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                Relationship between refractories and metallurgy

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                Relationship between refractories and metallurgy

                Date of release:2018-09-05 Author: Click:

                Relationship between refractories and metallurgy

                Refractory is widely used in metallurgical industry. Alkaline refractories are widely used in steelmaking equipment because of their good properties. The interaction between refractories and molten steel and its influence on the quality of molten steel and steel: non-metallic inclusion in molten steel and steel; Influence of carbonization of refractories on molten steel and steel quality; The desulfurization of refractory is helpful to improve the quality of molten steel and steel. The dephosphorization of refractory is helpful to improve the quality of molten steel and steel.

                According to its chemical properties and composition, refractories can be generally divided into: acid refractories (quartz, silica brick); Semi-acidic refractory (semi-silica brick); Neutral refractory (chrome brick, clay brick, high alumina brick); Basic refractories (magnesia brick, chrome-magnesia brick, magnesia alumina brick, dolomite brick, magnesia sand, dolomite and magnesia refractory mud), etc. Alkaline refractories are widely used in smelting equipment because of their excellent properties such as high fire resistance, good thermal stability and slag resistance.

                In the process of bof and eaf steelmaking, the molten steel will cause mechanical scour to the lining refractory, at the same time, the constituent elements of the refractory will dissolve into the molten steel and react with the molten steel. The mechanical scour of molten steel on lining and the chemical reaction between them: on the one hand, the damage and erosion of lining refractories are caused; On the other hand, it will affect the quality of molten steel and steel. In the process of steel smelting, the interaction between furnace lining refractory and molten steel in the molten pool and the resulting impact on molten steel and steel quality are mainly as follows:

                1. When refractory falls off, non-metallic inclusions are generated in the molten steel and steel during the steelmaking process. When the lining refractory brick is eroded, the decarbonization layer and the reaction layer of the brick will be loosened due to structural changes. Due to the mechanical erosion of molten steel, slag, furnace gas, molten iron and the addition of bulk materials and scrap steel, the refractories fall off and become involved in the steel solution, forming non-metallic inclusions. The nonmetallic inclusions in steel are quite different from the properties of steel. From the mechanical point of view, the presence of non-metallic inclusions is the stress concentration point of steel, which has a great impact on the strength, stiffness, endurance limit and other mechanical properties of steel. Therefore, non - metallic inclusion is one of the serious defects affecting the quality of steel.

                Two, refractory elements and non-metallic elements in the molten steel react with each other to produce non-metallic inclusions to form some elements of the refractory, directly dissolved into the molten steel, making the pool of oxygen, carbon and other non-metallic elements increase. Under certain conditions, nonmetallic inclusions are formed by the interaction of nonmetallic elements in molten steel. In the same way, the quality of molten steel and steel will be adversely affected.

                At present, it is widely used in converter, electric furnace, continuous casting, furnace refining and ladle refractories at home and abroad. It is a relatively new type of basic refractories developed in the 1980s -- carbon composite refractories. Carbon composite refractories generally contain 3% ~ 30% carbon. Oxidation of carbon is an important reaction in smelting process. It is one of the important tasks of steelmaking to reduce the carbon content in the molten steel to the specifications of the steelmaking number.

                The decarbonization of refractories will cause the increase of carbon content in molten steel and change the composition of steel, especially in the smelting of pure steel and ultra-pure steel, the decarbonization of refractories will have a greater impact on the quality of molten steel and steel. The decarburization mechanism of refractories is as follows: when smelting is carried out to a certain extent, there is a certain liquid phase isolation layer between steel and refractories. The reactant forms a solid phase product layer on the surface of the refractories through which the constituent elements of the refractories diffuse into the molten steel. However, some elements and oxides in molten steel, mainly FeO in steel slag, pass through the reaction layer of firebrick to the decarbonization layer reaction interface.

                Thus, the composition of molten steel is affected. The chemical reaction formula is: (FeO)+C(solid)=[CO]+Fe slag O2+2C(solid)=2[CO] furnace gas. In addition, oxygen blowing and decarbonization should be carried out in the converter and electric furnace during smelting. Oxygen [O2] oxidizes a large amount of atomic iron [Fe] in the molten pool into [FeO], and carbon [C] dissolved in molten steel contacts with [FeO] for oxidation reaction. After the carbon is oxidized, CO bubbles are formed to merge and grow up and then float up to be discharged through the slag layer. The oxidation of carbon will affect the content of oxygen and other components in molten steel. Therefore, it will also have some impact on the quality of molten steel and steel. However,[CO] bubbles' rising and discharging have a strong stirring effect on the molten metal pool, and have certain benefits on the composition and temperature of uniform molten steel and improving the dynamic conditions of chemical reaction of molten steel.

                Fourth, the desulfurization of refractories is conducive to improving the quality of molten steel and steel sulfur in the form of sulfide in steel, for the vast majority of steel, sulfur [S] is a harmful element. Its main effect on the properties of steel: making the steel hot brittle, reducing the mechanical properties and welding properties of steel. Therefore, reducing and controlling the sulfur content in steel is of great benefit to improving the quality of steel. The experimental results show that there is liquid phase formation inside the refractory at high temperature. The liquid layer between molten steel and refractory, usually silicate melt, its composition, structure and slag is very similar.

                Therefore, also has the slag REDOX; Desulphurization, phosphorus and adsorption of inclusions in molten steel. The desulfurization principle of refractory to molten steel in molten pool is as follows: sulfur ions entering the liquid phase isolation layer of refractories diffuse into the refractories through the liquid phase, react with CaO particles in the refractories, and generate CaS layer on the surface of CaO particles. The chemical reaction formula is :(CaO)+[S]=(CaS)+[O], which indicates that CaO has a strong desulfurization effect. Therefore, the refractory containing mgo-cao series has a strong desulphurization effect.

