Abstract: Ladle, also called steel ladle, is an important container in the metallurgical industry. It plays the role of storing and transporting molten steel. At the same time, it also has the dual task of refining outside the furnace. With the development of steelmaking technology, the refractory materials for ladle in my country have also been well developed. The length of the service life of the ladle is not only related to the consumption of refractory materials, but also directly affects the normal production of steelmaking. In particular, with the improvement of the life of the converter, the increase in the continuous casting ratio and the advancement of refining technology outside the furnace, the ladle is in increasingly harsh conditions of use such as large capacity, multiple steel types, high temperature and long time. The requirements for refractory materials for ladle are also constantly increasing. Therefore, countries around the world are actively researching and developing various new refractory materials to improve the quality of existing refractory materials, extend the service life of refractory materials, and reduce the ton consumption of refractory materials.
Introduction to the use of cast ladle
In my country, the working lining of ordinary converter ladles without refining with a nominal capacity of less than 50 tons is generally cast as a whole using castables. The one-time service life of the working lining is generally around 50 to 60 times, and the highest is around 70 to 80 times, and even some steel mills have more than 100 times. In order to reduce the consumption of refractory materials per ton of steel, many steel mills clean up the residual steel and residue on the surface of the residual lining after using the working lining of the ladle for a certain number of times, commonly known as peeling, and then put a certain thickness of castables on the tire mold, and continue to put it into use after baking, which can greatly reduce the cost. This process is also called casting. The residual lining left for the first time is equivalent to a permanent lining, which can maintain 2 to 3 packages. The materials of the working lining of the ladle include aluminum-magnesium, high-aluminum spinel, etc., which can be divided into low-cement, ultra-low-cement and cement-free refractory castables according to the binder.
1. High-aluminum spinel castable
Since the promotion and application of amorphous refractory materials for ladle lining in the 1980s, it has developed from the original ordinary aluminum-magnesium castables to aluminum-magnesium spinel castables, and the performance of the castables has been significantly improved. Aluminum-magnesium spinel castables have the advantages of high density, high strength, corrosion resistance, spalling resistance, and low wear rate. They can significantly improve the ladle life and are therefore adopted by many manufacturers. The lining process has developed from ramming, projection, and vibration to tire mold vibration, which reduces the consumption of ladle refractory materials. Good results have been achieved, and the average ladle life can reach 70-80 times. It has the advantages of uniform vibration, simple operation, and high labor efficiency, and can achieve continuous casting of the ladle lining.
2. Low-cement refractory castables
Low-cement refractory castables are developed on the basis of clay-bonded refractory castables. They are also a new generation of refractory castables that have been booming in the 1980s. Its main varieties include low-cement, ultra-low-cement and cement-free refractory castables. It combines the advantages of multiple refractory castables, and has the characteristics of high density, low porosity, high strength, low wear, thermal shock resistance and erosion resistance. It also has the characteristics of strong volume stability and low construction water consumption. Therefore, it is widely used, with good use effects and significant social and economic benefits.
Introduction to refractory bricks for ladle
Alumina silicate clay bricks
Clay bricks are the earliest refractory materials used in ladle in my country. In the 1950s and 1960s, the refractory materials used in my country's ladle were mainly various clay bricks. Due to the low cost of use, some steel mills still used clay bricks in their ladles until the 1980s. The physical and chemical indicators of clay bricks used in the ladle of a steel plant are: Al2O3 44.10%, SiO2 52.10%, Fe2O3 1.72%, apparent porosity 16%~18%, and room temperature compressive strength 54.9~96.0MPa. The service life of clay ladle lining bricks varies depending on the use conditions of each steel plant. Although clay bricks are no longer used in my country's ladle, clay bricks have made significant contributions to the recovery and subsequent development of my country's steelmaking industry in the early days of the founding of the People's Republic of China. High Alumina Bricks
With the continuous development of steelmaking technology and the continuous improvement of steel production and quality, clay ladle lining bricks have a short service life. Since the late 1960s, some steel mills in my country have begun to use various high-alumina lining bricks for their ladles, which has greatly increased the service life of the ladle.
The 270t ladle used in Wuhan Iron and Steel's open-hearth furnace began to use second-class high-alumina bricks in 1968. By 1970, the ladle age reached 25.7 times, which is 2.5 times that of clay lining bricks. In 1974, the ladle age reached 31.5 times. The 70t ladle used in Wuhan Iron and Steel's second steelmaking converter began to use high-alumina bricks with an Al2O3 content greater than 72% in 1980, with a ladle age of 34 times and a maximum of 50 times.
Since June 1986, Baosteel's 300t ladle has used first-class high-alumina bricks produced by a refractory material factory for the entire ladle wall, with an average ladle age of about 50 times. After the continuous casting machine was put into production, the use conditions of the ladle deteriorated and the service life of the ladle lining was shortened. Baosteel cooperated with some refractory material manufacturers to develop micro-expansion high-alumina bricks with excellent performance. In April 1992, the products produced by Factory A were officially used, with an average service life of 81.5 times and a maximum life of 100 times. The average service life of the products produced by Factory B was 78.6 times, and the maximum reached 122 times (continuous casting ratio 55.73%).
