The steel plant introduced a 90-ton FUCHS electric furnace in 1994. Based on the successful application of various energy-saving technologies in the 90-ton electric furnace, it introduced four 100-ton FUCHS ultra-high power AC arc furnaces.
Its electric furnace and subsequent solutions use advanced new technologies such as scrap steel priority utilization and foam slag technology to produce high-quality non-torsion controlled cold and hot rolled wires, including prestressed steel strands, cord steel and other 19 series and more than 100 varieties of high-quality products.
With the continuous development of electric furnace steelmaking technology, new requirements have been put forward for refractory materials.
Technological progress promotes the upgrading of refractory materials
The “one ladle to the end” technology reduces the consumption of ladle refractory materials.
During the preparation and construction of the 400 cubic meter blast furnace in 1998, the steel plant implemented the “one ladle to the end” design concept, using heavy trucks to transport ladles and directly adding molten iron to the electric furnace or converter, eliminating torpedo tank cars and the corresponding ladle pouring, weighing and maintenance systems, bringing ironmaking and steelmaking to a higher level.
In 2004, the “one ladle to the end” design concept was applied to the 6.5 million tons of steel plate system project. The “four slurries in the same direction” design concept was adopted, and the ladle successfully received molten iron directly from the blast furnace ironmaking plant, and then directly added it to the converter after being transported to the desulfurization site, effectively shortening the ladle turnover time, reducing the temperature drop of molten iron, and reducing the consumption of refractory materials for the ladle.
Noble, the use effect of refractory materials depends on their performance. The fragility management index of refractory materials is not completely consistent with the actual use effect. Enterprises should combine their own reality to accurately determine the best combination point of refractory materials and production process performance, so that refractory products can maintain stability during high-quality use.
Since 2000, the steel plant has implemented a comprehensive integrity management model for refractory materials, strengthened communication within the plant and between refractory material suppliers, promoted the improvement of steelmaking and refractory material technology and management level, and realized the vision of win-win and common development for both supply and demand sides.
The refractory material of the permanent layer of the ladle is made of high-alumina castable, and the working lining is made of Al2O3-SiC-C bricks. The content of Al2O3, SiC, FC, as well as the apparent porosity, bulk density, compressive strength and other indicators are strictly controlled. The average number of subsequent refractory ladles exceeds 1,150.
The domestic steel stock is relatively low, and scrap steel resources are far from meeting the needs of the rapid growth of steel production. With the application and improvement of new technologies such as hot charging of hot metal in electric furnaces, electric furnace steelmaking faces new opportunities and challenges. If electric furnace steelmaking is to survive and develop, it must focus on the production of electric furnaces.
With the continuous strengthening of cost control in the market and the upgrading of product quality, the hot charging process of electric furnaces in steel mills has been continuously improved and perfected. Electric furnace steelmaking plants have gradually carried out a series of technical transformations and optimizations on the original electric furnace related equipment and operation methods:
First, the electric furnace hot metal drying furnace technology was developed, which changed the previous mode of using scrap steel for drying furnaces for new electric furnace linings;
Second, the electric furnace full blowing model was developed, which realized the converter production under the condition of high iron-water ratio of electric furnaces;
Third, it was found that electric furnace steelmaking should be based on the comprehensive consideration of factors such as raw material conditions and raw material prices, mainly the coordinated use of raw materials to achieve maximization;
Fourth, the application of carbon oxygen gun blowing technology effectively reduced the radiation of arc light on the furnace lining and furnace cover, which played a great role in reducing the consumption of refractory materials, reducing noise and improving the environment of steel plants;
Fifth, the steel structure of the furnace body was transformed to extend the remaining furnace lining;
Sixth, the recovery of residual hot slag of the furnace lining, and fourth, the recycling of hot slag was realized.
At present, all refractory materials of electric furnaces are domestically produced.
The top of the electric furnace adopts the full water-cooled top technology. In order to adapt to the working environment of the small furnace cover of the electric furnace being radiated by electrodes, rapid cooling and heating, chemical monitoring of molten steel and slag, and high proportion of molten iron, the refractory sintering material of corundum and fiber steel is used in the electrode triangle area to prefabricate the furnace cover as a whole, which meets the production conditions under the conditions of high iron-water ratio;
The lining bricks of the electric furnace need to use high-quality magnesia-carbon bricks; the furnace bottom adopts mold-beating materials made of high CaO-containing Fe2O3 sintered combined sand and high fused magnesia sand, the evaporation layer is thin and dense, the hot strength is good, the transition zone is short, and it is easy to complete; the outlet refractory adopts the hot replacement method, and the average life span exceeds 180 furnaces, which solves the problem of not being able to synchronize with the furnace age of the medium repair; the life span of the refractory materials of the electric furnace lining exceeds 1200 furnaces on average, and the consumption and cost of refractory materials have been increasing year by year.
The effectiveness and cost advantage of the use of refractory materials in steel mills’ electric furnaces are due to the management idea of common development of “supply and demand sides”. Both parties jointly strengthen the management of furnace linings, detect and record the thickness of residual bricks after furnace service, and compare it with steelmaking operation parameters. By optimizing electric furnace steelmaking operations and taking measures such as material optimization of refractory materials, production costs are continuously reduced and production efficiency is improved.
