Marangony effect in deep penetration laser welding of steel

Abstract

In deep penetration laser welding weld seam geometries can vary significantly although using the same process parameters and a steel with the same material number. One major reason for this can be the different content of additives like sulfur, phosphorus and even oxygen. These substances act as surfactants and even marginal changes of the chemical composition strongly effect the temperature dependent surface tension coefficient. In simulations of conventional and heat conduction laser welding the effect of the temperature dependent surface tension coefficient (Marangony effect) has been identified as the primary driving force of the liquid melt. In laser deep penetration welding simulations this effect has widely been neglected.In this contribution some simulations of melt pool flow fields resulting from various temperature dependencies of the surface tension coefficient are presented. The simulations confirm and clarify the observed variation in weld seam geometry due to very different flow patterns. These differences result from marginal fluctuations of the chemical composition that are within the tolerance of the standard defining the material composition of a special alloy. Therefore, it becomes clear that the chemical specifications for many steel alloys are too crude for reliable predictions of the seam geometry in deep penetration laser welding.In deep penetration laser welding weld seam geometries can vary significantly although using the same process parameters and a steel with the same material number. One major reason for this can be the different content of additives like sulfur, phosphorus and even oxygen. These substances act as surfactants and even marginal changes of the chemical composition strongly effect the temperature dependent surface tension coefficient. In simulations of conventional and heat conduction laser welding the effect of the temperature dependent surface tension coefficient (Marangony effect) has been identified as the primary driving force of the liquid melt. In laser deep penetration welding simulations this effect has widely been neglected.In this contribution some simulations of melt pool flow fields resulting from various temperature dependencies of the surface tension coefficient are presented. The simulations confirm and clarify the observed variation in weld seam geometry due to very different flow patterns. Th...