This paper summarizes the types of dry materials, the research progress of the application of binders, additives and recycled materials in dry materials, and looks forward to the direction and prospects of future dry material research.
Keywords: tundish; dry vibrating material; binder; additive; recycled material
The continuous casting tundish is one of the key devices in the steel continuous casting process. It not only receives the molten steel from the ladle and injects it into the crystallizer continuously, evenly and stably, adjusts the molten steel flow and removes non-metallic inclusions, cleans the molten steel, etc. It also plays a role in refining molten steel. The working lining of the tundish has roughly gone through four development stages: no working lining → insulation board → coating → dry vibrating material (hereinafter referred to as dry material). Its service life is crucial to the service life of the tundish. With the optimization of the continuous casting process and the improvement of the quality requirements for continuous casting billets, higher requirements have been put forward for the cleanliness and longevity of the tundish working lining.
The tundish working lining is in direct contact with molten steel during use and needs to have the following basic requirements: easy construction and baking, easy to turn over after use without damaging the permanent layer; high refractoriness and high-temperature strength, and good high-temperature chemical stability properties, does not pollute molten steel or cause secondary oxidation of molten steel; excellent thermal shock resistance and volume stability; good resistance to slag corrosion and penetration; good thermal insulation performance, etc. As the fourth generation tundish working lining, in addition to the above characteristics, dry materials also have the advantages of simple equipment, low labor intensity, short baking time, fast tundish turnover, long service life and energy saving and consumption reduction. It is now available in It has been widely used in major steel plants.
In recent years, more and more research has been done on dry materials, and some results have been achieved. The following introduces the types of dry materials, binders, additives and research progress in the application of recycled materials in dry materials.
Types of dry ingredients
Tundish dry materials can be divided into magnesium, magnesia-calcium, magnesium oxide-forsterite, silicon and magnesium carbon based on different materials.
Magnesium Dry Ingredients
Magnesia dry material is a tundish dry material prepared with fused magnesia or sintered magnesia as the main raw material, supplemented by various binders.
Li Fang et al. compared the physical properties of inorganic salt-bound magnesia dry materials using fused magnesia and mid-grade sintered magnesia as the main raw materials after heat treatment at different temperatures, and found that the dry materials using fused magnesia as the raw material have better The physical properties are better. He Guozhu et al. found that particle gradation will affect the volume density of magnesia dry materials: when the addition of continuous particles is too concentrated, it is not conducive to improving the volume density of dry materials; while when the addition of continuous particles is spaced, it is conducive to improving the dry material. The volume density of the material.
Magnesium Calcium Dry Ingredients
Magnesia-calcium dry material is a tundish dry material made from magnesia-calcium sand as the main raw material, or magnesia as raw material, adding CaO source, and then supplemented by various binding agents. The free CaO contained in magnesium-calcium dry materials can react with oxide inclusions and [S], [P] in steel to improve the cleanliness of molten steel and has strong resistance to slag erosion. The sources of CaO in magnesium-calcium dry materials include magnesia-calcium sand, limestone, slaked lime, magnesium dolomite, etc. In recent years, there have been many studies on the introduction form of CaO in magnesium-calcium dry materials.
Li Yousheng et al. found that when the CaO source is introduced in the form of anhydrous active limestone, the limestone decomposes at high temperatures, and part of it exists in the form of free CaO; the other part reacts to form the low melting point phase calcium forsterite (CMS) and dicalcium silicate. (C2S), and C2S undergoes a β→γ phase transition during the cooling process of the dry material, generating a γ-C2S phase, causing volume effects and causing structural defects in the dry material. Therefore, as the amount of limestone added increases, the residual CaO and the generated γ-C2S phase in the dry material will increase, causing the compressive strength of the dry material to significantly decrease and the disintegration performance of the dry material to gradually improve.
Research by Cheng Peng et al. also found that magnesia-calcium dry materials added with some limestone particles have better overall properties; limestone fine powder is helpful to increase the strength of dry materials after heat treatment and improve the disintegration performance of dry materials; and Dolomite particles and slaked lime fine powder have obvious adverse effects on the post-burning linear change rate and low-temperature bonding strength of dry materials, and are not suitable as CaO source materials for dry materials.
