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Two maraging steel rods with different sulfur content, deliberately seeded with alumina (Al2O3) inclusions, were remelted in an electron beam furnace. The aim was on one hand to highlight the emergence of non-metallic inclusions at the liquid metal surface and on the other hand to study the effect of the presence of a surface active element (sulfur) on their behavior. The in situ real time observation of Al2O3 clusters was possible using both high-speed video and infrared thermography. The inclusions emerge and tend to collide and quickly agglomerate into rafts. A semi-quantitative analysis confirmed that almost 100% of inclusions are captured at the free surface. The electron beam creates large thermal gradients in the impingement zones; this induces thermocapillary convection (Marangoni effect). The flow direction depends on the sulfur content. This tendency was well-observed by following the trajectories of inclusion rafts.