Burnishing, also known as stainless rust, is a protective layer that is intended to reduce corrosion of ferrous components.
Burnishing is derived from the French "brunir", which means "to brown".
Burnishing takes place at relatively low temperatures of below 150°C, whereby oxygen is stored in the layer. Due to the low temperatures, the component is not exposed to high thermal stress.
In contrast to a coating, burnishing does not apply a layer of foreign material. The material of the component itself is changed on the surface.
Burnishing is carried out in one or more immersion baths in an alkaline medium. During burnishing, non-metallic layers with a thickness of about one to two micrometers are formed on the component.
Burnishing is limited to application to certain groups of materials, as it produces a chemical change in the surface. Unalloyed, low-alloy and hardened steels and cast iron are suitable. Stainless steel cannot be brownished in the classic process. The prerequisite for burnishing is clean, uncoated surfaces.
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