This article describes what castables and refractory bricks are used in ladles.
Keywords: ladle; castable; refractory bricks
Ladle, also called ladle, is an important container in the metallurgical industry. It plays the role of storing and transporting molten steel, and also performs the dual task of refining outside the furnace. With the development of steelmaking technology, refractory materials for ladles in my country have also been developed. Very good development. 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. Especially with the increase in the life of the converter, the increase in the continuous casting ratio and the advancement of out-of-furnace refining technology, the ladle is under increasingly harsh operating conditions such as large capacity, multiple steel types, high temperature, and long time, and the requirements for refractory materials for the ladle are are also constantly improving, so 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 pouring ladles
In my country, for ordinary converter ladles with a nominal capacity of less than 50 tons without refining, the working lining is generally formed by integral pouring with castables. The one-time service life of the working lining is generally about 50-60 times, the highest is about 70-80 times, and even more than 100 times in some steel plants. In order to reduce the consumption of refractory materials per ton of steel, many steel mills clean the remaining steel and residue on the surface of the ladle working lining after using it for a certain number of times, commonly known as peeling, and then sit on the tire mold to pour a certain thickness of castables, which are then dried. Continuing to put into use after baking can greatly reduce costs. This process is also called sleeve pouring. The residual lining left in the first time is equivalent to a permanent lining and can last for 2-3 services. The materials of the ladle working lining include alumina-magnesite, high-alumina spinel, etc. According to the binder, it can be divided into low cement, ultra-low cement and cement-free refractory castables.
High alumina spinel castable
Since the promotion and application of amorphous refractory materials lined with ladles in the 1980s, the original ordinary aluminum-magnesium castables have been developed into aluminum-magnesium spinel castables, and the performance of the castables has been significantly improved. Aluminum-magnesia spinel castable has the advantages of high density, high strength, corrosion resistance, spalling resistance, and low wear rate. It can significantly increase the package age, so it is adopted by many manufacturers. The lining construction process has evolved from ramming, projection, and vibration to tire mold vibration. The tire mold vibration reduces the consumption of ladle refractory materials. Achieving good results, the average ladle wrapping age can reach 70-80 times. It has the advantages of uniform vibration, easy operation, high labor efficiency, and can realize continuous ladle lining casting. Its physical and chemical indicators are shown in Table 1.
Table 1 Physical and chemical indicators of high alumina spinel casting materials
| project | Content | Indicators |
| chemical composition,% | MgO+Al₂O₃ | 80-90 |
| Bulk density, g/cm³ | 110℃×16h 1550℃×3h | 2.85 2.80 |
| Flexural strength, MPa | 110℃×16h 1550℃×3h | 8 10 |
| Line change rate, % | 110℃×16h 1550℃×3h | ±0.1 ±4.0 |
Low cement refractory castable
Low-cement refractory castables are developed on the basis of clay combined with refractory castables. They are also a new generation of refractory castables that flourished in the 1980s. Its main varieties include low cement, ultra-low cement and cement-free refractory castables. It combines the advantages of various refractory castables and has the characteristics of high density, low porosity, high strength, low wear, thermal shock resistance and corrosion resistance. , it also has the characteristics of strong volume stability and low construction water consumption, so it is widely used, has good use effects and significant social and economic benefits. Table 2 shows the performance data statistics of low cement, ultra-low cement and cement-free castables.
Table 2 Performance of low cement, ultra-low cement and cement-free castables
Element | A | B | C | LCA | LCB | ULC | CFA | CFM | |
| Aluminum oxide, % Silicon oxide, % Calcium Oxide,% Amount of water added, % | 94–59 | 94–59 | 96–38 | 98426 | 95–27 | 99– <1 6 | 100– 2 4-5 | 92 8 2 4-5 |
Volume density, g/em3 | 110℃×16h1000℃×3h1500℃×3h1650℃×3h | – – – – | 2.812.672.8 – | 2.962.82.932.94 | 2.952.932.99 – | 2.872.842.952.96 | 3.2 3 3.1 3.1 | 3.2 3.2 3.2 3.2 | 3 3 3.1 3.1 |
Porosity, % | 110℃×16h1000℃×3h1500℃×3h1650℃×3h | – – – – | 17.525.523.7 – | 15.323.719.5 – | 18.321.919.7 – | 11191715 | 15.7–18.516.5 | 14.8–17.913.9 | 13.6– 12.7 11.7 |
Flexural strength, MPa | 110℃×16h1000℃×3h1500℃×3h1650℃×3h | – – – – | 5.35.44.5 – | 4.73.76.5 – | 2.52.17.2 – | 4.711.0 – – | 3010.012.013.0 | 3.09.012.020.0 | 3.0 9.0 18.0 15.0 |
Introduction to refractory bricks for ladles
Aluminum silicate material
Clay bricks
Clay bricks are the earliest refractory materials used in ladles in my country. In the 1950s and 1960s, the refractory materials used in ladles in my country were mainly various clay bricks. Due to their low cost, some steel plants still used clay bricks in their ladles until the 1980s. . The physical and chemical indicators of clay bricks used for ladles in a steel plant are: Al2O3 44.10%, SiO2 52.10%, Fe2O3 1.72%, apparent porosity 16% ~ 18%, and normal temperature compressive strength 54.9 ~ 96.0MPa. The service life of clay ladle lining bricks varies depending on the usage conditions of each steel plant. Although clay bricks are no longer used in ladles in my country, clay bricks made a significant contribution 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 output and quality, clay ladle lining bricks have a short service life. Since the late 1960s, some steel plants in my country have begun to use various high-aluminum lining bricks for ladles. The service life of the ladle is greatly improved.
