Mould protection slag has the following five major functions to benefit the billet production.
1. Reduce the heat loss of the molten steel
Continuous casting protection slag must have good adiabatic thermal insulation properties, so that the continuous casting process can inhibit the formation of bridges and crusts in the mould, while increasing the temperature of the surface, so that the growth of the billet surface is smooth, but also able to make a larger radius of curvature. Along with the increase in the radius of curvature of the surface, from the lower mould steel bubbles and oxide inclusions are not easy to be captured by the surface, easier to float to the liquid slag layer, thus making the steel more clean.
2. Prevent secondary oxidation
Protective slag in the steel under the action of high temperature, will quickly form a liquid slag layer, can impede the diffusion of air to the steel surface. Using the three-layer structure of the protective slag on oxygen, nitrogen isolation, so that the steel from secondary oxidation and absorption of nitrogen, not only to prevent secondary oxidation of the steel, to avoid the oxidation of alloying elements in the steel, but also play a role in preventing the steel from the air to absorb nitrogen, which is conducive to improving the cleanliness of steel.
3.Reduce the casting billet bonding
Good lubrication between the mould copper plate and the casting billet can reduce mutual friction, improve the life of the mould and prevent steel leakage accidents. In the mould around the bending surface, due to the vibration of the mould and the capillary effect of the gap between the billet shell and copper plate, the liquid slag formed by the melting of the protection slag is sucked and filled with the gap between the copper plate and the billet shell, forming a slag film, play a lubricating role.
4.Improve the mould heat transfer
In the mould the shrinkage of the billet shell produced an air gap, so that the thermal resistance increases. Add protection slag, so that the air gap is filled with uniform slag film, can reduce the air gap thermal resistance, significantly improve the heat transfer of the mould, so that the billet shell growth uniform.
5. Absorb non-metallic inclusions
Research shows that the addition of relatively large ionic radius of alkali metal compounds in the continuous casting protection slag can reduce the viscosity of the protection slag and improve the ability of the liquid slag to absorb inclusions.
