Stainless Steel Passivation ＂Black＂ Reason?

In the production process of stainless steel, passivation treatment is an important step. It can improve the corrosion resistance of stainless steel and extend its service life. However, sometimes we find that after passivation treatment, the surface of stainless steel appears a kind of "black" phenomenon. Do you know the reason? This article will reveal the reasons behind this phenomenon.

 

Firstly, we need to understand what passivation treatment is. Passivation treatment is a process that forms a stable and tight protective film on the surface of stainless steel to prevent metal from contacting with oxygen, moisture and other corrosive substances in the environment. This protective film can effectively prevent stainless steel from corrosion, improving its corrosion resistance and wear resistance.

 

However, during the passivation treatment process, a phenomenon known as "black passivation" may occur. This is because during passivation treatment, a layer of oxide film containing iron, chromium, nickel and other elements may form on the surface of stainless steel. The concentration of these elements in the oxide film is high, making the oxide film appear black. This phenomenon is particularly common in high-strength and high-hardness stainless steels.

 

So, what is the impact of this "black" passivation phenomenon on the performance of stainless steel?

 

Firstly, this "black" passivation phenomenon does not affect the corrosion resistance of stainless steel. Because this oxide film is formed by some elements of stainless steel itself, it has a good bonding force with stainless steel, which can effectively prevent stainless steel from corrosion.

 

Secondly, this "black" passivation phenomenon does not affect the wear resistance of stainless steel. Because this oxide film has high hardness, it can effectively improve the wear resistance of stainless steel.

 

However, this "black" passivation phenomenon may affect the appearance of stainless steel. Because it makes the surface of stainless steel appear black, it affects its aesthetics. Therefore, some industries or products with special requirements for stainless steel appearance may choose to avoid using this "black" passivated stainless steel.

 

So, how to avoid this "black" passivation phenomenon? At present, scientists are researching new passivation treatment methods, such as using passivating agents containing rare earth elements, or changing the process conditions of passivation treatment, in order to avoid or reduce the occurrence of this "black" passivation phenomenon.

 

In general, the "black" phenomenon after passivation of stainless steel is caused by the formation of a layer of oxide film containing iron, chromium, nickel and other elements during the passivation treatment process. Although this phenomenon does not affect the corrosion resistance and wear resistance of stainless steel, it may affect its appearance. Therefore, for industries or products with special requirements for stainless steel appearance, some measures need to be taken to avoid or reduce the occurrence of this "black" passivation phenomenon.