However, Wang Bingjun and others successfully developed a dry tundish material with excellent corrosion resistance and good disintegration properties using sintered magnesia sand, magnesite and dolomite as the main raw materials. In the literature, an environmentally friendly tundish dry material with excellent performance was successfully developed using magnesite and limestone as aggregates and magnesite and slaked lime as fine powder. The author believes that if the appropriate low-temperature and medium-temperature type binders and addition amounts can be selected to eliminate or suppress the adverse effects of adding hydrated lime and dolomite on dry materials, then hydrated lime and dolomite can be introduced into the magnesia-calcium dry material as CaO sources. It is feasible in the formula material.
Magnesium oxide-forsterite dry material
As a high-quality refractory raw material, forsterite (M2S) has high melting point, low thermal conductivity, good thermal insulation performance, high refractoriness, no need for calcination before use, good chemical stability, and resistance to the erosion of molten metal and slag. Excellent, good compatibility with most alkaline refractory raw materials. Compared with magnesia, forsterite is cheaper, rich in resources and widely distributed. Using it to replace part of magnesia can further reduce production costs, save natural resources, save energy, reduce emissions and protect the environment while meeting usage requirements.
Research by Li Fang and others found that adding part of forsterite raw material as aggregate to dry materials has better physical properties at room temperature than clinker as aggregate. The appropriate addition amount of forsterite raw material is about 15% (w). The affinity between forsterite clinker and magnesia fine powder is poor, resulting in low physical properties of dry materials added with forsterite clinker at room temperature. Chen Yong et al. found that there is little difference between adding raw forsterite and adding light-burned forsterite to the dry magnesia-forsterite material on the physical properties of the sample at room temperature; when raw forsterite or light-burned magnesium When the amount of olivine added is controlled to not exceed 45% (w), the slag resistance performance of the sample changes little with the increase in the amount of raw forsterite or light-burned forsterite.
Ma Qinghua and others used forsterite and magnesia as the main raw materials, and special-grade alumina, phenolic resin, glucose, sodium tripolyphosphate, silicon powder, etc. as binding agents to make magnesium oxide-forsterite dry materials, and found that they are used During the process, high-temperature phases with better performance will be formed in different parts. In both the medium-temperature loose layer and the high-temperature sintered layer, the MgO-2MgO·SiO2 refractory material is reacted. The medium-temperature loose layer uses M2S as the main phase, and cordierite with a smaller expansion coefficient is the secondary phase; the high-temperature sintered layer uses M2S as the main phase. , a certain amount of magnesium ferrite and a small amount of magnesium aluminum spinel (MA) are secondary phases. On the inner surface in contact with molten steel, the dry material absorbs Al2O3 in the molten steel to form a MA adhesion layer with better performance. These high-temperature phases, M2S and MA, give the dry material excellent resistance to molten steel erosion and penetration, good heat insulation performance and a long service life.
Wu Shengli used forsterite particles and fused magnesite as the main raw materials, used steelmaking waste secondary resources containing 15%~20% (w) Cr2O3 as the modifier, and used inorganic environmentally friendly SN type binders to successfully develop Magnesium oxide-forsterite dry material with excellent performance and an average service life of more than 14 hours (more than 20 heats). Li Jie et al. used magnesia and forsterite sand as aggregates and fine powder, a combination of bakelite, aluminum dihydrogen phosphate, caustic soda, and polyvinyl chloride as binding agents, and organic curing agents (lactone, carbonate, A combination of ethylene glycol diacetate), slaked lime, etc. was used as additives, and aluminum oxide powder, silica powder and magnesium oxide powder were added to create a self-hardening tundish dry material, which can be left at room temperature for 0.5 to 5 hours. It can be demolded immediately and can be used online without baking.
Silica dry material
Siliceous dry material is a kind of tundish dry material which is mainly made of siliceous raw materials. Its bulk density is much lower than that of traditional magnesium dry materials, and it has better thermal insulation performance, which can significantly reduce heat loss and enable lower baking temperatures. However, there are few studies and applications of this type of dry materials.
Cao Taoyuan uses silica particles, fine powder, and micro powder as the main raw materials, resin powder as the low-temperature binding agent, and clay as the burning accelerator. The residual carbon after high temperature of the resin is used to form a residual carbon network structure, and the silica powder reacts with the clay to form a ceramic sintered layer to increase the strength of the working lining structure, improve the corrosion resistance and erosion resistance, and successfully develop an energy-saving, environmentally friendly, and low-cost silica Dry ingredients.
