Severe Mn vaporization for partial-penetrated laser keyhole welds of high-manganese cryogenic steel

The study analyzed the vaporization characteristics of Mn during the laser welding of high-manganese (Mn) cryogenic steel, focusing on the effect of the focal position. The volume of fluid method and transient computational fluid dynamics simulations were used to analyze the molten pool behavior. The keyhole formation process and keyhole wall temperature induced by the focal position were investigated to understand the mechanism behind the varying amounts of Mn vaporization depending on the degree of laser penetration. The reduced defocus distance of laser beam (least defocused; LD) produced the high energy density and complete penetration, less multiple reflection of laser beam, low keyhole-wall temperature, therefore exhibiting the minor Mn vaporization. The electron probe microanalysis results and the analytical model used in this study were highly congruent, confirming the most significant Mn vaporization in the partial-penetrated welds of keyhole formation (medium defocused; MD).