Wuhan Iron and Steel’s 270t open-hearth ladle began to use second-grade high-alumina bricks in 1968. By 1970, the ladle age reached 25.7 times, which was 2.5 times that of clay lining bricks. In 1974, the age reached 31.5 times. The 70t ladle for the No. 2 steelmaking converter of Wuhan Iron and Steel Co., Ltd. has been using high-aluminum bricks with an Al2O3 content greater than 72% since 1980. The ladle age is 34 times and the highest is 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 wall, with an average ladle age of about 50 times. After the continuous casting machine was put into operation, the usage 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-expanded high-alumina bricks with excellent performance. In April 1992, the products produced by Factory A were officially used. The average service life is 81.5 times, and the maximum service life reaches 100 times. The average service life of products from Factory B is 78.6 times, with a maximum of 122 times (continuous casting ratio 55.73%).
Taigang’s 70t ladle uses high-aluminum lining bricks and has a service life of 64.3 times.
In short, the use of high-aluminum lining bricks for ladles in my country has significantly improved the service life of ladles, ensured the smooth progress of steelmaking production, and promoted the further development of the steelmaking industry.
Wax stone bricks
Pyrophyllite brick is a fired product produced with pyrophyllite as the main raw material. In the early 1970s, the waxstone ladle bricks produced by a refractory factory in Fujian were tried on different types of ladles of Maanshan Iron and Steel, Anshan Iron and Steel, Shanghai Steel No. 3 Plant, Sanming Steel Plant and other steel companies. The results show that the performance of wax stone bricks is better than that of clay bricks and third-grade high alumina bricks used at that time. Used on Maanshan Iron and Steel 15t ladle, the service life reaches 66 times. The 70t ladle of Wuhan Iron and Steel No. 2 Steelmaking Plant also tried the wax stone bricks with 72% SiO2 content produced by the plant, but the effect was not ideal and the service life was only 14 times. Baosteel’s 300t ladle used waxstone bricks imported from Japan from September 1985 to 1988, with an average lifespan 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 normal temperature compressive strength 32.9 ~ 62.9MPa. Due to various reasons, waxstone bricks have not been popularized and applied in ladles in my country.
Aluminum-magnesium (carbon) materials
Aluminum-magnesium unburned bricks
In addition to aluminum-magnesium ramming materials and aluminum-magnesium castables, my country has also developed aluminum-magnesium unburned bricks bonded with water glass, which are used on ladles and have a longer life than traditional aluminum silicate ladle bricks. Benxi Iron and Steel’s 160t ladle uses aluminum-magnesia unburned bricks, with an average service life of 40.56 times, which is more than double that of using third-grade high-alumina bricks (lifespan of 18.5 times). The average service life of the aluminum-magnesium unburned bricks used in the 20t ladle of Tianjin No. 3 Steelmaking Plant is 38.8 times, with a maximum of 55 times, which is more than four times the service life of clay lining bricks (9 times).
Alumina-magnesia carbon brick
The 1990s was a period of rapid development of continuous casting technology in my country, and high-efficiency 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-magnesia carbon bricks for ladles, which are used in various types of continuous casting ladles, greatly increasing the service life of ladles. The aluminum-magnesium carbon ladle bricks jointly developed by Luonai Institute, Baosteel and a refractory factory in Jiaozuo are used on Baosteel’s 300t continuous casting ladles. The ladle age has increased from more than 20 times using first-class high alumina bricks to more than 80 times, with the highest reaching 126 times. The 200t fully continuous casting and out-of-furnace refining ladle of Angang No. 3 Steelmaking uses alumina-magnesia carbon bricks, with an average lifespan of 64 times and a maximum of 73 times. In 1993, the promotion and use of high-quality aluminum-magnesia-carbon bricks for ladles was fully launched in my country. Many steelmaking plants across the country, based on the actual situation of the enterprise, successively used aluminum-magnesium-carbon ladle lining bricks, which significantly improved the life of the ladle, such as Panzhihua Iron and Steel Co., Ltd. 160t After using alumina-magnesia carbon lining bricks for ladles, the average service life is increased to 90 times, with a maximum of 115 times. Alumina-magnesia carbon bricks are unfired products made of special-grade high-alumina clinker, fused magnesia or sintered magnesia and graphite as raw materials, and liquid phenolic resin as a binder.
