In simple terms, a ladle is a container that can store and transport molten steel during the smelting process. Nowadays, due to the rapid development of the manufacturing industry, the manufacture of some important equipment and instruments requires the continuous improvement of the quality of steel, which requires improving the purity of steel, removing inclusions in molten steel, and strictly controlling the composition of some harmful elements in molten steel. Refining in the ladle can meet this requirement, so refining in the ladle becomes a method to improve the quality of steel, and the ladle has changed from a pure molten steel container to a multi-component container with smelting functions. The structural composition of the ladle is mainly composed of three parts: the shell, the inner lining and the mainstream control mechanism. As shown in Figure 1.1, the structure of the ladle and the refractory materials used in each part.
The ladle shell is welded by the boiler steel plate, and the thickness of the steel plate on the wall and bottom of the barrel is between 14-30mm and 24-40mm. In order to ensure the smooth removal of baking moisture, small holes of 8-10mm are drilled on the ladle shell. The inner lining of the ladle mainly consists of three parts.
The first part is the working layer. The working layer is in direct contact with molten steel and slag during ladle smelting, and is eroded by molten steel and steel slag, and is susceptible to large temperature differences. Therefore, the refractory materials used in the working layer are often severely damaged and need to be inspected and replaced regularly.
The second part is the permanent layer. The thickness is about 30-60mm. The permanent layer is inside the working layer. The permanent layer plays the role of the main frame of the ladle, which plays a vital role in preventing the leakage of molten steel and maintaining the safe operation of the ladle. Therefore, the life of the ladle is related to the quality of this layer. This layer is generally built with clay and high-alumina bricks, usually in a comprehensive way.
The third is the insulation layer. The insulation layer is the outermost layer of the inner lining, close to the steel plate, with a thickness of about 11-15mm. The function of the insulation layer is mainly to keep the molten steel warm, reduce the heat loss of molten steel, and reduce the energy consumption of steelmaking.
Classification of refractory materials commonly used in ladles
|Aluminum silicate||Clay brick, high alumina brick, high alumina ramming material, wax stone brick|
|Aluminum magnesium (carbon) quality||Aluminum-magnesium ramming mass. Aluminum-magnesium castables. Aluminum magnesium does not burn bricks. Aluminum magnesium spinel castable. Aluminum magnesia carbon brick. Al-Mg spinel carbon brick. High-grade aluminum-magnesium non-fired bricks. High-grade aluminum-magnesium spinel castable.|
|Magnesium Carbonaceous||Magnesia Carbon Brick, Low Carbon Magnesia Carbon Brick|
|Magnesium calcium (carbon)||Dolomite ramming material, unburned magnesia calcium brick, unburned magnesia calcium carbon brick|
Aluminum silicate ladle refractory material
Clay bricks are the earliest ladle refractory materials used. In the 1950s and 1960s, the refractory materials used in ladles were mainly various clay bricks. Due to the low cost of use, some steel mills still used clay bricks in ladles until the 1980s.
High alumina brick
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 end of the 1960s, some steel mills began to use various high-alumina lining bricks in the ladles, which greatly increased the life of the ladles.
The 270t ladle for A steel open hearth furnace began to use second-class 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 package age reached 31.5 times. The 70t ladle for the steelmaking converter of Steel A has been using high-alumina bricks with an Al2O3 content greater than 72% since 1980, and the ladle age is 34 times, with a maximum of 50 times.
Since June 1986, the 300t steel ladle of B steel has used first-class high-alumina bricks produced by a refractory material factory for the whole cladding wall, and the average cladding age is about 50 times. After the continuous casting machine was put into production, the service conditions of the steel ladle deteriorated and the service life of the lining was shortened. B Steel cooperated with some refractory manufacturers to develop micro-expansion high-alumina bricks with excellent performance. In April 1992, the products produced by Factory A were officially used. The average service life was 81.5 times, and the maximum life span reached 100 times. The average service life of products using Plant B is 78.6 times, and the highest reaches 122 times (continuous casting ratio 55.73%).
