The increasing requirements for slab surface quality assurance in recent years reflect users’ requirements for higher quality steel. Bubbles and delamination are the two main surface defects of high-quality steel representative products-gapless steel. Bubbles are a common defect of gapless steel plates. They exist at a distance of 20 to 40 mm from the surface of the slab and have a size of about 500 mm. Delamination is a defect related to operating conditions, it contains alumina or powder. The non-metallic inclusions in the defective part are located less than 10mm away from the surface of the slab.
The non-metallic inclusions in the slab with a size greater than 100mm may cause cracks in the subsequent process. Pinholes associated with non-metallic inclusions may also cause delamination defects. In order to reduce the surface defects of the above-mentioned slabs, KEIJITSUNENAR and others of Japan Iron and Steel Corporation have taken the following measures: 1) Prevent or prevent non-metallic inclusions from being brought into the solidification process; 2) Entrainment control and control of non-metallic inclusions during the solidification process Separation; 3) Control the quality of the inner surface of the slab. Through theoretical analysis and field experiments, the use of vertical bending continuous caster and electromagnetic stirring in the mold and plasma EMC technology have improved the surface quality of the slab, and greatly reduced non-metallic inclusions; density and maximum particle size of non-metallic inclusions Under control, the cleanliness of molten steel has also been improved; and the use of plasma EMC technology can improve the quality of cast slabs and the stability of the meniscus of the mold.