Research on binding agents
Binder is one of the most important raw materials that affects the performance of dry materials. It needs to meet the following basic requirements: not easy to absorb moisture, easy to store, not producing harmful gases during baking and use, not polluting molten steel, and having high strength. , not over-sintered with the permanent layer, easy to turn over, etc.
The binders of dry materials can be divided into two types: low-temperature binders and medium-temperature binders. Substances that enable dry materials to bond below 300°C are called low-temperature binders, and substances that enable dry materials to sinter at 300~1100°C and increase their strength are called medium-temperature binders.
Low temperature bonding agent
Resin binder
The most widely used low-temperature binder is phenolic resin powder. After low-temperature heat treatment, the resin powder can form a strong three-dimensional grid structure, which can give the dry material higher bonding strength. The dry materials combined with it are easy to construct, easy to turn over, have good disassembly performance and long service life, so they have good use effects in the tundish smelting process.
Wu Wuhua and others found that as the amount of phenolic resin increases, the compressive strength of dry materials first increases and then decreases after baking at 250°C and medium temperature treatment at 1100°C, reaching a maximum value at 4% (w). Research by Wei Juncong and others found that when the amount of phenolic resin binder in magnesia dry materials is more than 5% (w), it can ensure that the dry materials can be safely demoulded after baking, or used directly after demoulding. Gao Hongyue et al. found that it is more appropriate to add 2% (w) phenolic resin powder to magnesia-calcium dry materials.
However, dry materials bonded with resin powder have some shortcomings. First, irritating gases such as formaldehyde and phenol are produced during the baking process, which pollutes the environment. Second, dry materials bonded with resin will release CO2, For gases such as CO, CH4, H2 and H2O, the network structure is destroyed, the medium and high temperature strength of the dry material is reduced, and the molten steel will be significantly carbonized and hydrogenated; thirdly, the price of phenolic resin powder is relatively high, and the dry material combined with it will The production cost of type materials is higher. For this reason, some researchers have modified phenolic resin in order to obtain better performance and reduce costs.
When Tang Yilin et al. synthesized phenolic resin from phenol and aldehyde, they added low-temperature binding substances (one or more of asphalt, sucrose, paraffin, and rosin) and medium-temperature binding substances (sodium tripolyphosphate, sodium silicate nonahydrate, magnesium chloride hexahydrate , boric acid, borax decahydrate and borate glass (one or more), lignosulfonate substances and curing agent (hexamethylenetetramine), to prepare a modified phenolic resin binder for dry materials. In addition, Tang Yilin and others used rosin resin waste, coumaron resin waste or epoxy resin waste to modify phenolic resin, and produced a modified phenolic resin with a carbon residual rate of 20% to 30% (w). The dry materials using these two modified phenolic resins as binders respectively reduce the release of harmful gases during subsequent baking and use, reduce the carbonization of molten steel, and reduce costs. At the same time, they can be burned at low, medium and high temperatures. The final strength was improved.
Environmentally friendly binder
Dry materials added with environmentally friendly binders will not produce harmful smoke during baking and use, and will not harm the environment or the health of workers. Environmentally friendly binders are generally divided into two types: organic binders and inorganic binders. Organic binding agents include sugar substances, such as maltose, glucose, xylose, galactose, fructose, polyhydroxy sugars, polyethylene and rosin; inorganic binding agents include sodium metasilicate, hydrated sodium silicate, silica micropowder, bentonite and Clay etc.
Li Fang et al. compared five environmentally friendly binders, Na2SiO3·5H2O, Na2SiO3·9H2O, MgSO4·7H2O, Mg(NO3)2·6H2O and MgCl2·6H2O, and found that when equal amounts of binders were added, those combined with Na2SiO3·9H2O Magnesium dry materials have the highest normal temperature compressive strength, and the appropriate addition amount is 5% (w); while dry materials combined with MgSO4·7H2O contain sulfur, which has the problem of “increasing sulfur” to molten steel; The dry materials with Mg(NO3)2·6H2O and MgCl2·6H2O as binders respectively will emit pungent odor gas during the mixing and baking process, and the dry materials with Mg(NO3)2·6H2O The material strength is the lowest.
Gu Huazhi et al. believe that as the heat treatment temperature increases, the bonding mode of metasilicate-bonded dry materials changes from adhesive bonding to chemical bonding, and then to ceramic bonding. Metasilicate melts during low-temperature heat treatment, adsorbs on the surface of the material, bonds the material together, decomposes and dehydrates, and reacts with MgO to form some M-S-H compounds; as the temperature rises, the M-S-H compounds decompose and further release crystal water; the temperature continues When the temperature rises, the binding agent and MgO generate a sodium-containing low melting point substance (Na2O·MgO·SiO2) to promote the sintering of dry materials.
