Abstract: Maraging steel,as a representative ultra-high-strength steel,is highly sensitive to the influence of nonmetallic inclusions on its mechanical properties.In this study,00 Ni18Co8Mo5TiAl steel was selected as the material,and a steady static magnetic field was applied outside the insulated melt to regulate melt flow via the magnetic damping effect and thereby promote the aggregation and removal of inclusions.Systematic investigations on the types,sizes,and number densities of inclusions under different conditions were performed through the industrial sampling and remelting experiments.The obtained results show that the inclusions in industrial samples were mainly TiN and TiS with a small amount of Al₂O₃ and complex inclusions.Among the inclusions,TiN exhibited a number density of approximately 230 mm^-2 with an average size of 0.67μm,while TiS had a number density of about 220 mm^-2 and an average size of 0.9μm.Remelting experiments revealed that,compared with samples without magnetic field application,the inclusion number density decreases from 139 mm^-2 to 96 mm^-2,whereas the average size increases from 1.01μm to 1.57μm,with a significant reduction in TiS inclusions.Furthermore,Al₂O₃ enrichment on the surface becomes to be more pronounced under the magnetic field application.Mechanism analysis indicates that the static magnetic field suppresses melt convection,stabilizes the gas-liquid interface,and prolongs the interaction time between the melt and the atmosphere,thereby enhancing the removal of Al.Meanwhile,the magnetic damping effect restrains solute diffusion,reduces TiS nucleation,and facilitates the Ostwald ripening process.This leads to a decrease in inclusion number density but an increase in size.Theoretical calculations further indicate that both TiS and Ti₄C₂S₂ can stably precipitate in molten steel;however,when the sulfur content is below 0.002%,the precipitation of TiS is significantly suppressed.