The presence of surface active elements such as sulfur in steel, changes the surface tension on the weld pool surface.
The Marangoni effect induced by temperature dependent surface tension gradient, determines the direction of fluid flow
in the entire volume of the weld pool. The difference of initial sulfur concentration of the welded parts is an additional
factor which complicates the model. During welding an additional body force source term has been added to the momentum
equations at the liquid steel surface, depending on sulfur concentration gradient. Mutual mixing of welded steels in
the weld pool leads to periodic changes of driving force direction. The model permits the calculation of sulfur concentration
in the weld pool and weld size depending on the initial composition, laser power and welding velocity.
Key words: CFD, dissimilar welding, surface active element