What is the function of continuous casting slag?
Release time:
2021-12-17
1. Continuous casting slag What is its function?
During casting, powdery or granular slag materials are continuously added to the surface of the molten steel in the mold, which is called continuous casting slag. Continuous casting slag has the following functions:
(1) Heat insulation and heat dissipation prevention;
(2) Isolating air to prevent oxygen in the air from entering the molten steel for secondary oxidation, affecting the quality of the steel;
(3) Absorbing and dissolving inclusions floating from the molten steel to the steel-slag interface to purify the molten steel;
(4) There is a layer of slag film lubrication between the mold wall and the solidified shell, which can reduce the drawing resistance and prevent 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 continuous casting slag should fully exert the above five functions, thereby improving the surface quality of the slab and ensuring the smooth progress of continuous casting.
2. What are the requirements for the melting mode of continuous casting slag?
In order to complete the above five functions, the protective slag added to the mold during continuous casting must have a specified melting method, that is, a three-layer structure of a powder slag layer, a sintered layer, and a liquid slag layer is formed on the surface of the steel.
Low-melting-point (1100 ~ 1200℃) slag powder is added to the surface of the high-temperature molten steel (approximately 1500℃) in the mold, forming a slag coating of a certain thickness (approximately 10 ~ 15 mm) on the surface of the molten steel. The heat transfer from the molten steel to the slag layer is slowed down, and the slag on the slag layer is heated, and the slag powder is sintered together to form a so-called sintered layer (temperature between 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 the molten steel from dissipating heat and preventing oxygen in the air from entering the molten steel.
During the drawing 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 between the 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 and a liquid slag film on the surface of the solidified shell, which plays a lubricating role on the mold wall and the shell 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 mold heat transfer.
As the drawing proceeds, the liquid slag on the steel surface is continuously consumed, while the sintered layer falls to the steel surface and melts into a liquid slag layer, and the powder slag layer becomes a sintered layer. Then, new slag powder is added to the mold to maintain the three-layer structure, and the continuous casting slag powder is continuously consumed in this cycle.
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