Mold Flux in Continuous Casting Process

1. The main function of the flux

v Stable continuous casting process to ensure that it goes smoothly.

v Improve the surface and subcutaneous quality of the slab.

2. The role of mold flux

In the crystallizer, the protective slag is melted by the heat provided by the molten steel to form a three-layer structure, a slag layer, a sintered layer, and a liquid slag layer.

2.2.1 Insulation and heat preservation in the crystallizer

The thermal insulation effect of the mold flux on the molten steel surface in the crystallizer is mainly achieved by protecting the thickness and physical properties of the particle layer. Main defense the temperature at the molten steel crust and the meniscus in the mold is too low, causing the surface of the slab to be mixed with the skin.

2.2.2 Prevent secondary oxidation of molten steel

The role of the flux in preventing the secondary oxidation of the molten steel in the crystallizer is mainly achieved by protecting the slag liquid slag layer. Usually liquid slag in the mold the layer thickness is in the range of 6-15mm. When the liquid level is stable and the nozzle insertion depth is reasonable, it can play a good role in isolating the air.

2.2.3 Mold flux has the function of absorbing floating inclusions in molten steel

The mold flux should have the ability to absorb the floating inclusions in the molten steel, especially the inclusions at the meniscus in the crystallizer, which should be promptly the slag is assimilated.

2.2.4 Mold flux should have the function of controlling heat transfer

Controlling heat transfer is one of the most important properties of mold flux, which plays an important role in the output of the caster and the surface quality of the cast slab.

2.2.5 Mold flux should have good lubrication

The lubricating property of the mold flux is one of the most important properties of the mold flux. Lubrication refers to the liquid lubrication of the slag film between the shell of the mold and the wall of the mold.

3. Classification of continuous casting mold slag

3.1 Selecting the slag according to the type of cast steel

1) Select the mold flux according to the carbon content of the steel

2) Selecting the mold residue according to the characteristics of the steel

Although it is selected according to the carbon content of the steel, it can not meet the requirements of all steel types. For certain steel grades with special composition, such as high aluminum special protective slag is required for steel, high manganese steel, stainless steel, etc.

3.2 Selecting the mold flux according to the poured section

At present, there are many types of sections cast by continuous casting, such as slabs, billets, round billets, thin slabs and profiled billets, and each type has many sizes of sections, which need to be selected according to each type of section size and casting process.

3.3 Selecting the flux at the blanking speed

Even if the same steel grade and slab section are cast, the difference in the drawing speed of different steel mills is large, and the choice of the slag needs to match the pulling speed.

4. The use of continuous casting mold slag must match the continuous casting process.

4.1 Keep the liquid level in the crystallizer stable. 

The liquid level stabilization in the crystallizer is a prerequisite for ensuring uniform melting of the mold flux in the crystallizer to obtain a uniform liquid slag layer thickness. A high quality slab can only be obtained if a uniform slag film is obtained. When the liquid level fluctuation in the crystallizer is large, not only a large number of defects are generated on the surface of the slab, but also a steel leakage accident occurs, and automatic liquid level control is the most effective measure for ensuring the liquid level stability of the crystallizer.

4.2 The nozzle should be centered. 

If the nozzle is not centered, the crystal liquid will be biased, causing the liquid surface to turn over and the surface of the slab and the skin to be produced a large amount of slag inclusions can cause steel leakage in severe cases. Therefore, the nozzle alignment problem must be fully paid attention to, otherwise it is difficult to obtain a good slab.

4.3 Choose a reasonable nozzle size and insertion depth. 

Choosing a reasonable nozzle size and insertion depth is an important condition for fully utilizing the role of the protective slag. If the depth of the nozzle is too shallow, the liquid level will be unstable. If the turning is too strong, the slag will be caused; if the nozzle is inserted too deeply, it will affect the normal melting of the protective slag and lead to cold steel.

4.4 Avoid using inferior nozzles. 

The inferior nozzle has a low service life, and the frequent water exchange port will cause the liquid level in the crystallizer to fluctuate greatly. Heavy weight will cause defects such as slag inclusion and re-knot in the slab.

4.5 The vibration parameters are adapted to the protective slag. 

In actual production, when selecting the vibration parameters, not only the steel type and the pulling speed but also the role of the protective slag should be considered. In particular, parameters such as amplitude, frequency and negative slip ratio have a great influence on the consumption and lubrication performance of the flux.

4.6 Stabilize the casting speed. 

Pouring at stable casting speed or constant speed, the flow of liquid slag is minimal, and the fluctuations of heat flow and friction are also the smallest. The liquid slag uniformly flows into the gap between the mold wall and the shell in the crystallizer, which can ensure good lubrication and uniform heat transfer of the slab, and avoid cracks to the utmost extent. After the pouring, changing the nozzle and the tundish, the pulling speed should be slowly and steadily increased.

4.7 Avoid punching operations.

The "punching rod" operation will cause the liquid level in the crystallizer to fluctuate greatly, destroying the normality of the mold flux in the crystallizer melting, seriously deteriorating the quality of the slab, sometimes lead to the occurrence of steel leakage accidents. The soft blowing time of the ladle should be ensured as much as possible, the molten steel inclusions should be reduced, and the protection casting should be done to avoid the nozzle clogging. When the quality of the molten steel is poor, it is necessary to appropriately reduce the pulling speed and pass the dangerous period.

4.8 Control the plug to blow argon. 

Reasonable plug argon blowing, in order to maintain the stability of the liquid level in the mold, fully play the role of the protective slag use. Otherwise, the liquid level will fluctuate greatly, forming a large turn, destroying the normal melting of the protective slag, and causing a large number of defects to the slab.

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