Ladle is an indispensable container in the process of steelmaking. With the continuous development of refining technology, especially the processing of LF and RH outside the furnace, its role has developed from the simplest holding of molten steel to a furnace that undertakes a certain smelting function. Molten steel staying in ladle for a long time will inevitably lead to the loss of molten steel temperature, and the high thermal conductivity of the ladle lining will lead to the aggravated heat dissipation of molten steel, the deformation of ladle shell is more serious, the steel water temperature drop rate increases, resulting in serious slag hanging on the ladle wall, nodules and cold steel.
Excessive low temperature, and even forcing the final pouring of the ladle, not only affects the quality of the casting billet, low steel recovery rate, but also increases the production cost. Therefore, thermal insulation ladle is increasingly becoming the demand of steel mills. The structural mode of insulation ladle resistant material is usually light insulation plate or nano plate + permanent layer castable + working layer resistant material.
The insulation board itself needs a layer of refractory material to protect, the material to protect the insulation material from too much pressure, the second to protect the insulation material does not exceed the use temperature (such as must be below 1000 ° C), then the ladle permanent layer castable is this important material. The ideal permanent layer resistant material of thermal insulation ladle should have good thermal stability, thermal insulation, corrosion resistance, safe and reliable application, complete structure, long service life and so on. In order to maintain the good insulation performance of ladle and reduce the drop of steel water temperature, the performance of new CA6 castable and light mullite castable were evaluated respectively in this work and applied to ladle, achieving a better comprehensive insulation effect.
1. Test process
At present, the permanent layer material of ladle is mostly common high aluminum castable, and the main raw material is bauxite. There are the following shortcomings in the use of this refractory castable: first, high thermal conductivity, resulting in energy loss during use; Second, the refractoriness is low, if the use of the working layer is abnormal, when the molten steel directly contacts the permanent layer, the probability of penetration leakage is large, and the safety factor is low; Third, the bulk density is larger, and the empty ladle weight is larger. Therefore, the special requirements for ladle insulation are not met, and a new type of permanent layer castable with excellent comprehensive properties needs to be developed. In this paper, new CA6 castable and light mullite castable are prepared and tested.
1) Raw materials and test plan
CA6 ₃ (CaAl12O19, CA6) is the calcium aluminate phase with the highest content in CaO-Al₂O₃ system. Its melting point is 1875℃, coefficient of thermal expansion is 8.0×10-6℃⁻¹, the bulk density of particles is 2.70g·cm⁻³, and the apparent porosity is 26.8%. The refractory property of the material is similar to that of plate corundum, and the thermal conductivity is only 1/3 of that of corundum. It is a new kind of high-quality thermal insulation raw material that has emerged in recent years. CA6 castable is made of CA6 as aggregate, and the matrix is made of plate corundum powder, aluminum oxide powder and calcium aluminate cement as binder. The bulk density of spherical light mullite particles is 1.59g·cm⁻³, and the apparent porosity is 38.9%. Light mullite castable is made of microporous M70 spherical light mullite ball as aggregate, and the matrix part is made of plate corundum fine powder, aluminum oxide powder and calcium aluminate cement as bonds to ensure better slag erosion resistance and improve the safety of the permanent layer.