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In the current study,the transformation in the composition of non-metallic inclusions from the molten steel to the solidified steel was studied and the composition distribution of inclusions on the cross section of a linepine continuous casting slab was predicted.During cooling and solidification of the continuous casting strand,Al2O3-CaO inclusions reacted with the bulk steel and transformed to CaS-Al2O3-MgO-(CaO) ones in the continuous casting slab.The composition of inclusions on the cross section of the slab varied with locations due to the varied cooling rate.A model was established to predict the distribution of the composition of inclusions on the cross section of the continuous casting slab,coupling solidification and heat transfer of the continuous casting slab,the kinetic mass transfer of the dissolved elements in the solid steel,and thermodynamic calculation of inclusion transformation at different temperatures.The composition transformation of inclusions mainly occurred at the temperature between the liquidus and solidus of the linepipe steel.Inclusions were mainly CaS-Al2O3-MgO-(CaO) in slab center and were MgO-Al2O3-CaO-CaS within the subsurface of the slab.In the slab,the transformation fraction of inclusions was less than 10％ at corners while it reached 70％ at 50 mm below the surface of the slab.