C-steel 70t ladle uses high-aluminum lining bricks, with a service life of 64.3 times.
In short, the use of high-alumina lining bricks in the ladle significantly increases the service life of the ladle, ensures the smooth progress of steelmaking production, and promotes the further development of the steelmaking industry.
|Apparent porosity/%||Normal temperature compressive strength/MPa||Bulk density/g.cm-3|
High alumina ramming material
At the end of the 1970s, some steel mills used high-aluminum ramming material for the ladle lining, and achieved good results. High-alumina ramming material is a kind of amorphous refractory material with good plasticity, which is made of high-quality high-alumina bauxite clinker as raw material (aggregate and fine powder), industrial phosphoric acid as binder, and prepared through batching and mixing. The overall ramming technology is used to make an integral lining, which has a longer service life.
|Ladle category||Ladle capacity/t||Average life expectancy/time||Maximum lifespan/time|
|Open hearth ladle||50||56.8||67|
|Open hearth ladle||100||50|
|Electric furnace ladle||25||67.7||81|
Aluminum-magnesium (carbon) ladle refractory material
Since the 1980s, the steelmaking industry has entered a stage of rapid development. The popularization and application of modern steelmaking technologies such as continuous casting and refining outside the furnace, as well as the increase in clean steel production, have made the use of ladle refractory materials even worse. The rise of molten steel temperature, the prolongation of the residence time of molten steel in the ladle, the erosion of molten steel and slag on the ladle refractory material, and the chemical erosion of the ladle refractory material by molten slag are all more serious. steel production needs. To this end, a variety of aluminum-magnesium (carbon) ladle refractory materials have been developed successively. During the use of aluminum-magnesium (carbon) refractories, Al2O3 and MgO react at high temperatures to form magnesium-aluminum spinel, a mineral with excellent high-temperature performance, which significantly improves the erosion resistance and spalling resistance of refractories. Therefore, the use of aluminum-magnesium (carbon) ladle refractory materials can greatly increase the service life of the ladle.
Aluminum-magnesium integral ramming material
Aluminum-magnesium ladle overall ramming material. The ramming material uses special-grade high-alumina bauxite clinker as aggregate, and a mixed powder of special-grade high-alumina bauxite clinker powder and sintered magnesia powder as matrix. It is a kind of amorphous refractory material with good plasticity prepared by using liquid water glass as a binder. Used on the 200t steel ladle of A Steel No. 3 Steelmaking, the service life is 5-7 times higher than that of clay bricks, with an average service life of 85.15 times and a maximum of 108 times, and the consumption of refractory materials per ton of steel is 2.7kg. In June 1982, the ramming material passed the identification of the former Ministry of Metallurgy. Afterwards, the ladles of many steelmaking plants successively used this kind of aluminum-magnesium ladle integral ramming material, and all achieved good results.
After aluminum-magnesium ramming materials, aluminum-magnesium castables with high-quality high-alumina bauxite clinker and sintered magnesia as raw materials and liquid water glass as binder have been developed. The castable was first popularized and applied on small ladles, and achieved good results. A steel plant’s 10t and 14t ladles use aluminum-magnesium castables combined with water glass, and the average one-time ladle age is 109.7 times , which is more than 8 times that of clay brick linings. The 15t and 13t ladles of Steel Plant B use aluminum-magnesium castables, and the age of one ladle is 53 times, while the age of clay lining bricks is only 6-10 times.
For medium and small ladles (capacity below 45t) for converters below 30t, most of them use integral casting lining. The life of the overall pouring ladle is mostly 40 to 60 times, and some small ladles can reach 90 times. Refractory material consumption and lining costs have been greatly reduced, and obvious economic benefits have been achieved.
