The surface defect of continuous casting slab is an important defect that affects the output of continuous casting machine and the quality of casting slab. According to statistics, cracks account for 50% of all kinds of defects. Cracks appear in the casting billet, which will lead to leakage or scrap in severe cases, and finishing should be carried out in light cases. This not only affects the productivity of the caster, but also affects the quality of the product, thus increasing the cost. The internal defects of the billet affect the mechanical properties, service performance and service life of the product. As shown in Figure 6-1, slab defects can be divided into the following three categories: continuous casting slab surface defects 1-corner transverse crack; 2-corner longitudinal crack; 3-surface transverse crack; 4-wide longitudinal crack; 5- Star-shaped cracks; 6—Vibration traces; 7—Blowholes; 8—Large inclusions
(1) Surface defects: including surface longitudinal cracks, transverse cracks, network cracks, subcutaneous slag inclusions, subcutaneous pores, surface depressions, etc.
(2) Internal defects: including intermediate cracks, subcutaneous cracks, depression cracks, inclusions, central cracks and segregation, etc.
(3) Shape defects: square billet deformation (out of square) and slab bulging.