Causes and control measures of four major surface defects of billet

Surface defects of billets
1 Reconnect
1.1 Causes of formation
a. The pouring is interrupted due to various operating failures, and reconnection defects are likely to be caused on the surface of the slab after restarting the pouring.
b. Slow drawing speed leads to deep vibration marks on the surface of the slab, resulting in reconnection.
1.2 Control measures
a. Fully do all the preparatory work for pouring steel to ensure the normality and stability of pouring steel and avoid flow stoppage accidents.
b. Ensure that the pulling speed is normal and reasonable.

2 Inclusions and scars
2.1 Causes of formation
a. The liquid level of the mold fluctuates violently, so that the mold slag or other inclusions on the molten steel surface are involved in the slab, and inclusions are formed on the surface of the slab.
b. The molten steel overflows at the leak and is cooled by the mold, forming defects on the surface of the slab.
c. The pulling speed fluctuates too much and is frequent.
2.2 Control measures
a. Improve the technical quality and work responsibility of the operators to ensure the stability of the liquid level of the mold.
b. Improve the performance of mold slag and increase the thickness of the slag layer to improve the absorption capacity of inclusions.
c. Strict process operation rules and stable pulling speed.
d. Improve the erosion resistance of tundish nozzles and plugs.

3 Scratches
3.1 Causes of formation
a. There is scrap steel on the foot rolls of the frame of the second cooling section, causing scratches on the surface of the billet.
b. The unevenness of the pull-leveling rollers or the uneven secondary cooling causes the billet to deviate, and the contact between the billet and the pull-leveling frame scratches the surface of the billet.
3.2 Control measures
a. Strengthen the maintenance of the secondary cooling section, and clean up the broken steel in time.
b. Strengthen the maintenance of the tension leveling system to ensure the levelness of the tension leveling rolls, and install side guides to prevent the billet from deviating.

4 Vibration marks
4.1 Causes of formation
a. Vibration marks are the inevitable result of the vibration of the mold, and it is difficult to completely eliminate them. The greater the fluctuation of the liquid level of the mold, the deeper the vibration marks.
b. The slower the pulling speed, the lower the vibration frequency and the deeper the vibration marks.
c. The solidification characteristics of steel grades have a great influence on the vibration marks. Shrinkage-sensitive steel has deep vibration marks, while crack-sensitive steel has shallow vibration marks.
4.2 Control measures
a. Use low-amplitude, high-frequency sinusoidal vibration.
b. Take measures to ensure the stability of the crystallizer liquid level.