Passive Layer Formation
Passive layer formation is the process where a thin, corrosion-resistant layer forms on metal surfaces. It prevents direct contact with the corrosive medium and protects the material.
Physical-Chemical Mechanism of Action
Passive layer formation occurs in many metals like steel when exposed to a corrosive environment (e.g., humid air). A typical example is the formation of an iron sulfide (FeS2) layer on steel. This process is triggered by a chemical reaction between the metal and oxygen in the medium.
Metallurgical Relevance & Welding Risks
The passive layer can be preserved with proper welding, enhancing the material's corrosion resistance. However, it can also break down under certain conditions (e.g., high humidity or excessive temperature), making the material vulnerable again. This can lead to accelerated corrosion, especially if the weld hasn't fully cooled.
Workshop Practice & Action Guidelines
To ensure strong passive layer formation, take the following steps:
• Use correct welding parameters and avoid overheating.
• Make sure the weld is completely cool before exposing it to a corrosive environment.
• For special metals or environments, always consult the manufacturer's guidelines on passive layer formation.