The literature uses silica powder, rosin and bentonite as low-temperature binding agents in magnesium dry materials, adds aluminum hydroxide powder, and uses the water vapor generated by the decomposition of aluminum hydroxide powder during the baking process to moisten the internal particles of the dry materials. The surface of magnesia and silica powder are hydrated, and the two form a magnesium-silica gel combination. At the same time, the water generated by decomposition makes the bentonite viscous and plays an auxiliary bonding role, thus improving the drying strength of the dry material. Jia Jiangyi et al. used soft clay and silica powder as a composite low-temperature bonding agent, and used the free water generated by the decomposition of the clay at 420°C to combine with the silica powder in the matrix to form -Si-OH groups, which improved the post-baking strength of the dry material. .
Zheng Yu et al. compared the effects of two polyhydroxy sugars (white sugar and glucose) on the performance of magnesium-calcium dry materials. The study found that the binding capacity of these two polyhydroxy sugars at a low temperature of 150°C is relatively large, and the dry material combined with them has high strength after baking and can meet the requirements of use; it was also found that the dry material using white sugar has better The linear change rate after mild high-temperature burning is generally smaller than that using glucose. Wei et al. compared the thermogravimetric and differential thermal analyzes of three types of polyhydroxy sugars and resin powders, and selected polyhydroxy sugar B with a water loss temperature of 100°C, a melting temperature of 160°C, and a decomposition temperature range of 200~400°C. Using low-temperature binders, an environmentally friendly magnesium dry material was developed and successfully used in many steel plants.
Cheng Peng et al. found that comparing environmentally friendly binders and phenolic resin binders, their binding properties are: polyhydroxy sugar 4% (w) + hydrated sodium silicate 8% (w) > phenolic resin 4% (w) )> Rosin 5% (w)> Polyhydroxy sugar 4% (w)> Polyhydroxy sugar 4% (w) + citric acid 2% (w).
Composite binder
Phenolic resin powder and environmentally friendly binders each have their own advantages and disadvantages. Combining the two to form a composite binder can improve the overall performance of dry materials.
Research by Huang Bo and others found that when glucose, rosin, sucrose and phenolic resin are used in combination, sucrose has the most severe mold sticking, and glucose and phenolic resin powder have the highest intensity when mixed with it. When glucose replaces most of the phenolic resin powder, the bending resistance after baking at 190°C The strength can be retained by more than 70%, the cost can be reduced, and the environmental friendliness is enhanced. The appropriate addition amount is 5% (w).
Qiao Le et al. added phenolic resin, Na2SiO3, Na2SiO3·5H2O, Na2SiO3·7H2O, Na2SiO3·9H2O and other binding agents into the magnesium tundish dry material, and found that 4.5% (w) Na2SiO3 · 9H2O + 0.5% (w) resin powder As a composite binder, the physical properties of the dry material are better than those using the same amount of Na2SiO3·5H2O and Na2SiO3·7H2O as binders; using 4% (w) Na2SiO3·9H2O + 0.5% (w) resin powder The dry material prepared by composite has the best physical properties and slag resistance at room temperature; and the composite binder of 3% (w) resin powder + 2% (w) Na2SiO3 can meet the requirements of on-site construction and reduce the cost of dry material. Cost of production.
Medium temperature binder
The medium-temperature bonding agent, also known as the burning aid, is used to ensure that the dry tundish material has a certain strength after baking at a medium temperature (around 1100°C) before pouring steel, and can withstand the impact of molten steel without causing the working lining to collapse. Commonly used medium-temperature binding agents include boric acid, borax, borate, boron glass, phosphate (sodium tripolyphosphate, sodium hexametaphosphate), silicate, sodium fluoride, etc. Some studies have found that the appropriate amount of medium-temperature binding agent should be controlled at 1.0% ~ 1.5% (w).
