Sulfur Inclusions
Sulfur inclusions are reactions of dissolved sulfur with manganese to form manganese sulfides, which reduce transverse toughness.
Physico-Chemical Mechanism of Action
Dissolved sulfur reacts with manganese in the molten pool to form manganese sulfides. These sulfides are trapped in the structure during cooling and form stringers parallel to the weld.
Metallurgical Relevance & Welding Risks
The manganese sulfides reduce the toughness of the steel in the transverse direction, leading to stress buildup. This can result in cracks and hot cracking in the structure. Additionally, sulfur can act as a corrosive agent if it remains on the surface.
Workshop Practice & Action Guidelines
To avoid sulfide inclusions, use sufficient shielding gas (such as argon or helium) for the molten pool. The sulfur content in the steel should be kept below 0.02 %. If the sulfur content is high, chemical desulfurization before welding may be necessary.