What are the defects of the slab during continuous casting?Continuous casting is just a maintenance. It is impossible to correct the problems of steelmaking an

What are the defects of the slab during continuous casting?

Continuous casting is just a maintenance. It is impossible to correct the problems of steelmaking and equipment. During the entire operation, there will be some defects in the slab, which affects the normal production. This is where we need to pay attention. It is better to understand the specific type. Operation.

  Slab defects:

  1, corner cracks. After the lower mouth of the crystal parts is severely worn, a larger air gap is formed between the mold copper tube and the casting billet, which forms a larger thermal resistance. As a result, the lower mouth is cooled too weakly and the billet shell becomes thinner. At the same time, due to the lower mouth Severe wear causes excessive cooling at the corners of the zero section, resulting in too large a cooling gradient from weak to strong cooling, resulting in stress concentration, and due to the uneven thickness of the blank shell, the casting billet becomes rhombohedral, which is easy to produce corner cracks.

  2, billet defects: middle cracks. When the cast slab passes through the secondary cooling zone, the cooling is uneven, and the thermal stress generated by the excessive temperature rise exceeds the maximum stress borne by the columnar crystals. In addition, the development of columnar crystals increases the probability of forming intermediate cracks.

  3. Depress cracks. Excessive pressure of the tensioning and correcting rolls will cause reduction cracks in the solid-liquid two-phase zone of the solidified casting slab. For the casting slab with developed columnar crystals and intermediate cracks, larger reduction cracks are often formed along the direction of the compaction.

  4. Loose center. The columnar crystals on both sides of the cast slab grow toward the center. When they meet together, they cause a "bypass", which prevents the molten steel above the bridge from supplementing the solidification and shrinkage of the molten steel below the bridge. When the molten steel under the bridge is completely solidified, many small particles are left Pores.

In particular, it is pointed out that the longitudinal cracks on the surface of the cast slab originate in the crystal parts. The thickness of the primary blank shell is uneven in the meniscus area. The tensile stress acting on the blank shell exceeds the allowable strength and strain of steel at high temperature. Stress concentration at the weak point leads to longitudinal cracks, which continue to expand in the second cold zone after exiting the mold.