Ladle is an indispensable container in the steelmaking process.
With the continuous development of smelting technology, especially the treatment of LF and RH outside the furnace, its role has developed from the simplest holding molten steel to a furnace that undertakes certain smelting functions. The long-term stay of the molten steel in the ladle will inevitably cause the loss of the molten steel temperature, and the high thermal conductivity of the lining will lead to increased heat dissipation loss of the molten steel, more serious deformation of the ladle shell, and increased temperature drop rate of the molten steel, resulting in serious slag hanging on the wall of the ladle. Nodules, cold steel. Excessive low temperature, even forcing the tundish to stop the final pouring, not only affects the quality of the slab, but also lowers the yield of molten steel and increases the production cost. Therefore, the thermal insulation ladle has increasingly become the demand of steel mills. The structural mode of thermal insulation ladle refractory is usually light insulation board or nano-board + permanent layer castable + working layer refractory.
The most thermal insulation board itself needs a layer of refractory material to protect it. This material should protect the insulation material from too much pressure, and secondly, it should protect the insulation material from exceeding the operating temperature (if it must be below 1000 ℃), then the ladle Permanent layer castables are such important materials. The ideal permanent layer refractory material for thermal insulation ladle should have good thermal stability, thermal insulation, corrosion resistance, safe and reliable application, complete structure and long service life. In order to maintain the good thermal insulation performance of the ladle and reduce the temperature drop of the molten steel, the performance evaluation of the new CA6 castable and light mullite castable was carried out in this work, and applied to the ladle to achieve a better comprehensive thermal insulation effect.
At present, the material of the permanent layer of the ladle is mostly ordinary high-alumina castable, and the main raw material is bauxite. The following shortcomings exist in the use of this refractory castable: first, the thermal conductivity is high, which causes energy loss during use; second, the refractoriness is low, if the working layer is abnormally used, the molten steel directly contacts the permanent layer When , the probability of piercing and leaking steel is high, and the safety factor is low; third, the bulk density is large, and the weight of the empty ladle is large. Therefore, the special requirements for ladle insulation are not satisfied, and a new type of permanent layer castable with excellent comprehensive properties needs to be developed. In this paper, the sample preparation and testing of the new CA6 castable and light mullite castable were carried out.
1. Raw materials and test plan
Among them, the CA6 raw material (CaAl12O19, abbreviated as CA6) is the calcium aluminate phase with the highest content of Al₂O₃ in the CaO-Al₂O₃ system. Its melting point is 1875°C, the thermal expansion coefficient is 8.0×10-6°C⁻¹, and the bulk density of the particles is 2.70g· cm⁻³, the apparent porosity is 26.8%. The refractory performance of this material is similar to that of tabular corundum, and the thermal conductivity is only 1/3 of that of corundum. It is a new type of high-quality thermal insulation material that has emerged in recent years. CA6 castable is made of CA6 as aggregate, and the matrix part is made of tabular corundum fine powder, alumina 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%. The light mullite castable is made of microporous M70 spherical light mullite balls as aggregate, and the matrix part is made of tabular corundum fine powder, alumina powder and calcium aluminate cement to ensure Better resistance to slag erosion to improve the safety of the permanent layer.
2. Test process and performance testing
The physical properties test and corrosion resistance test were carried out for the two kinds of castables after casting. The physical test methods are carried out according to the national standard or industry standard method.
Material Properties Results and Analysis
(1) Physical properties
The bulk density of the lightweight mullite castable is 2.17g·cm⁻³, the unit weight is 24% lower than that of the currently used high-aluminum castable, and the thermal conductivity is reduced by 16%, which can achieve the purpose of lightweight and low thermal conductivity of the ladle . CA6 castables are also 5.6% lighter and 26% lower in thermal conductivity than ordinary high-aluminum castables.
Erosion resistance test
The original ladle permanent layer castable B, the new CA6 castable C, and the light mullite castable 3# were poured into crucibles respectively. The final slag of the converter was added, and the corrosion resistance test of the crucible under the condition of 1500 ℃ heat preservation for 3h was carried out. Observe the melting loss and penetration of different materials. After the test is completed, the crucible is cut open,
The CA6 castable has good erosion resistance and penetration, and a large amount of slag remains in the crucible hole; the light mullite castable has the next highest erosion resistance and resistance to penetration; the boundary between the ordinary high-alumina permanent layer castable slag and the refractory is not clear, and the crucible refractory and the refractory are not clear. The slag is melted together, and the penetration resistance is slightly better than the erosion resistance, indicating that there are more liquid phases in the high-alumina castable at 1500 °C, so the material needs to be improved to improve its high temperature resistance, which is very important for the safety of the ladle. The microporosity of the spherical light mullite is beneficial to the improvement of corrosion resistance and permeability, so the light material can also show better thermal insulation and corrosion resistance.
Application
The above three kinds of castables are applied on the 300t ladle. The light mullite castables and CA6 castables for the permanent layer of the thermal insulation ladle are required to have both good resistance to molten steel erosion and thermal insulation, and at the same time, the structural integrity of the furnace service process is good, and the thermal insulation effect is stable.
The comprehensive technology of how to reduce the cracking of the permanent layer material of the thermal insulation ladle still needs to be further studied.
From the average temperature of each slag line in each ladle, the steel shell of the uninsulated ladle slag line is above 320 °C, while the average temperature of the 4 thermally insulated slag lines is below 280 °C. Generally, the temperature of the slag line steel shell decreases. 50～100℃. The temperature drop of the steel shell at the cladding part is between 20 and 50 °C, which is slightly different depending on the configuration of the thermal insulation material and the permanent layer material. The thermal insulation material of the thermal insulation test bag remained in good condition during the furnace service period, and the average temperature of the slag line and the cladding steel shell was lower than that of the ordinary ladle, indicating that the permanent layer played a good protective role. In order to ensure safety, the current situation where the cracks of the new permanent layer material are more obvious after 2 furnaces still needs to be optimized and improved to ensure that it can be applied to 4 furnaces.
in conclusion
The thermal insulation ladle has become an important technical measure for iron and steel enterprises to save energy and protect the environment and improve the quality of steel products. The material of the permanent layer of the ladle is given higher requirements. The physical properties of the developed CA6 castable and light mullite castable meet the application requirements of the permanent layer of the ladle, and at the same time have better thermal insulation and corrosion resistance than the conventional high-alumina castable, which can protect the thermal insulation material. The role of the ladle to maintain good thermal insulation during the furnace service period. Further in-depth research is needed on the comprehensive technology to reduce the cracking of the permanent layer material of the thermal insulation ladle.