Scientific management extends the life of refractory materials in the refining ladle. In order to meet the requirements of high efficiency of electric furnace steelmaking and smelting of special steels, the working lining of Shagang’s refining ladle is mainly made of carbon-containing products. The molten pool and the bottom of the ladle are made of Al2O3-MgO-C bricks, and the line part is made of MgO-C bricks, with an average service life of more than 90 times;
The ladle short-circuit bricks are made of slit-type corundum chromium, with an average service life of more than 33 times; the ladle water inlet and seat bricks are made of corundum zirconium, with an average use of more than 33 times; the average service life of the water outlet and slide plate is more than 3.8 times/set; the outlet is filled with chromium drainage sand, and the self-opening rate of the ladle drainage sand is ≥99% under normal production rhythm.
The steel mill has taken the following measures in the management of ladle refractory materials:
First, strengthen the quality inspection of ladle bricks to ensure the quality of refractory materials for working lining;
Second, strictly control the quality of masonry to ensure that it meets the requirements of masonry technology;
Third, strictly control the quality of new ladle baking to ensure thorough baking
Fourth, strictly operate the refining process to control the refining steel temperature and furnace alkali slag degree;
Fifth, implement a reasonable blowing system to ensure good construction quality.
The high quality of continuous casting billets places high demands on refractory materials. In order to meet the production needs of large quantities and high-quality steel, modern steel mills have developed continuous casting technology in the direction of high pulling speed, high peak value and peak value.
The continuous casting machine in the electric furnace workshop of a steel plant with a capacity of more than 90 tons is 5-6 strands, the cross-section of the square billet is 150 mm × 150 mm, and the heat delivery ratio of the continuous casting billet reaches more than 70%, which puts forward requirements on the quality of the continuous casting billet.
In order to maximize the average residence time of molten steel in the tundish, promote the aggregation and flotation of inclusions, and improve the flow characteristics of molten steel in the tundish, the steel plant cooperated with colleges and universities to design a new flow control device, which minimized the inclusions in the tundish, made the temperature distribution uniform, the temperature difference between each flow small, and significantly improved the quality of the continuous casting billet.
The tundish covering slag also plays an important role in controlling the quality of continuous casting billets. Its main functions are as follows:
First, it is heat-insulating and heat-preventing drying;
Second, it prevents secondary oxidation of molten steel;
Third, it absorbs inclusions that float to the slag interface. The sand tundish covering slag adopts high basicity, low Al2O3 activity, and low MnO+FeO content. It has the characteristics of strong melting and dissolving inclusions. Adding MgO to the slag can play a short-term role in the long nozzle and the tundish slag line.
The tundish insulation layer adopts composite insulation board. Compared with the traditional insulation layer, it has good wall insulation effect, and the temperature of the tundish and the water temperature of the steel are significantly reduced, which is conducive to the stable control of the molten steel temperature;
The permanent layer adopts high-strength magnesium-aluminum castable; the working layer adopts magnesium dry material, which has the advantages of convenient construction, high thermal efficiency, fast turnover, long service life, and residual lining.
Good disintegration performance and low melting; in order to further reduce the inclusions and pinhole defects in the continuous casting billet, eliminate the infusion phenomenon caused by the deposition of high melting point materials on the inner wall of the nozzle during the production process of low-carbon aluminum killed steel, and meet the production of multiple furnaces, a wide-band anti-rust immersion nozzle is adopted, and the continuous casting time is not less than 8 hours, which meets the clean production requirements.
Technological development brings new demands
In recent years, the continuous development of electric furnace smelting technology has also put forward new demands and requirements for refractory materials, mainly including the following aspects.
Electric furnace: In order to meet the high-efficiency production of electric furnace, intermittent carbon oxygen guns and oxygen oil burners are added. The high temperature generated by these nozzles increases the oxidation of slag, causing erosion of the furnace lining and furnace top refractory materials. Even if the method of adjusting the nozzle combustion speed in a timely manner during the smelting cycle is adopted to reduce the impact on the refractory materials of the furnace lining, the negative impact on the refractory materials is still significant, offsetting the further extension of the furnace life. How to meet the requirements of high-efficiency production of electric furnace refractory materials is a topic that requires joint research, discussion and research by steel mills and refractory material suppliers.
The application of new technology of bottom blowing and stirring in electric furnaces increases the damage to the local refractory materials at the bottom of the furnace, so it must be monitored and maintained during the entire service life of the furnace lining.
The safe use and extended service life of the bottom blowing components of electric furnaces are urgent issues to be solved.
The application of full refining and blowing technology in electric furnaces has put forward new challenges to the service life of furnace roof refractory materials. The development, design and application of new furnace roof refractory materials are the key to extending the service life of the furnace roof and reducing costs.
Ladle: In the steelmaking system, the proportion of refractory cost of refined ladle increases, and it is the largest consumer of refractory materials. The gap between the life of ladle of steel mills and that of advanced steel enterprises is widening. Further extending the life of ladle is the development direction to ensure clean production and reduce refractory consumption.
In addition, electric furnaces and ladles will generate a large amount of waste magnesia carbon bricks, waste refractory raw materials and recycled products. The formulation of standards is of great significance to regulating the healthy development of the industry, ensuring users’ safe and secure use, reducing costs, protecting the environment and saving resources.
Continuous casting: Tundish heat turnover can reduce the amount of refractory materials in the tundish.
This technology has been applied in steel enterprises, which not only improves the quality of steel in non-casting casting processes, but also reduces the cost of refractory materials and increases the labor intensity of workers’ repair.
The flow control structure of the tundish currently used in steel mills is relatively complex and is not suitable for heat turnover operations. With the continuous development of refining technology, the chemical composition and temperature adjustment of molten steel, the addition of elements and inclusions, etc. are basically completed in the ladle, and the tundish is also developing towards structural design and simplified operation. Designing and developing a simple tundish cavity and using long-metered tundish lining refractory materials are necessary conditions for achieving heat turnover of tundish refractory materials.
