Sulfur segregation band
Sulfur segregation band is a zonal concentration of sulfur in steel or sheet that causes mechanical weak points and leads to cracks under load.
Physico-chemical mechanism
The sulfur segregation band is formed by the concentration of sulfur in certain areas of the material. This can be caused during the melting process or by chemical reactions in the metal. Sulfur forms molecules that consolidate on specific crystal faces, creating zones with increased sulfur concentration.
Metallurgical relevance & welding risks
These sulfur zones are mechanically weak and can crack under thermal stress, e.g., during welding or stress relief tests. Cracks occur due to the attraction between sulfur molecules and the metal crystal lattice, destabilizing the structure.
Workshop practice & actions
To avoid or minimize sulfur segregation bands, ensure a clean melting process and environment. Use high-quality raw materials and carefully control chemical composition. When welding steels with a known sulfur segregation band zone, use specific welding methods like gas welding or TIG welding to control temperature and stress. If suspected, a metal analysis is required to determine sulfur concentration and take appropriate action.