Residual Sulfur Influence
Residual sulfur influence: Sulfur contents in the melt can form manganese sulfides, which as lines in rolled microstructures lead to anisotropic toughness. Dissolved sulfur also lowers surface tension and affects penetration depth in welding.
Physical-Chemical Mechanism of Action
Residual sulfur in the melt reacts with manganese to form manganese sulfides. These form as stringers in the rolled structure and lead to anisotropic toughness, making stress transfer uneven. Dissolved sulfur lowers the surface tension of the melt, which raises the fluidity limit and affects penetration depth during welding.
Metallurgical Relevance & Welding Risks
Too high a residual sulfur content can form manganese sulfides, leading to anisotropic toughness and uneven stress transfer in the structure. This increases the risk of cracks and hot cracks. Dissolved sulfur lowers surface tension, raising the fluidity limit and affecting penetration depth during welding. Too high a penetration depth can cause stress buildup and lead to cracking.
Shop Practice & Action Items
To minimize the effect of residual sulfur, keep the sulfur content in the melt below 0.1 %. This can be achieved by careful selection of the steel and use of deoxidizers. During welding, watch that the penetration depth is not too high to avoid stress buildup. A penetration depth of 1-2 mm is generally safe.