Continuous cast slab and method for manufacturing the same
Provided is a continuous cast slab and a manufacturing method for the same, wherein solidified layers of a cast slab having a non-solidified layer are compressed with each other during a continuous casting process to fundamentally prevent occurrence of defects, such as center segregation or porosity, which deteriorate quality of the cast slab, thereby decreasing defects. A continuous casting method for producing a cast slab by drawing molten steel from a mold includes preparing a compressing unit, and reducing at least one side of the drawn cast slab by using the compressing unit, wherein solute-enriched residual molten steel is caused to flow back in a direction opposite to a casting direction. Thus, it is possible to produce a cast slab wherein defects such as center segregation are greatly eliminated.
1. A method for manufacturing a continuous cast slab with a thickness of 100 mm or more using a continuous casting machine,
wherein when a cast slab is continuously casted using at least one segment having a plurality of upper and lower rolls facing each other in a thickness direction of the cast slab, a region of which solid fraction is in the range of 0.05˜0.2 to 0.3˜0.6 in a center portion of the cast slab is reduced in the thickness direction of the cast slab, a reduction gradient of the segment is set to 5 to 20 mm per 1 m length in a casting direction, and a reduction amount of the segment is increased along downstream of the casting direction to let solute-enriched residual molten steel flow back to a molten steel free flow region toward an opposite direction to the casting direction so that the center portion of the cast slab has negative segregation.
2. The method as claimed in claim 1 , wherein there are provided at least two segments, and the segments have the same reduction gradient or different reduction gradients.
3. The method as claimed in claim 1 , wherein there are provided at least two segments, and among the segments, the segment located downstream in the casting direction has a greater reduction gradient than the segment located upstream in the casting direction.
4. The method as claimed in claim 1 , wherein a final roll of the segment has a reduction ratio of 0.9 to 1.1.
5. The method as claimed in claim 1 , wherein when the cast slab has a center solid fraction of 0.3 to 0.6, a solid fraction of the cast slab compressed in the thickness direction is 0.9 or more.
6. The method as claimed in claim 1 , wherein a reduction rate of the cast slab by the segment is 3 to 30 mm/min.
7. The method as claimed in claim 1 , wherein an overheating temperature of the molten steel is less than 20° C. before the molten steel is inputted into a mold of the continuous casting machine.
8. The method as claimed in claim 1 , wherein at least one edge of the cast slab is chamfered by using a mold of the continuous casting machine conforming to the chamfered shape.
9. The method as claimed in claim 1 , wherein at least a part of solute-enriched residual molten steel remaining in the center portion of the cast slab with a solid fraction of 0.3 to 0.6 is moved to a region of the center portion with a solid fraction of 0.2 or less.
10. The method as claimed in claim 1 , wherein at least one electromagnetic stirring unit is installed between a mold of the continuous casting machine and the segment to stir the backflow molten steel in the cast slab by electromagnetic force.