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What are the causes and characteristics of longitudinal cracks in continuous casting slabs

Update:04-11-2021
Summary:

1) Longitudinal cracks on the surface: ① Misalignment o […]

1) Longitudinal cracks on the surface: ① Misalignment of the nozzle and the mold causes bias current to wash the solidified shell; ② Poor melting performance of the mold powder, excessively thick or thin liquid slag layer, resulting in uneven slag film thickness, which makes the local solidified shell too thin. ③Mould page fluctuates; ④S+P content in steel. S in steel is greater than 0.02%, P is greater than 0.017%, the high temperature strength and plasticity of steel are obviously reduced, and longitudinal cracks tend to increase. ⑤ C in steel is between 0.12-0.17%, and the tendency of longitudinal cracks to increase.

2) Surface transverse cracks: ① Too deep vibration marks are the origin of the transverse cracks; ② The content of Al and Nb in the steel increases, which promotes the precipitation of the fingers at the grain boundaries and induces transverse cracks; ③ The billet is straightened at the brittle temperature; ④ Secondary cooling Too strong.

3) Surface net-like cracks: ①The surface of the high-temperature cast slab absorbs the copper of the mold, which turns the copper into liquid and then penetrates along the austenite grain boundary. ②The surface of the cast slab is selectively oxidized, so that the residual elements in the steel remain on the surface and penetrate along the grain boundary to form cracks.

4) Longitudinal cracks at the corners of the cast slab: For squares, the uneven thickness of the water gap along the height of the mold causes poor cooling of the corners of the mold; the mold taper is too small, and the mold fillet radius is too small. For slabs, it is due to ① improper support on the narrow side causing the narrow side to bulge. ②The taper is inappropriate. ③Who is not enough to cool the narrow surface?

5) Transverse cracks at the corners of the cast slab: ①The taper of the mold is too large. ②The surface of the mold is scratched. ③Inaccurate arc alignment between mold outlet and zero section.

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