Decarburized surface layer
The decarburized rim is a surface zone where carbon has escaped from the steel during heat treatment in an oxygen-containing atmosphere. This leads to a reduction in strength and fatigue strength at the surface.
Physicochemical mechanism of action
During heat treatment in an oxygen-containing atmosphere, carbon reacts with oxygen and escapes as a gas. This process occurs mainly in the surface zone of the steel, leading to decarburization.
Metallurgical relevance & risks in welding
The decarburized rim reduces the strength and fatigue strength of the surface. This can lead to cracks and fracture under mechanical stress. Furthermore, it can affect the behavior of the steel under stress, which can be problematic especially in highly loaded applications.
Workshop practice & instructions
To avoid the decarburized rim, heat treatments should be performed in a protective gas atmosphere (e.g., argon). For existing parts, fine polishing or surface finishing can improve the surface and reduce the risk of cracking and fracture.