Gao Hongyue et al. respectively studied the effect of the addition of medium-temperature binder sodium hexametaphosphate and solid water glass on the performance of magnesia-calcium tundish dry materials using phenolic resin powder as low-temperature binder. It is found that the addition of sodium hexametaphosphate is beneficial to increasing the medium and high temperature strength of dry materials. However, when the addition amount is higher or lower than 0.5% (w), the low melting matter generated will affect sintering. The appropriate addition amount is 0.5%(w). On the one hand, the addition of water glass will generate low-melting point alkali metal substances in the dry material; on the other hand, it will also promote the generation of high-melting point substances such as C2S, tricalcium silicate (C3S), M2S, etc., making the dry material more durable at high temperatures. It is easy to sinter; however, if the addition amount is too large, there will be too many low-melting point substances in the dry material, which will inhibit sintering. The appropriate addition amount is about 0.5% (w).
Zheng Yu et al. found that the addition of sodium tripolyphosphate, a medium-temperature binder, is beneficial to increasing the medium- and high-temperature strength of magnesia-calcium tundish dry materials using phenolic resin powder as low-temperature binder. However, when the addition amount is inappropriate, its The decomposition of excessive low melting point substances will affect solid phase sintering, and the appropriate addition amount is 1% (w).
Li Yousheng et al. believe that boric acid, borax and borate glass have better medium-temperature bonding properties than sodium tripolyphosphate and magnesium chloride hexahydrate, and can significantly promote high-temperature sintering of magnesia materials; however, borax discharges crystal water due to heating. The surface of dry material samples is prone to powdering and is not suitable for use. Wu Wuhua et al. found that when the addition amounts (w) of borax, sodium fluoride, and sodium hexametaphosphate are 1.5% and 1% respectively, they have a very obvious sintering-promoting effect on magnesium dry materials baked at medium temperature, and their The order of the burning-promoting effect from strong to weak is: borax>sodium fluoride>sodium hexametaphosphate. Some studies have also found that the effect of medium-temperature binding agents is as follows: water glass > sodium hexametaphosphate > sodium tripolyphosphate. Among them, sodium hexametaphosphate is more suitable as a medium-temperature binding agent.
Research on additives
Toughening agent
The addition of toughening agents can improve the high-temperature properties of tundish dry materials, such as thermal shock resistance. Some studies have pointed out that when zirconia is added as an additive to magnesia-calcium dry materials, it will react with CaO to generate CaZrO3. At the same time, ZrO2 and MgO form a solid solution at high temperatures; due to the small amount of ZrO2 added and the different electricity prices of Ca2+ and Zr4+, During the reaction process, cation vacancies can be generated in the CaO crystal, thereby effectively promoting sintering. When Gao Hongyue et al. studied the effect of the addition of zirconia on the performance of magnesium-calcium dry materials, they found that the addition of 1% to 1.5% (w) ZrO2 can increase the normal temperature and high-temperature post-fired strength and volume of magnesium-calcium dry materials. Density and resistance to slag erosion. The original Zr4+ in the eroded layer dissolves outward into the intermediate slag, while the ZrO2 and CaO in the uneroded layer react to generate CaZrO3, which promotes the growth of periclase crystals and improves the high-temperature performance of the material.
After adding zirconium micropowder to the dry material, the thermal shock resistance of the dry material can be significantly improved by utilizing the toughening effect of ZrO2. Jiang Qunying et al. used magnesia and magnesia-calcium sand as raw materials, anhydrous glucose and borax as low-temperature and medium-temperature binding agents respectively, and added 4% to 4.5% (w) zirconium micropowder to successfully develop a product with good resistance to molten steel. Steel slag performance and thermal shock resistance, environmental protection, high efficiency and long service life of zirconia toughened magnesium calcium dry material.
Anti-slag erosion penetrant
As the cost of magnesia raw materials increases and companies pursue the reduction of dry material costs, low-grade magnesia raw materials are used in large quantities. The smelting process is also changing, causing magnesia dry materials to suffer from serious sintering and poor slag penetration resistance during use, resulting in reduced service life of dry materials, difficulty in turning over the package after use, and prolonging the construction period. How to improve the anti-slag erosion and penetration performance of dry materials has been studied and reported by a large number of researchers.
When Qian Yuejin et al. studied the erosion mechanism of slag on the dry materials of the tundish, they found that in the early use of the tundish, the way the slag corrodes the working lining of the tundish is through penetration; while permeating, the slag chemically corrodes the dry materials. And the dry material has a chemical filtering effect on the slag. The dissolution of periclase in the slag changes the properties of the slag, increases the melting point and viscosity of the slag, and forms a dense structure at the dry vibrating material-slag interface to hinder Further penetration of slag. After that, the main way that the slag erodes the dry material is through the dissolution of the dense layer at the interface.
