What is the function of continuous casting slag?
Release time:
2020-12-29
1. Continuous casting flux What is its function?
During casting, powdery or granular slag materials are continuously added to the surface of the molten steel in the mold. This is called protective slag. The functions of protective slag are as follows:
(1) Heat insulation and heat preservation to prevent heat dissipation.
(2) Isolating the air to prevent oxygen in the air from entering the molten steel and causing secondary oxidation, affecting the quality of the steel.
(3) Absorbing and dissolving inclusions that float from the molten steel to the interface between the steel and slag, purifying the molten steel.
(4) There is a slag film between the mold wall and the solidified shell, which plays a lubricating role, reducing the pulling resistance and preventing the solidified shell from sticking to the copper plate.
(5) Filling the gap between the billet shell and the mold, improving the heat transfer of the mold.
A good protective slag should be able to fully exert the above five functions to improve the surface quality of the billet and ensure the smooth progress of continuous casting.
2. What are the requirements for protective slag melting mode?
The protective slag added to the mold during continuous casting must perform the above five functions. The protective slag powder must have a specified melting mode, that is, it is required to form a so-called three-layer structure of powder slag layer-sintered layer-liquid slag layer on the surface of the molten steel.
Low-melting-point (1100～1200℃) slag powder is added to the surface of the high-temperature molten steel (around 1500℃) in the mold. The heat from the molten steel forms a liquid slag covering layer of a certain thickness (about 10～15 mm) on the surface of the molten steel. The heat transfer from the molten steel to the powder slag layer slows down, and the powder slag on the liquid slag layer is heated. The slag powder is sintered together to form a so-called sintered layer (temperature at 900～600℃). The powder slag on the sintered layer receives less heat transferred from the molten steel, and the temperature is low (<500℃), so it remains powdery and evenly covers the surface of the molten steel, preventing heat dissipation of the molten steel and preventing oxygen in the air from entering the molten steel.
During the pulling process, due to the up and down vibration of the mold and the downward movement of the solidified shell, the liquid slag layer on the surface of the molten steel is continuously squeezed into the gap between the billet shell and the copper wall through the interface between the molten steel and the copper wall, forming a solid slag film on the surface of the copper wall. A liquid slag film is formed on the surface of the solidified shell. This liquid slag film plays a lubricating role between the mold wall and the billet surface, just like adding lubricating oil when the motor shaft rotates. At the same time, the slag film fills the gap between the billet shell and the copper wall, reducing the thermal resistance and improving the heat transfer of the crystallization.
As the pulling process proceeds, the liquid slag on the surface of the molten steel is continuously consumed. The sintered layer descends to the surface of the molten steel and melts into a liquid slag layer, and the powder slag layer becomes a sintered layer. New slag powder is added to the mold to maintain the three-layer structure. This cycle continues, and the protective slag powder is continuously consumed.
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