Sulfur Segregation in Primary Microstructure
Sulfur segregation is a local enrichment of sulfur at grain boundaries during solidification, which forms low-melting eutectics and increases hot cracking tendency in welding.
Physico-chemical mechanism
Sulfur segregation happens when sulfur vapors concentrate locally at grain boundaries during solidification of the metal. This leads to the formation of low-melting eutectics that are liquid at low temperatures.
Metallurgical relevance & welding risks
The low-melting eutectics make the metal particularly sensitive to hot cracking at these points. If cooling is too fast, these eutectics can suddenly solidify and cause cracks. This increases the likelihood of hot cracks in the weld.
Workshop practice & actions
To minimize sulfur segregation, the metal should be well protected from sulfur vapors during solidification. When welding, controlled cooling is essential. Use a long cooling path and keep the weld warm until it has completely cooled down (approx. 30-60 minutes). Check the metal for hot cracks after welding.