High-grade aluminum-magnesium unburned bricks
Carbon-containing ladle lining bricks will cause carbonization of molten steel during use, which is very detrimental to 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 non-burning bricks (carbon-free non-burning bricks) were developed. Compared with the water glass-bonded aluminum-magnesium unburned bricks developed in the early 1980s, high-grade aluminum-magnesium unburned bricks are a qualitative leap forward. In addition to using high-purity raw materials (corundum, high-purity fused magnesite and high-purity aluminum-magnesium spinel, etc.), the binder also uses high-performance composite binders.
High-grade aluminum-magnesium unburned bricks have achieved good results when used on ladles. Their service life reaches or even exceeds that of carbon-containing ladle lining bricks, while reducing the carbonization of molten steel. For example, the aluminum-magnesia non-burning bricks developed by a refractory company in Henan are used on 100t ladles and LF refining ladles in a steel plant. Their service life is 1.5 times that of aluminum-magnesia carbon bricks. Angang’s 200t ladle uses aluminum-magnesium unburned bricks for more than 110 times, with a maximum of 128 times. The service life of the 170t continuous casting ladle reaches 119 times, which exceeds that of alumina-magnesia carbon bricks. Baosteel’s 300t continuous casting ladle stopped using alumina-magnesia carbon bricks in June 1998 and began to use high-grade alumina-magnesia unburned bricks.
magnesium carbonaceous material
Magnesia carbon brick
Magnesia carbon bricks have excellent corrosion resistance and spalling resistance. Magnesia carbon bricks are mainly used in the slag line area of the ladle, while other refractory materials (castables, unfired bricks, etc.) are used in non-slag line areas, which can not only achieve a higher service life but also reduce the cost of refractory materials. The physical and chemical indicators of the magnesia carbon bricks used in the ladle slag line of a steel plant are: MgO77.4%, C16.75%, apparent porosity 3.1%, bulk density 2.903g/cm, and normal 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. However, the high alumina bricks in non-slag line parts were seriously damaged and were discontinued. Baosteel’s 300t ladle slag line has used MT-14A magnesia carbon bricks since July 1989, and the life of the slag line has remained above 100 times. The 90tLF refining ladle slag line of a steel plant uses magnesia carbon bricks with a carbon content of about 16%, and the slag line life is 95 times. There are also steel plants whose ladles are lined with all-magnesia carbon bricks. For example, the electric furnace of a steel plant uses a 60tLF-VD refining ladle, which is lined with all-magnesia carbon bricks. The average service life is 47 times, with a maximum of 57 times.
Low carbon magnesia carbon bricks
The use of magnesia-carbon bricks in ladle slag lines has the problem of carbonization of molten steel. In recent years, some steel mills 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 a carbon content of less than 7% and less than 5%. The service life can reach about 110 times, which is equivalent to ordinary magnesia-carbon bricks and can basically meet the usage requirements of a 300t ladle. The slag line of Anshan Iron and Steel Ladle also uses low-carbon lining bricks with a carbon content of less than 5%, and the results are good.
Magnesium calcium (carbon) materials
Unfired magnesia calcium bricks
In the early 1990s, Luonai Institute developed unburned magnesia-calcium bricks for ladles using synthetic magnesia-calcium sand and fused magnesia sand as raw materials, and solid inorganic salts and inorganic salt solutions as binding agents. Used on 40tLF-VD refining ladles, the service life is more than 40 times, and the oxygen content in the steel 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 Great Wall Special Steel It is used on the refining ladles of steel plants such as factories.
In recent years, a refractory material company has developed anhydrous resin-bonded unburned magnesia-calcium bricks, which are 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 1.37mm/time.
From July to August 2006, Shandong Magnesium Mine cooperated with a refractory material factory to develop unburned magnesia-calcium bricks, which were used in the non-slag line part of the wall of a 90tLF refining ladle (refining rate 100%) in a steel plant, with a service life of More than 60 times. The breathable bricks at the bottom of the package were discontinued due to serious corrosion. The thickness of the remaining unburned magnesia calcium bricks is about 130mm and can still be used. It is expected that the normal package age can reach 80 to 100 times.
Unfired magnesia-calcium carbon bricks
At the beginning of this century, Shougang No. 2 Steelmaking Plant cooperated with a refractory 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. It is used in the non-slag line part of the 225t ladle of Shougang No. 2 Steelmaking Plant (magnesia carbon bricks for slag line), with an average service life of 116.8 times. Compared with the original alumina-magnesia carbon bricks, when the ladle wall is thinned by 20mm, the average Lifespan increased by 37.57 times. Moreover, the oxygen content and non-metallic inclusions in steel have been reduced.
There are also some steel plants that use magnesia-calcium carbon bricks in the slag lines of various refining ladles such as SKF and LF-VD, and have achieved good results.