This article describes the performance and characteristics of continuous casting nozzle slides made of different materials, as well as their application and development.
Key words: slide gate plate; performance; application development
High Aluminum slide gate plate
Before the 1980s, my country’s steelmaking was dominated by open-hearth furnaces, and there were also converters and some electric furnaces. The capacity of the die-casting ladle was small, and the pouring time was short. There was basically no continuous casting and refining outside the furnace.
At this time, the production process of slide gate plates is similar to that of ordinary high-alumina bricks. Bauxite clinker is used as the main raw material, which is fired at high temperature to form a mullite bonded phase, and then dipped in asphalt.
This high-aluminum slide plate met the needs of small ladle die-casting in my country at that time, but it had the following disadvantages:
(1) The corrosion resistance is poor, and the sliding surface and the gate are severely eroded.
(2) The thermal shock stability is poor, and cracks are easy to occur during use.
Aluminum carbon slide gate plate
Carbon materials such as graphite and petroleum coke and antioxidants such as Si and SiC are added to the ingredients of high-alumina slide gate plates, and water glass and phosphate are used as binders. After low-temperature baking and dipping in asphalt, non-burning slide gate plates are produced.To improve erosion resistance and thermal shock stability, synthetic mullite, andalusite and silicon carbide materials are added to the pellets, and corundum and silicon carbide are added to the matrix. In order to increase the strength of the carbon mesh and reduce the porosity, a small amount of asphalt powder was added.Due to the small thermal expansion coefficient and good thermal conductivity of the carbon material, and it is not easy to be wetted by liquid metal and slag, and the combination of resin makes the particles form a carbon network bond, thereby increasing the high temperature strength of the slide. The carbon mesh wraps the particles to form a surface that is difficult to be wetted by the molten material. Compared with the high-aluminum slide, this slide has obvious improvements in erosion resistance and thermal shock.
At present, most of the ladles below 30t in my country generally use this kind of non-burning slide plate. But its disadvantage is that it can only be used once, and the main problems appear in the following two aspects: low thermal strength, serious wear of sliding surface; poor crack resistance.Sintered aluminum carbon slide gate plate is a product developed in the late 1970s. It uses sintered alumina and synthetic mullite as the main raw materials, and partially adds carbon components and antioxidants (such as metal aluminum, metal silicon, SiC, B4C, Mg-B, etc.)Fired in a reducing atmosphere to form a carbon-bonded refractory. The sliding plate of this material has good corrosion resistance due to its dense structure, fine pores, and a certain amount of residual carbon, which is difficult to impregnate with molten steel and slag;
But its disadvantage is that due to the compact structure, the thermal shock resistance is reduced, and it cannot be used continuously for many times. Secondly, during the use process, because the carbon is easily oxidized, the structure is loose and the corrosion resistance is reduced.
In recent years, metal nitride bonded aluminum carbon slides have been developed. The corundum commonly used in the production of slide gate plates is used as the aggregate, the metal aluminum powder is used as the main matrix, and an appropriate amount of catalyst is added to melt and moderately nitride the metal aluminum at a suitable temperature. The final material structure is made of corundum as the skeleton.Metal aluminum forms a continuous film and wraps around the particles. As a reinforcement, AN is evenly dispersed in the metal matrix to form a fine-grained structure. The purpose is first to use the low expansion coefficient and excellent thermal conductivity of AN to improve the thermal shock resistance of the slide;The generated AN micro-particles dispersed in the matrix can hinder dislocation movement and crack propagation, and also have the effect of dispersion toughening, and the molten aluminum at high temperature is in a plastic state, which can fill pores, reduce the brittleness of ceramic materials, give full play to the oxidation resistance of metal aluminum and aluminum nitride and the non-wetting property of aluminum nitride, and improve the ability of the slide to resist the erosion of high calcium and high oxygen steel. It shows its superiority in casting calcium treated steel and high oxygen steel.
Aluminum zirconium carbon slide gate plate
Aluminum carbon sliding plate has quite good performance and applicability, but the cracking and sliding surface wear in repeated use are the key to restricting the improvement of its life.Aluminum-zirconium carbon slides are developed on the basis of fired aluminum-carbon slides. The slide plate made of this material uses Al2O3-SiO2-ZrO2 raw materials with low expansion rate, and is made of baddeleyite, mullite, corundum, etc. as the main crystal phase, and the refractory material is characterized by carbon bonding.
