Control measures of slag inclusion on surface of low carbon aluminum killed steel plate

When producing aluminum-killed steel plates, one of the major defects on the surface of hot-rolled plates is slag inclusion, which will seriously affect the stability of production and the comprehensive finished product rate. It is considered that the TO content in the steel is unstable, and the effect of the slag inclusions after the calcium treatment is poor, and slag inclusions are likely to occur. At the same time, the unsuitable nozzles and the poor performance of the mold slag can lead to the occurrence of slag inclusions. The relevant control measures are:

1. Stable control of TO content in steel 1) Analysis of converter process with flue gas, smelting end point w(C)=0.04-0.06%, w(O)=(500-600)×10-6, temperature 1630-1650°C, The steel used for deoxidation with aluminum iron, ladle steel w (Als) = 0.015-0.035%, using the bottom slag detection and slag technology, ladle top slag layer thickness is not more than 50mm.

2) LF refining process, in-situ temperature sampling sampling, temperature rising and white slag desulphurization, control of LF top slag R=8-12, w(CaO)/w(Al2O3)=1.2-1.6; outbound steel control w(Ca)/ w(Als) = 0.08-0.10; the static flow of argon is 200L/min, and the time of argon blowing is 8-10min; ensure that the LF out of the station steel w(O) = (30-40) x 10-6.

3) Casting process ladle - tundish - crystallizer using argon protection casting, using argon purge before the open center, the middle package dry material w (MgO) ≥ 85%, the middle cover agent R = 8.0, reduce The secondary oxidation of aluminum in the steel ensures that w(O) = (25-35) x 10-6 in the medium cladding steel.

2. Optimization of immersible nozzle structure The immersion nozzle structure is improved through digital-analog calculation to reduce the surface fluctuation index of the molten steel, and the steel fluid level fluctuation index in the post-mold is improved by 80%, and the improved nozzle and mold width direction are improved. The liquid slag layer is relatively uniform and the thickness of the liquid slag layer near the narrow side can reach 6-8 mm.

3. Optimized performance of crystallizer protective slag During the casting of low-Carbon aluminum killed steel in thin slab, the protective slag has its unique performance requirements, and the protective slag layer can not be too thin. By increasing the content of MgO, the high temperature performance of the protective slag absorbing Al2O3 is improved. stability. The viscosity of the mold flux increases, the melting point decreases, the thickness of the liquid slag layer of the mold flux reaches 8-16 mm, and the entrainment of mold flux is effectively controlled.

In summary, the stability of TO content is controlled, the calcium treatment effect is stabilized, and slagging is avoided due to clogging of the nozzle; the nozzle mechanism is optimized to prevent mold scumming caused by too thin slag layer of the mold in the narrow side of the mold; and the performance of the mold is optimized. , Effectively control the entrainment of mold powder. For surface slag inclusions, the above control measures have achieved very good results.