The causes and preventive measures of transverse cracks in the corners of continuous casting billets mainly include the following points:
Steel composition:
Carbon content: During the solidification process of hypoperitectic steel with a carbon content of 0.10%~0.15%, due to the volume shrinkage accompanied by the δ→γ transformation, air gaps may be formed between the billet shell and the copper plate, which will reduce the billet shell temperature, increase the coarseness of austenite grains, and reduce the high-temperature plasticity of steel.
Sulfur content: Too high sulfur content will form (Mn,Fe)S inclusions, reduce the grain boundary strength, and increase the hot brittleness of steel.
Secondary cooling conditions:
Uneven cooling: The secondary cooling nozzle is seriously blocked, resulting in uneven cooling of the billet surface, especially overcooling of the corners, which is very easy to cause surface transverse cracks.
Crystallizer vibration:
Oscillation mark depth: Too deep vibration mark depth, especially the high-frequency and small-amplitude sinusoidal vibration mode, can suppress the notch effect of deep vibration mark trough on cracks.
Continuous casting machine accuracy:
Bill position deviation: The billet position is not in the center of the continuous casting machine, but is about 10mm to the east, resulting in the billet at the west corner being in the middle of the nozzle, increasing the cooling intensity of the corner and enhancing the crack sensitivity.
Other measures:
Control the nitrogen content in steel: Control the nitrogen content in steel below 60ppm through refining micro-positive pressure operation, continuous casting full-process protection casting and other measures to reduce the precipitation of AIN.
Ground slow cooling measures: Reduce the temperature of the billet entering the heating furnace, ensure that the surface temperature of the billet is lower than 600℃, and control it at around 500℃, so as to promote the dispersion of AIN particles into the austenite grains and inhibit the weakening effect of AIN particles on the grain boundaries.
The above measures can effectively prevent the occurrence of transverse cracks in the corners of the continuous casting billet and improve the overall quality and production efficiency of the continuous casting billet.
