Abstract: In order to compare the removal rates of liquid non-metallic inclusions and solid nonmetallicinclusions, the removal rates of four typical inclusions Al₂O₃，MgO-Al₂O₃，CaO-Al₂O₃-CaS and CaO-Al₂O₃ in pipeline steel during RH vacuum treatment were compared. The results show that solid inclusions in molten steel are easier to remove than liquid inclusions. In order to find out the reason why liquid inclusions are difficult to remove, the behavior of CaO-Al₂O₃ inclusions in molten steel at 1 600 ℃ was in-situ observed by high temperature confocal scanning laser microscope. The results show that this kind of inclusion is not easy to polymerize and grow up. With the decrease of temperature, the size of the inclusion further increases, and then it is captured by the solidified matrix. The CaO-Al₂O₃ type inclusions≥20 μm in casting slab can cause the large size inclusions exceed the standard in the hot rolled plate.

Key words: hot rolling steel, inclusions, formation, remove