Firstly, zirconia-mullite is introduced as aggregate, and the zirconia in zirconia-mullite undergoes crystal transformation at about 1000°C, which has the characteristics of volume shrinkage and micro-cracks in the grains, which greatly improves the thermal shock resistance of the material. Secondly, ZrO2 has excellent corrosion resistance, and its corrosion resistance is significantly improved compared with aluminum-carbon slide gate plates, and it has become the mainstream in the use of skateboards in large steel enterprises today.In Baosteel, the main raw materials used for aluminum-zirconium-carbon slide gate plates are tabular corundum, zirconium corundum, zirconium mullite, carbon, etc. The binder is phenolic resin with a residual carbon content (mass fraction) greater than 4%, and the additives are metal aluminum, silicon, boron carbide and alumina micropowder.In 2002, the average service life of Baosteel converter ladle slides was 2.5 times, which is relatively low compared with Japan and other advanced countries. At present, some manufacturers use high-purity fused zirconia corundum toughened by TiO2 as raw material, which endows the skateboard with superior performance.
Magnesia carbon and spinel carbon slides
Carbon-bonded aluminum-carbon and aluminum-zirconium-carbon slides are currently commonly used slide materials in steel mills at home and abroad, but these two slides have poor calcium corrosion resistance when casting calcium-treated steel, and are not suitable for casting calcium-treated steel, Al/Si killed steel and other steel types. Magnesium oxide does not react with calcium oxide to form a low-melt product and does not react with ferrous oxide, so magnesium oxide slides are suitable for calcium-treated steel. Magnesium sliding plate was first successfully tested in Europe, because magnesium oxide has good mechanical stress resistance and chemical corrosion resistance, and to a certain extent meets the requirements of cast calcium-treated steel and high-oxygen steel. However, the thermal expansion coefficient of the magnesium oxide sliding plate is large, and it is prone to thermal spalling when pouring steel, so it needs to be improved in terms of thermal shock resistance. At the same time, more and more calcium-treated steels and a large number of high-quality steel castings make the operating conditions more harsh, and magnesium oxide materials are increasingly unsuitable for these harsh operating conditions.
Hepuorth Refractories Company in the United Kingdom improved the magnesia slide plate by replacing the magnesium oxide material with spinel material to improve the thermal shock resistance and wear resistance of the slide plate. However, after actual use, problems such as penetrating cracks, peeling off of the sliding area, falling blocks, and penetration of molten steel also occurred, all of which affected the normal operation and service life of the slide gate plate. Later, on the basis of periclase and spinel slides, magnesia-carbon and spinel-carbon slides were developed, among which the magnesia-carbon slides further improved the disadvantages of poor thermal shock resistance of periclase slides. Under the conditions of high steel pouring temperature, long time, and high oxygen and calcium content in molten steel, magnesia-carbon slides have achieved satisfactory results, but considering their unsatisfactory thermal shock resistance, they are limited to use as slides for tundishes
Spinel carbon sliding plate is a refractory material that uses magnesium-aluminum spinel as the main crystal phase and is characterized by the combination of ceramics and carbon. The thermal expansion coefficient and elastic modulus of magnesium aluminum spinel materials are smaller than that of magnesium oxide, and their thermal shock resistance is stronger than that of magnesium oxide. However, the slow chemical reaction between the spinel material and the calcium in the steel produces low-melting material which affects its service life. Through the improvement of raw materials in the manufacturing process, and the improvement and control of the particle size distribution of the mud and the firing temperature, the erosion resistance of the spinel carbon sliding plate is greatly improved, and the service life is also significantly increased.
Zirconia sliding plate
Zirconia materials have good corrosion resistance (CaO-ZrO2 system equilibrium liquidus temperature above 2000℃) and spalling resistance (low thermal expansion coefficient). The zirconia sliding plate formed by hot pressing has the characteristics of high high temperature strength, low apparent porosity, small pore diameter, etc., and has good corrosion resistance to molten steel when used on the tundish.
MgO partially stabilized zirconia sliding plates with a service life of up to 10 shots under severe casting conditions. Zirconia material has good high temperature performance, but due to its cost and other reasons, the industry generally adopts zirconia zirconium rings inlaid around the casting holes of aluminum carbon slide plates to make composite slide plates. Its base is aluminum carbon, and partly inlaid partly stabilized zirconia zirconium ring is used in the middle. Since the aluminum-carbon matrix is not in direct contact with the molten steel, it avoids the direct erosion of the matrix by the molten steel, and the price of the matrix components is relatively low, accounting for most of the weight of the skateboard; the price of the zirconium ring is relatively high, accounting for a small part of the weight of the slide gate plate. The inlaid slide board uses materials reasonably, not only obtains good use effect, but also reduces production cost. With the increase of calcium treatment of molten steel in our country year by year, the application prospect of mosaicslide gate plate is very broad.