Solidification of continuous casting billets will release much heat that divided three parts:
superheat of steel: the heat released from the cooling of the steel from the pouring temperature to the solidification temperature;
latent heat of solidification: the heat released from the cooling of the steel from the liquid phase temperature to the solid phase temperature;
physical sensible heat: the heat released from the cooling of the steel from the solid phase temperature to the room temperature. The rate of latent heat release is directly related to the productivity of continuous casting.
Solidification of continuous casting billets is a heat transfer process. Liquid steel is poured into the mould while heat transfer, solidification, and operation, forming a continuous casting billet with a fairly long liquid phase cavity. To accelerate the solidification of steel, there equiped three cooling zones:
Primary cooling zone: the steel is formed in the mould thick enough and uniform billet shell, to ensure that out of the mould does not pull leakage.
Secondary cooling zone: water spray cooling to accelerate the internal heat transfer to make the billet completely solidified.
Third cooling zone: to keep the billet at even temperature field.
When the billet is subjected to external forces (such as drum belly force, straightening force, thermal stress, etc.) exceeds the above critical value, cracks are generated at the solid-liquid interface and expand along the columnar crystal until the solidification shell can resist external forces. This is the reason for the internal cracking of the cast billet. The structure of continuous casting billet will change with the lowering of the temperature of the phase change, may occur sulfide, nitride plasmas in the grain boundary precipitation, increased high temperature brittleness, is the root cause of surface cracks in the cast billet.