Taigang's 70t ladle uses high-alumina lining bricks, with a service life of 64.3 times.
In short, after my country's ladle uses high-alumina lining bricks, the service life of the ladle has been significantly improved, ensuring the smooth progress of steelmaking production and promoting the further development of the steelmaking industry.
Wax stone bricks Wax stone bricks are a fired product produced with pyrophyllite as the main raw material. In the early 1970s, wax stone ladle bricks produced by a refractory material factory in Fujian were tried on different types of ladles of steel enterprises such as Ma Steel, Anshan Iron and Steel, Shanghai Steel Plant No. 3, and Sanming Steel Plant. The results showed that the performance of wax stone bricks was better than the clay bricks and third-class high-alumina bricks used at that time. Used on Ma Steel's 15t ladle, the service life reached 66 times. The 70t ladle of Wuhan Iron and Steel's Second Steelmaking Plant also tried the wax stone brick with a SiO2 content of 72% produced by the plant, but the effect was not ideal, and the service life was only 14 times. Baosteel's 300t ladle used wax stone bricks imported from Japan from September 1985 to 1988, with an average service life of 38 times. The physical and chemical indicators of wax stone bricks for ladles produced by a certain factory are: SiO2 78.95%, Al2O3 18.85%~19.51%, Fe2O3 0.44%~0.52%, apparent porosity 14%~18%, and room temperature compressive strength 32.9~62.9MPa. Due to many reasons, wax stone bricks have not been promoted and applied on ladles in my country.
Aluminum-magnesium (carbon) materials Aluminum-magnesium unfired bricks
In addition to aluminum-magnesium ramming materials and aluminum-magnesium castables, my country has also developed aluminum-magnesium unfired bricks combined with water glass. When used on ladles, they have a longer life than traditional aluminum silicate ladle bricks. Bengang's 160t ladle uses aluminum-magnesium unfired bricks, with an average life of 40.56 times, more than double the use of third-class high-aluminum bricks (life of 18.5 times). The 20t ladle of Tianjin No. 3 Steel Plant uses aluminum-magnesium unfired bricks with an average life of 38.8 times, with a maximum of 55 times, which is more than 4 times the service life of clay lining bricks (9 times).
Aluminum-magnesium carbon bricks
The 1990s was a period of rapid development of continuous casting technology in my country, and efficient continuous casting technology became the focus of its development. In order to improve the service life of continuous casting ladles and meet the needs of the development of efficient continuous casting technology, my country has developed aluminum-magnesium carbon bricks for ladles, which are used in various types of continuous casting ladles, greatly improving the service life of ladles. The aluminum-magnesium-carbon steel ladle bricks jointly developed by Luoyang Institute of Refractory Engineering, Baosteel and a refractory material factory in Jiaozuo are used in Baosteel's 300t continuous casting steel ladle. The service life of the ladle has increased from more than 20 times using first-class high-aluminum bricks to more than 80 times, and the highest has reached 126 times. The 200t steel ladle of Anshan Iron and Steel's third steelmaking plant, which is fully continuous casting and refining outside the furnace, uses aluminum-magnesium-carbon bricks, with an average service life of 64 times and a maximum of 73 times. In 1993, the promotion and use of high-quality aluminum-magnesium-carbon bricks for steel ladles was fully launched in my country. Many steel mills across the country, according to the actual situation of their enterprises, have successively used aluminum-magnesium-carbon steel ladle lining bricks, which has significantly increased the service life of the ladle. For example, after using aluminum-magnesium-carbon lining bricks, the average service life of Panzhihua Iron and Steel's 160t steel ladle has increased to 90 times, and the highest has reached 115 times. Aluminum-magnesium-carbon bricks are unfired products made of special high-aluminum bauxite clinker, fused magnesia or sintered magnesia and graphite as raw materials, and liquid phenolic resin as a binder.
High-grade aluminum-magnesium unfired bricks
Carbon-containing ladle lining bricks will cause carbon increase in molten steel during use, which is very unfavorable for the smelting of clean steel, low-carbon steel and ultra-low carbon steel. In order to meet the needs of clean steel, low-carbon steel and ultra-low carbon steel smelting, high-grade aluminum-magnesium unfired bricks (carbon-free unfired bricks) have been developed. Compared with the aluminum-magnesium unfired bricks combined with water glass developed in the early 1980s, high-grade aluminum-magnesium unfired bricks are a qualitative leap. In addition to using high-purity raw materials (corundum, high-purity fused magnesia and high-purity aluminum-magnesium spinel, etc.), the binder also uses a high-performance composite binder.
