Passive Layer
The passive layer is a thin, corrosion-protective oxide layer on stainless steels formed by chromium. It prevents further rusting and enhances rust resistance.
Physico-chemical mechanism of action
The passive layer forms on the surface of stainless steels through contact with oxygen, especially when chromium is present. This process creates a thin layer of chromium(III) oxide (Cr2O3) that acts as a strong oxidation barrier.
Metallurgical relevance & risks during welding
The passive layer can be preserved during proper welding and increase corrosion resistance. However, it can be interrupted by incorrect welding parameters or chemical environmental conditions, which can lead to corrosion. Too fast cooling or too high temperature can destroy the passive layer.
Workshop practice & instructions
To maintain the passive layer when welding stainless steels, the following measures should be taken:
• Use a protective atmosphere (e.g., argon purge) during welding.
• Keep the cooling steps slow and controlled.
• Avoid overheated tools or materials that could interrupt the passive layer.