Why is Stainless Steel Passivated?

To determine why stainless steels are passivated following the welding process, we first need to understand the meaning of a passive state along with how welding negatively affects this state. Passivation is important to maintain the quality of stainless steel.

Intro to Passivation

Corrosion resistance is one of the most important aspects of stainless steel to maintain. Without this, stainless steel will be exposed to wear over time. To make sure the stainless steel remains consistently corrosive, the surface of the material is manipulated to remain in a passive state. Passivation is one of the key reasons why stainless steel is capable of remaining corrosion resistant.

Stainless steel in a passive state requires a thin layer of chromium oxide formed on the surface, which is achieved specifically through the passivation process.

If you are considering passivation, you will discover that chelants, alkalines, wetting agents, and inorganic and organic acids are used regularly to keep the metal surface polished. As it’s exposed to oxygen, the metal forms the chromium oxide layer.

How Passivation Protects Against Welding Damage

Many people don’t understand that the default state for stainless steels is passive. However, once the steel is manipulated through welding or other processes, the surface becomes tarnished over time. To restore that much-needed chromium film, passivation, not deburring, is needed.

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Welding is actually one of the main reasons stainless steel requires passivation, as welded metal tends to lose its free iron from the alloy and the overall structure of the surface undergoes a transformation. Ultimately, the chrome to iron ratio decreases dramatically during welding, facilitating corrosion while forming a rougher surface. 

Passivation can help prevent this damage, but it isn’t without its setbacks.

Passivation Limitations and Deburring

The type of weld you use will determine if passivation is the right metal finishing process. While passivation eliminates most of the issues related to welding, the effectiveness of the passivation process on the whole depends on the quality of the weld.

In some cases, electropolishing may be a better process to use, particularly if there is heavy discoloration present following weld.

Electropolishing is an electrochemical process that can truly help improve the surface of stainless steel parts, giving them exactly what they need to withstand damage and wear from corrosion. The more corrosion resistance your parts have, the better they will perform, and electropolishing may help where passivation doesn’t.

Consult with Metal Finishing Professionals

If you want to determine whether or not your parts are compatible with passivation or may benefit from other services such as electropolishing, you’re better off consulting with professionals before making a decision.

The right company will be able to determine if this process is right for your parts or if another metal finishing process is required. This way you won’t need to worry about wasting money on insufficient services. In the end, you’ll see the benefits of using passivation along with other processes for stainless steel parts.

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