Li Fang et al. found that the dry material combined with Na2SiO3·9H2O has better slag resistance than that combined with phenolic resin; the slag corrosion process is mainly based on penetration. During the penetration process, periclase reacts with the molten slag to generate C3MS2, MA and CMS, increase the viscosity of the slag, form viscous bonds between periclase particles, and slow down the further penetration of the slag; at the same time, the expansion accompanying the formation of MA can fill the pores in the sample, thus benefiting the material The structure is densified and its slag resistance is improved.
Cheng Peng and others found that about 9% (w) high-alumina bauxite powder or about 4% (w) “-Al2O3 powder is added to the magnesia dry material, and it reacts with magnesia to form magnesia-aluminum tips. Crystals, filling the pores between particles, can effectively improve the resistance to slag erosion and penetration of magnesia dry materials. The literature also reached a similar conclusion. Liu Deren added light-burned MgO powder and “-Al2O3 micro powder to the matrix, and the same The spinelization reaction is used to improve the corrosion resistance of dry materials. There is also research on simultaneously introducing 9% (w) special grade alumina powder and 2% (w) pre-synthesized spinel powder into the matrix of magnesia dry material to achieve the purpose of improving slag resistance permeability. Nie Hongbo believes that with the same addition amount, synthetic raw materials containing Al2O3 have better slag permeability resistance than natural raw materials containing Cr2O3.
Research by Gao Hongyue and others found that when 2% to 3% (w) Fe2O3 powder (iron red) is introduced into the magnesium-calcium dry material with w (CaO) = 23% magnesia-calcium sand as the main raw material, the added Fe2O3 A small part of the powder is solidly dissolved in periclase grains, and most of it reacts with CaO in the matrix to generate low melting point dicalcium ferrite (C2F) and ferroaluminate compounds, which promote the sintering of magnesia-calcium dry materials and improve dryness. The strength and density of the dry material are increased, thereby enhancing the resistance to slag erosion of the dry material.
Wang Lin et al. added four carbonaceous materials (particle size = 0.15mm) to magnesia dry materials according to w (C) = 3%, including metallurgical coke powder, waste electrodes, crushed petroleum coke and flake graphite, and found that: After introducing these four carbonaceous materials into the magnesia dry material, the partial carbon oxidation in the sample will generate CO gas, which will increase the air pressure inside the dry material sample and prevent the slag liquid from penetrating; the slag liquid will only interact with the surface. The magnesia layer reacts to form a thinner (sintered) metamorphic layer, which significantly improves the slag permeability resistance of dry materials. Among the four types of carbonaceous materials, waste electrodes have the best resistance to slag permeability due to their high fixed carbon content, low ash content, high density and good oxidation resistance.
Li Yousheng et al. found that adding dolomite can improve the slag resistance of magnesia dry materials; adding quartz can reduce the penetration of slag into magnesia dry materials, but the erosion will increase; and adding white corundum cannot improve the magnesia dry materials. The anti-slag performance of the material.
Research on the application of recycled materials
Utilization of waste magnesia carbon bricks
Zheng Kai et al. used waste magnesia carbon bricks after ladle use as aggregate to replace magnesia particles. Using magnesia fine powder as the matrix, phenolic resin powder and boric acid as the binding agent, they developed a product with excellent erosion resistance and corrosion resistance. Magnesium carbonaceous dry material; realizing the reuse of waste materials, greatly reducing production costs and improving production safety. Yu Qifang and others used waste magnesia carbon bricks as aggregate and matrix, modified resin and borax as binding agents, and also successfully developed a product with energy saving, emission reduction, environmental protection, low cost, high normal temperature strength and good high temperature slag resistance. Magnesium carbon dry material. Han Bingqiang and others also successfully developed a magnesium carbonaceous material for tundish lining using waste magnesia carbon bricks as aggregate, magnesia fine powder as matrix, sugar and its derivatives and hydrated sodium silicate as composite binders. Dry material; it has the characteristics of high continuous pouring rate, excellent use effect and easy disintegration after use.
Research by Yuan Tianyi and others found that the overall performance of adding shaped waste magnesia carbon brick particles to magnesia dry materials is better than adding unshaped waste magnesia carbon brick particles. However, when adding these two types of waste magnesia carbon bricks respectively, the addition amount should not be too large, because the graphite in them will hinder the sintering of dry materials and reduce the strength of dry materials after high-temperature firing. The appropriate addition amount is: the amount of unshaped particles does not exceed 15% (w), and the amount of shaped particles does not exceed 30% (w).
