Abstract: The inclusions of EH36 ship plate steel produced by “BOF→LF→RH→CC” process were studied. The morphology and composition of inclusions in the sample were analyzed by SEM-EDS，and the precipitation of inclusions were calculated by Factsage software. The research showed that inclusions were mainly SiO₂ when the molten steel was hoisted into LF furnace，and MnS of the sample was formed during solidification of the sample. The number of liquid inclusions was increased after calcium treatment. Al₂O₃ content of inclusions was increased and the content of CaO and MgO were decreased after RH refining. Al₂O₃ content of inclusions was decreased and CaO content of inclusions was increased in tundish. The composition of inclusions was close to the low melting point zone due to the inclusions reacting with slag. SiO₂ content of slag was high and it reacted with Al of molten steel，which caused to increase Si content and reduce Al content in the molten steel. Because composition segregation occurred during solidification of molten steel，S content of inclusions was significantly increased，Al₂O₃ content of inclusions was increased and CaO content of inclusions was decreased. Calcium aluminate inclusions with different ratios of CaO and Al₂O₃ and Al₂O₃ inclusions were formed in the billet，and CaS was formed on the surface of some calcium aluminate.

Key words: ship building steel, inclusion, continuous casting slab, slag, sulfide