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Apr 7, 2021
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The Causes and Control Measures of Four Major Surface Defects of Billets

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Surface defects of billets

1.Reconnect

1.1 Reasons for formation

a.Pouring is interrupted due to various operating failures, and reconnection defects are easily caused on the surface of the cast slab after re-pouring.

b.Slow drawing speed leads to too deep vibration marks on the surface of the cast slab, forming a reconnection.

1.2 Control measures

a.Fully do all the preparations for pouring steel to ensure the normality and stability of pouring steel, and avoid stop-flow accidents.

b.Ensure that the speed is normal and reasonable.

2.Inclusion and scarring

2.1 Reasons for 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 casting slab, and inclusions are formed on the surface of the casting slab.

b.The molten steel overflows at the drawing leak, is cooled by the mold, and forms defects on the surface of the cast slab.c. The drawing speed fluctuates excessively and frequently.

2.2 Control measures

a.Improve the technical quality and work responsibility of the operators, and ensure the stability of the crystallizer liquid level.

b.Improve the performance of the mold powder, increase the thickness of the slag layer, and increase the absorption capacity of inclusions.c. Strict process operation procedures, stable pulling speed.

  1. Improve the corrosion resistance of the tundish nozzle and plug.

3.scratches

3.1 Reasons for formation

  1. There is scrap steel on the foot roll of the second cold section frame, causing scratches on the surface of the cast billet.
  2. Uneven pulling and straightening rolls or uneven secondary cooling, causing the cast slab to deviate, and the casting slab and the pulling and straightening frame contact and scratch the surface of the cast slab.

3.2 Control measures

a.Strengthen the maintenance of the second cold section, and find that the steel breakout should be cleaned up in time.

b.Strengthen the maintenance of the tension-straightening system to ensure the levelness of the tension-straightening rollers, and install side guides to prevent the casting slab from deviating.

4.Vibration marks

4.1 Reasons for formation

a.Vibration marks are the inevitable result of mold vibration, and it is difficult to completely eliminate them. The greater the fluctuation of the mold liquid level, 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 vibration marks. Shrinkage-sensitive steel has deep vibration marks, and 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.

#Continuous casting

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