                5. The dephosphorization of refractories is conducive to improving the quality of molten steel and steel. Phosphorus exists in the form of iron phosphide in steel, and is a harmful element for most steels. Its main influence on the properties of steel is to reduce the plasticity, toughness, welding resistance and cold brittleness of steel. The dephosphorization of refractory is the same as that of slag. The basic principle is: phosphorous oxidation in molten steel produces P2O5. As the P2O5 gas is unstable, it must float to the liquid surface of slag and molten steel and react with the basic oxides provided in the liquid phase layer of refractories to form phosphates and dissolve into slag, so that phosphorus is discharged from molten steel. Its chemical reaction formula is :2[p]+5(FeO)+4(CaO)=(4CaO.P2O5)+5[Fe]. Therefore, refractories can remove certain content of phosphorus in molten steel, which is conducive to improving the quality of molten steel and steel.

                In recent years, due to the rapid development of industry, national defense and aerospace industry, the demand for high-quality steel is increasing. In smelting pure steel and other high quality steel, we must pay great attention to and deeply study the influence of the reaction between refractories and molten steel in the molten pool on the quality of steel. At the same time, it provides a basis for the research and development of new refractories which can purify molten steel. At present, China consumes about 8 million t of refractories every year, and more than 3 million t of discarded refractories are used.

                If these post-use refractories are selected, classified and treated by special processes, they can be used as refractory materials with high value. After processing with these raw materials, not only can produce high quality amorphous refractories, but also can regenerate high quality shaped products, some can be used as metallurgical accessories, such as slag splashing furnace charge, slag making agent, but also in the construction, cement and agricultural applications. This not only saves the country's mineral resources and energy, but also reduces environmental pollution, greatly reducing the cost of refractories.

                Therefore, it is of great significance to study the reuse of post-use refractories. A lot of foreign countries, especially developed countries, attach great importance to the reuse of abandoned refractories, and the development is also very fast, so the reuse rate of refractories are generally higher, such as some steel mills have reached more than 80%. Some companies cooperate with universities and research institutions to conduct in-depth research on the reuse of discarded refractories. Some places have set up special recovery and reprocessing of refractory after the company, after the use of refractories are all being used in the direction of development, some enterprises are also in the direction of zero emissions of refractories.

                In Japan, the refractory used in the iron and steel industry is mainly used as slag making agent or slag regulator, but also as a substitute for molding sand; K1203 -- Si02 -- C(ASC) castable in iron ditch has been recycled by 50%, mainly used to make iron ditch amorphous refractory aggregate; After the use of magnesia chrome brick as a partial bottom of the steel outlet filler, its pouring rate is greater than 98%; A-ma castable can be recycled and used as repairing material and spraying material. It can also be reprocessed into firebrick.

                Nippon steel has also developed a production method of long nozzle for continuous casting from waste materials. Ludao iron and steel company has successfully developed the reuse technology of skateboards. They use the method of pouring and restoring castable materials and the method of ring setting to make the service life of the repaired skateboards the same as the new ones. Japan zhiduo steel mill mainly USES waste brick as raw material to develop ramming materials around ladle bottom, ladle pouring materials and shaping products. For example, 85% recycled materials and 15% new materials are used to produce non-burned magnesia bricks for the melting pool of electric furnace, 90% recycled materials and 10% new materials are used to produce magnesia carbon bricks for the slag line of electric furnace, and all the RH bottom fired magnesia chrome bricks produced by recycled materials are used. The performance of recycled brick is shown in table 1, and its use effect is basically the same as the original brick (new brick).

                The reutilization rate of refractories in zhiduo steel plant in Japan reached 50-100%. Project ohm (MgO)/% ohm (C)/% apparent porosity /% volume density /(g.cm-3) compressive strength /MPa erosion speed 1)/(mm.sub-1) recycled brick original brick was founded in 1987, France Valoref company, specializing in the global waste refractory business, invented a lot of recycling from glass, steel, chemical, waste incineration and other industries most of the waste refractory technology. An optimal method for recovery and utilization of furnace was also developed.

                The recycling rate of refractories used in French glass kilns was 24% in 1993 and 60% in 1997. Italian OfficineMeccanichediPonzanoVenetto company developed a recycling all kinds of the stove, iron and steel industry, ingot mould and the tundish ladle lining, using the method of refractory of recovered refractory is to direct injection charging in order to protect the wall. Steel mills in the United States produce 1 million tons of discarded refractories a year, almost all of which are buried and only a few are recycled.

                In 1998, the U.S. department of energy, the department of industry and technology, and steelmakers jointly developed a three-year program to extend the service life of refractories and recycle discarded refractories. Government support and cooperation among manufacturers, users and research institutions have strengthened research on the reuse of post-use refractories. The application scope of recycled refractories is desulfurizer, slag modifier (slag-making agent), slag splashing furnace protection additive, raw material of calcium aluminate cement, refractory concrete aggregate, paving material, ceramic raw material, raw material for glass industry, granular material for roof construction, abrasive and soil modifier, or manufactured into original refractory products. The application of post dolomite brick as soil conditioner and slag making agent was studied in the United States and good results were obtained. Today, the amount of discarded refractories in the United States has been greatly reduced.

                The address of this article:http://www.casademaracaipe.com/en/news/408.html

                Key word:耐火材料,耐火材料生產廠家,推板窯廠家


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