High-grade aluminum-magnesium unfired bricks have achieved good results in the use of ladle, and their service life has reached or even exceeded that of carbon-containing ladle lining bricks, while reducing carbon increase in molten steel. For example, the aluminum-magnesium unfired bricks developed by a refractory material company in Henan Province are used in the 100t ladle and LF refining ladle of a steel plant, and their service life is 1.5 times that of aluminum-magnesium carbon bricks. Anshan Iron and Steel's 200t ladle uses aluminum-magnesium unfired bricks, and the ladle life is more than 110 times, with the highest reaching 128 times. The service life of the 170t continuous casting ladle reached 119 times, exceeding the aluminum-magnesium carbon brick. Baosteel's 300t continuous casting ladle stopped using aluminum-magnesium carbon bricks in June 1998 and began to use high-grade aluminum-magnesium unfired bricks.
Magnesium-carbon material magnesium-carbon bricks
Magnesium-carbon bricks have excellent corrosion resistance and anti-stripping properties. Magnesium-carbon bricks are mainly used in the slag line of the ladle, while other refractory materials (casting materials, unfired bricks, etc.) are used in non-slag line areas, which can not only obtain a higher service life, but also reduce the cost of refractory materials. The physical and chemical indicators of magnesium-carbon bricks used in the slag line of a steel plant's ladle are: MgO77.4%, C16.75%, apparent porosity 3.1%, volume density 2.903g/cm, and room temperature compressive strength 38.6MPa. In September 1981, Wuhan Iron and Steel No. 2 Steelmaking Plant took the lead in using magnesia carbon bricks in the 70t ladle slag line, with a service life of 50 times. It was discontinued due to serious damage to high-alumina bricks in non-slag line parts. Baosteel's 300t ladle slag line began to use MT-14A magnesia carbon bricks in July 1989, and the life of the slag line remained above 100 times. The 90tLF refining ladle slag line of a certain steel plant uses magnesia carbon bricks with a carbon content of about 16%, and the life of the slag line is 95 times. Some steel plants also use full magnesia carbon brick lining for their ladles. For example, a steel plant uses a 60tLF-VD refining ladle for electric furnaces, which is lined with full magnesia carbon bricks, with an average life of 47 times and a maximum of 57 times.
Low-carbon magnesia carbon bricks
The use of magnesia carbon bricks in the ladle slag line has the problem of carbonization of molten steel. In recent years, some steel plants have cooperated with refractory manufacturers to develop low-carbon magnesia carbon bricks for ladle slag lines. Baosteel's 300t ladle slag line has tried low-carbon magnesia-carbon bricks with carbon content less than 7% and less than 5%, and the service life can reach about 110 times, which is equivalent to ordinary magnesia-carbon bricks and can basically meet the use requirements of 300t ladle. Ansteel's ladle slag line also uses low-carbon ladle lining bricks with a carbon content of less than 5%, and the use effect is good.
Unburned magnesia-calcium bricks for magnesia-calcium (carbon) materials
In the early 1990s, Luoyang Institute of Refractories used synthetic magnesia-calcium sand and fused magnesia sand as raw materials, solid inorganic salts and inorganic salt solutions as binders to develop unburned magnesia-calcium bricks for ladles. It was used in a 40tLF-VD refining ladle in a steel plant in Shanghai. The service life is more than 40 times, and the oxygen content in the steel has dropped from 12.2×10-6 to 11.13×10-6. In 1992, the product passed the appraisal of the former Ministry of Metallurgy, and was later used in the refining ladles of steel plants such as Changcheng Special Steel Plant.
In recent years, a refractory company has developed an unburned magnesia-calcium brick combined with anhydrous resin, which is used in a steel company's 100tLF refining ladle, with a service life of 80 to 85 times and an erosion rate of 1.28 to 1.37 mm/time.
From July to August 2006, Shandong Magnesium Mine cooperated with a refractory factory to develop an unburned magnesia-calcium brick, which was used in the non-slag line part of the ladle wall of a steel plant's 90tLF refining ladle (refining rate 100%), with a service life of more than 60 times. It was discontinued due to severe corrosion of the air-permeable bricks at the bottom of the ladle. The thickness of the remaining unburned magnesia-calcium bricks is about 130 mm, and it can continue to be used. It is expected that the normal ladle life can reach 80 to 100 times.
Unburned magnesia-calcium carbon bricks
At the beginning of this century, Shougang No. 2 Steelmaking Plant cooperated with a refractory material company to develop unburned magnesia-calcium carbon bricks using synthetic magnesia-calcium sand, fused magnesia sand and high-purity graphite as raw materials and anhydrous resin as a binder. They were used in the non-slag line of the 225t ladle of Shougang No. 2 Steelmaking Plant (magnesia-calcium bricks for slag line), with an average service life of 116.8 times. Compared with the original aluminum-magnesium carbon bricks, the average service life increased by 37.57 times when the ladle wall was thinned by 20mm. The oxygen content and non-metallic inclusions in the steel were reduced.
Some other steel plants have used magnesia-calcium carbon bricks in the slag line of various refined ladles such as SKF and LF-VD, and achieved good results.
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