Lämpöpassivointi

Lämpöpassivointi is a heat treatment process used to improve the corrosion resistance of stainless steel. It is particularly effective in removing free iron from the surface of the material, which is often present after mechanical processing steps such as welding, grinding, or polishing. Free iron on the surface of stainless steel can oxidize and form rust, compromising the aesthetic and protective properties of the material.

The process involves heating the stainless steel to a specific temperature, typically between 350 and 450 degrees Celsius, in a controlled atmosphere, often a vacuum or a reducing atmosphere like hydrogen. During this heating phase, free iron atoms at the surface diffuse into the bulk of the material or react to form a stable chromium oxide layer. This diffusion or reaction effectively removes the susceptible free iron from the surface.

Following the high-temperature treatment, the material is cooled. The resulting surface is characterized by a passive chromium-rich oxide layer that is integral to the stainless steel itself, rather than a superficial deposit. This makes the passive layer highly resistant to corrosion and wear.

Lämpöpassivointi is a valuable post-processing step for stainless steel components that require a high level of corrosion resistance, especially in demanding applications such as the food and beverage industry, medical equipment, and chemical processing. It is an alternative or complementary process to traditional chemical passivation, offering a different mechanism for surface treatment. The specific parameters of temperature, time, and atmosphere are carefully chosen based on the grade of stainless steel and the desired outcome.