One of the main defects on the surface of ultra-low carbon steel hot rolled coil is slag inclusion, the shape of the defect is generally black or black and white strip, and there is obvious color difference, intermittent distribution along the rolling direction, the length of the slag inclusion varies. The defects are mainly caused by the involvement of protection slag of mould in the continuous casting process. And found that the head billet, replace-nozzle billet and tail billet slag incidence is significantly higher than normal billet; when the liquid level fluctuations greater than ± 3mm, slagging rate increased by 50%.
How to reduce slag inclusion
- According to the law of defect occurrence, the head billet, the replace nozzle billet and level fluctuations billet and other non-stationary billet, flame cleaning mode can significantly improve the surface quality of hot rolled coil.
- The side holes of the dipping spout in the continuous casting process are prone to the formation of nodules, mainly due to ladle top slag, which disturbs the flow field of the mould and shall increase dipping depth. ﹛
- Adjusting the mould protection slag and optimize vibration mode to keep reasonable speed during non-stationary pouring ﹛
- The level fluctuation can be reduced through appropriate increasing the inclination of the nozzle, controlling the pulling speed, increasing the immersion depth of the nozzle optimizing the shape of the nozzle. ﹛﹛
- The mould blown into the bubble is to prevent the nozzle blockage, but the bubble will be rupture on the steel / slag interface to form foam slag. This foam slag is more likely to be caught into the liquid, the flow of argon shall be reduced as possible under the nozzle unblocked.
- The degree of superheat is an important parameter in the continuous casting process, when the superheat degree is increased to 30 ⊥ or more, the rate of inclusion defects can be reduced by about 30%. ﹛﹛
- If the viscosity of the protection slag is low, the slag will be caught in the mould along with the liquid.