Utilization of waste magnesia chrome bricks
The Cr3+ in the used magnesia-chrome bricks has been partially converted into Cr6+, while the Cr6+ in the waste magnesia-chrome bricks is toxic and soluble in water and is lost. If it is directly discharged into the environment without treatment, it will cause harm to the environment and human body. Very harmful. The magnesia-chromium brick itself has excellent slag resistance and is not easy to sinter, and has high recycling value.
Qingguanghong and others added part of the recycled waste magnesia chromium brick powder from the RH furnace into the magnesia dry material to improve the high-temperature corrosion resistance. The slag erosion thickness was reduced from the original 20~30mm to 15~20mm, with an average reduction of 8mm. . Zhuosheng adds 9% (w) waste magnesia chromium brick fine powder into the magnesia dry material. In industrial applications, it can meet the requirements of steel pouring time and number of furnaces. It has good slag resistance and has good offline erosion thickness. Within 1/3, the middle package will easily disintegrate.
Yu Jiuli and others used waste magnesia-chromium brick particles as aggregate, fused magnesia fine powder as the matrix, sugar substances as the binding agent, and supplemented with borax. They developed a magnesia-chromium dry material with good slag resistance and excellent slag resistance when turned over. Easy to disintegrate. It provides a new way for the harmlessness and recycling of waste magnesia-chromium bricks.
Utilization of waste magnesia calcium bricks
Zhang Wei et al. used the regenerated magnesia-calcium sand and modified magnesia-calcium sand from the original brick layer of post-AOD furnace magnesia-calcium bricks as aggregates, and the mid-grade magnesia as fine powder to prepare a magnesia-calcium tundish dry material. Its volume density, The normal temperature flexural strength and compressive strength are close to those of magnesia dry materials; the shrinkage after burning at 1550°C is greater than that of magnesia dry materials, but it can also meet the performance requirements of dry materials.
Prospects
As the fourth generation working lining, dry materials for continuous casting tundish have many advantages. Among them, magnesium-calcium dry materials and magnesia-forsterite dry materials can respectively remove inclusions in molten steel and improve the cleanliness and purity of molten steel. There are more and more studies on the advantages of reducing energy consumption and production costs. At the same time, the application of composite binders and environmentally friendly binders has gradually replaced single phenolic resin-bound dry materials, with more excellent performance and environmentally friendly performance requirements. The use of medium-temperature binders and additives (toughening agents and anti-slag erosion penetrants) greatly improves the safe performance of dry materials and extends the service life of the tundish. The application of recycled materials allows dry materials to greatly reduce costs while meeting performance requirements.
However, there are also some problems with environmentally friendly binders and medium-temperature binders. For example, Na2SiO3·9H2O, Na2SiO3·5H2O, solid water glass, sodium tripolyphosphate and other silicates or phosphates all contain a lot of Na+ and are difficult to use at high temperatures. Glassy substances will be formed during the process, which affects the service life of the dry materials to a certain extent; sodium tripolyphosphate and sodium hexametaphosphate contain more phosphorus and will add phosphorus to the molten steel; sugars such as polyhydroxy sugars and glucose Although it is smokeless or less smokey at high temperatures, it still has a certain amount of residual carbon at high temperatures, which will carbonize the molten steel, which is detrimental to the smelting of ultra-low carbon steel and high-quality steel; boric acid, borax and Borate glass, because it contains boron, will add boron to the molten steel during use. This is not suitable for smelting steel types that require higher boron content and will affect its hardenability.
At the same time, the research on anti-slag erosion penetrants has not yet formed more theories and more effective methods; there are still few research reports on the application of recycled materials; waste magnesia bricks, waste aluminum magnesium carbon bricks, and waste corundum spinel prefabricated There are few reports on the application of blocks, etc. in dry materials; however, these recycled materials are also feasible as part of the raw materials in dry materials.
Therefore, the next step for researchers and developers of refractory materials is how to find better-performing and more environmentally friendly binders to meet the requirements for producing high-quality steel and clean steel; how to develop and find ways to improve the resistance of dry materials to slag erosion and penetration Other theories, methods and raw materials; how to apply broader recycled material resources to dry materials to meet the tundish smelting requirements, while further reducing the production cost of dry materials and reducing the unit consumption of products. These are issues that need to be addressed urgently.
