination, etc., resulting in incomplete or defective oxide film, stainless steel is still at risk of corrosion.

The passivation treatment of stainless steel can form a high-density coverage on its surface, solid adhesion of good passivation film to ensure the integrity and stability of the passivation film, to achieve the purpose of effective protection of stainless steel.

In the case of 304 products, for example, without any surface treatment, the general salt spray test time of stainless steel screws is 48 hours, while the salt spray test time of passivated products can reach 1000 hours (except for carriage bolts).

(B) the use of stainless steel passivation scene

Stainless steel surface passivation is widely used in aerospace, automotive parts, precision hardware and other applications requiring high corrosion resistance, passivation of stainless steel with its excellent corrosion resistance can reduce the frequency of disassembly and replacement to ensure its stability and long-lasting use.

In special environments, such as in the ocean, coastal areas, humid environments and other applications, Shenzhen Lixin-iMachining Co., Ltd. recommends that stainless steel products take a surface passivation treatment to effectively extend the service life of the product. In the petrochemical industry, direct contact with petroleum or chemical agents of stainless steel, it is also recommended to passivate treatment to prevent direct contact reaction between stainless steel fittings and petroleum or chemical agents, resulting in product contamination.