Solidification of continuous casting billet

The products produced by continuous casting include round billet, square billet, slab and various near-net-shape products (thin strip, special-shaped billet, etc.). Using continuous casting billet instead of die casting as rolling material has significantly improved the yield of steel from a process point of view because the continuous casting process completely eliminates the problems of gating system and riser cutting, which increases the yield rate by about 10%~15%.

continuous casting process>>>

1. Drawing speed control

On the premise of ensuring the quality of the billet and safe production, the drawing speed is mainly restricted by the solidification speed of the billet.

The relationship is: s=Kt½

Where s is the thickness of the steel solidification layer (mm), and s is the solidification time (min). A certain s value should ensure that the hard shell does not break and safe production, and the K value is 23~32, depending on the steel type, section, molten steel temperature and drawing speed changes.

Taking ordinary carbon steel as an example, the billet drawing speed is:

Slab 0.5~1.8 m/min, billet 0.6~1.5 m/min, billet 1.5~3.5 m/min, CSP4.5~6 m/min.

2. Cooling control

The cooling area of continuous steel casting is concentrated in three parts: CCM tube, secondary cooling section and post-process cooling (air cooling). It is generally believed that the crystallizer section accounts for 14~20% of the cooling amount, and the secondary cooling section accounts for 23~30%. When the cooling intensity is too large and the drawing speed is not suitable, it will cause internal and external cracks in the billet. If the cooling intensity is too small and uneven, it is easy to cause billet bulging, steel leakage and other phenomena. The cooling intensity must be controlled and adjusted according to the steel type, billet temperature and drawing speed. The cooling water consumption per kilogram of steel is about 1~2 kilograms. Each section is required to be cooled evenly, and the cooling water must be filtered and purified to make the water clean and the heat conduction uniform.

3. Heat transfer and shell thickness in the continuous casting mould

During continuous casting, the total heat (Qsum) released by the molten metal is transferred from the mould boundary to the cooling water in a very complex process. There are several heat transfer modes at the molten metal and mould boundary at the same time. The protective powder and air gap form boundary thermal resistance, which hinders the heat transfer between the molten metal and the mould boundary.

Under stable production conditions, the total heat Qsum released by the molten metal inside the mould can be estimated, and this part of the heat is taken away by the cooling water.