How To Avoid Internal Cracks in Square And Rectangular Tube?

What are the ways to avoid internal cracks in the square and rectangular tube?

1. Maximum deformation: The greater the maximum deformation, the better for continuous casting and rolling of the slab, but it also increases the possibility of internal cracks in the slab. How to improve productivity and produce the best maximum deformation without internal cracks for varied metallurgical circumstances needs to be explored and solved further.

2. The distribution of the amount of the reduction. The formed shell of square and rectangular tube is thinner towards the casting slab and the crystallizer. Because the temperature of the slab shell is higher, it is more favorable to inhibit the accumulation of strain and stress under the same deformation rate, therefore a higher compression rate should be utilized in the early stage of liquid core compression. Because of the thick solidification shell, the strain at the solidification front is relatively large in the late stage of liquid core compression, and because the temperature of the slab is decreasing, it is unfavorable to suppress the accumulation of strain and stress, so a lower compression rate should be used.

3. Reduced to a single roll. Due to the high temperature of the casting slab with liquid core, the strength of the square and rectangular tube billet shell is low, especially at the solidification front of the billet shell. Because of the deformation of the billet shell, cracks are easily formed at the incisions between dendrites in this location. When residual molten steel fills these cracks, the brittleness of grain boundaries increases due to segregation, and the cracks continue to expand, eventually forming internal cracks in the slab. As a result, the casting slab with liquid core should try to avoid large deformation during secondary cooling zone operation and limit deformation within the allowable range.