Magnesia carbon brick is still the most widely used steel-making refractory because of its high cost performance. Magnesia carbon brick has great advantages of erosion resistance and spalling resistance, but also has the disadvantages of poor thermal insulation and easy carburizing to ultra-low carbon steel water. With the specialization and subdivision of smelting steel requirements, higher requirements are put forward for refractory materials. Low-carbon and carbon-free refractories can effectively reduce the amount of carbonization of molten steel, reduce the temperature of the ladle shell, and reduce the superheat of molten steel. Improving quality and reducing costs will be the future development of the metallurgical industry.
In order to meet the requirements of customers, in recent years, refractory enterprises have introduced low-carbon magnesia carbon bricks, aluminum magnesium spinel castables, precast blocks and other low-carbon, carbon-free materials, in order to reduce costs, but also the use of the ladle cast process, spray repair process.
This paper mainly introduces the research and application of low-carbon and carbon-free ladle materials.
1. Low carbon magnesia carbon brick
In order to reduce the migration of carbon in low-carbon magnesia carbon bricks to molten steel, the pursuit of carbon content and erosion rate to achieve the lowest, rather than simply the lowest carbon content. Containing 4% to 5% carbon (excluding resin carbon) low carbon magnesia carbon brick (main physical and chemical indicators see table 1) has been used in many domestic steel mills, in actual use of the erosion rate and MT-14A magnesia carbon brick close, there is no obvious spalling phenomenon, the use effect is relatively stable.
Low carbon magnesia carbon brick with magnesia, fine graphite, resin as the main raw material. Considering that low-carbon magnesia-carbon bricks are often used for smelting ultra-low carbon steel, the oxygen content in molten steel is high, and sometimes the alkalinity of steel slag is relatively low, so as to improve its density, so as to enhance its oxidation resistance and corrosion resistance. The developed low-carbon magnesia-carbon brick has an apparent porosity of about 2.5% and a volume density of about 3.17g.cm-3, and its compactness is no less than that of regular magnesia-carbon brick. In some cases, the erosion rate is less than that of regular magnesia-carbon brick with carbon content ≥ 10%. The key to the development of low-carbon magnesia-carbon bricks is to improve their anti-spalling properties. In the process of development, the thermal expansion rate and the elastic modulus at high temperature are controlled. After the developed product is fired at a high temperature of 1600 ℃, the linear change rate is less than or equal to 0.6, and the elastic modulus is less than or equal to 4000MPa under the condition of embedding carbon at 1600 ℃ for 30min. Low carbon magnesia carbon brick in a well-known steel mill 150t refining ladle used 50 times (slag line position), the surface is smooth and flat, and the residual brick without fracture, spalling traces.
2. Carbon-free press brick
According to the characteristics of the original magnesia-carbon brick production line, a carbon-free machine-pressed brick (aluminum-magnesium unfired brick) for refining ladle was developed. The production of carbon-free press bricks can make full use of the original production equipment and process flow of magnesia-carbon bricks, and the production efficiency is high.
Carbon-free press brick with bauxite, corundum, magnesia, aluminum magnesium spinel, alumina powder as the main raw material, with resin or inorganic binder combination. Due to the use of large tonnage press molding, carbon-free press brick is relatively dense.
It is mainly used for ladle melting pool and bottom part, and is consistent with magnesia carbon brick ladle in brick type, masonry and baking.
In the early stage of development, the carbon-free machine pressure brick spalling phenomenon, after many adjustments, the use of basic stability. At present, the ladle lining built with machine-pressed brick can be used 80 times at a time without repair on a 180t refining ladle in a factory, with little spalling and no obvious crack in brick joints.
3, aluminum magnesium pointed stone castable, precast block
Aluminum magnesium spinel castables have been widely studied and applied in China, and it is believed that the cost of corundum-magnesium oxide system is more advantageous, but the comprehensive performance of corundum-spinel system is more stable.
The thermal expansion of products using pre-synthesized spinel in the whole heating process is relatively gentle, slightly expanded after cold, and the change of re-burning line is still slightly expanded, and its volume density and apparent porosity are relatively good. The high temperature thermal flexural strength of the sample using pre-synthesized spinel is better, that is, it has better comprehensive performance at the actual use temperature. The sample using pre-synthesized spinel also has a better performance in the case of resistance to converter slag erosion, reflecting a higher slag resistance.
The castable with white corundum, plate-shaped corundum, pure calcium aluminate cement and spinel as the main raw materials has the characteristics of convenient construction and high service life (equivalent to magnesia carbon brick). The key point is to control the volume stability and the rate of change of the re-burning line, and to balance the peeling resistance and corrosion resistance in the design. Based on the experience of using 120t refining ladle in a steel mill, the erosion rate of this castable is less than 1mm per furnace at the most severely eroded part.
In some steel mills, due to unsatisfactory construction conditions, deformation of the steel cladding, or long-term baking of the ladle, the ladle lining can only be built with aluminum-magnesium precast blocks. Aluminum-magnesium precast blocks are produced by casting molding. Each precast block weighs about 10kg and can be built and baked like magnesia-carbon bricks. It is generally believed that with the decrease of cement content, the permeability resistance of corundum spinel castables is weakened and the corrosion resistance is improved. Aluminum-magnesium precast block is cement-free corundum-magnesium oxide, the actual use of erosion rate is better than low cement aluminum-magnesium castable, but the production efficiency of precast block is relatively low.
4. Ladle Spraying Material
Many companies have done tests on the magnesia carbon brick lining of the ladle, but the actual application is few and the effect is not ideal. It is feasible to spray the lining of aluminum-magnesium castable. The spraying technology of ladle is a good supplement and perfection to aluminum-magnesium ladle castable, which can repair the weak parts that may appear and have appeared in the ladle, and ensure the stability and safety of the ladle during operation. It can directly cover the aluminum-magnesium spray material on the surface of the original castable to form a new working layer and avoid the waste of resources and environmental pollution caused by the removal of the castable. At present, cold spray patching on a 120t refining ladle in a steel plant can achieve the effect of 40 times of spray patching once. This can achieve a new package pouring, pouring, spraying and other means to ensure the use of the effect, control the overall cost.