Aluminum-magnesium unfired brick
In addition to aluminum-magnesium ramming materials and aluminum-magnesium castables, aluminum-magnesium unfired bricks combined with water glass have also been developed, which are used on ladles and have a longer life than traditional aluminum silicate ladle bricks. A steel 160t ladle uses aluminum-magnesium unfired bricks, with an average lifespan of 40.56 times, which is more than double that of third-grade high-alumina bricks (lifetime of 18.5 times). The average service life of aluminum-magnesium unfired bricks used in the 20t ladle of Steel Plant B is 38.8 times, and the highest is 55 times, which is more than 4 times the service life of clay lining bricks (9 times).
Magnesium Aluminum Spinel Castable
With the bauxite-based synthesis of magnesium-aluminum spinel, a refractory raw material, has been put into industrial production. A number of refractory research institutions and production enterprises have successively developed a variety of alumina-based magnesium-aluminum spinel castables for ladles with different performance. Since a certain proportion of pre-synthesized magnesium-aluminum spinel is added to this type of castable, the corrosion resistance and peeling resistance of the castable are greatly improved, and its performance is better than that of aluminum-magnesium castables combined with water glass. It has been used on various ladles and achieved good results.
The bauxite-based aluminum-magnesium spinel castables have been tried on a 70t (DH vacuum spray gun blowing argon) ladle of A steel and a 30t continuous casting ladle of B steel (continuous casting ratio not less than 94%), and the average lifespan reaches 71 and 114 times respectively. It is 1-3 times higher than that of aluminum-magnesium castables combined with water glass. A 25t continuous casting (continuous casting ratio greater than 70%) ladle uses magnesium-aluminum spinel castables, with an average ladle age of 77 times, which is 1.2 times higher than that of sodium silicate combined aluminum-magnesium castables. The 28t steel ladle of B Steel Plant uses magnesium-aluminum spinel castables, with an average lifespan of 79 times, which is 1.6 times higher than that of aluminum-magnesium castables combined with water glass.
Bauxite-based magnesia-alumina spinel castable is made of high-quality high-alumina bauxite clinker as aggregate, high-quality high-alumina bauxite clinker powder, synthetic magnesia-alumina spinel powder and sintered magnesia powder as matrix. : Polyphosphate, SiO2 micropowder, Al2O3 micropowder, pure calcium aluminate cement, etc.
Aluminum magnesium carbon brick
The 1990s was a period of rapid development of continuous casting technology, 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 high-efficiency continuous casting technology, aluminum-magnesium-carbon bricks for ladles have been developed, which are used in various continuous casting ladles to greatly increase the service life of ladles.
The aluminum-magnesium-carbon ladle brick is used on the 300t continuous casting ladle of A steel, and the ladle age has increased from more than 20 times when using first-class high-alumina bricks to more than 80 times, with a maximum of 126 times. B Steel No. 3 steelmaking 200t full continuous casting and refining outside the furnace ladle, using 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 in full swing. Many steel mills, according to the actual situation of the enterprise, successively used aluminum-magnesium-carbon steel ladle lining bricks, which significantly increased the life of the steel ladle. For example, A steel 160t ladle used After aluminum-magnesium-carbon lining bricks, the average service life increases to 90 times, and the highest reaches 115 times.
Alumina-magnesia-carbon bricks are non-fired products made of super-grade high-alumina bauxite clinker, fused magnesia or sintered magnesia and graphite, and liquid phenolic resin as a binder. The physical and chemical indicators of aluminum-magnesium-carbon bricks for ladles produced by some manufacturers are shown in Table 5.
|chemical composition / %||Bulk density/g.cm-3||Apparent porosity/ %||Normal temperature compressive strength/ MPa|
Magnesium Aluminum Spinel Carbon Brick
On the basis of the development of aluminum-magnesia-carbon bricks, magnesium-alumina-spinel carbon bricks for ladles were developed. Alumina-magnesia spinel carbon bricks are made by adding a certain proportion of pre-synthesized magnesia-alumina spinel to the bricks, and its performance is better than that of the same grade of alumina-magnesia-carbon bricks.
The magnesia-aluminum spinel carbon brick is used on the A steel 300t continuous casting ladle, with an average service life of 105 times and a maximum of 200 times. Used on the ladle of B steel 200t full continuous casting and refined outside the furnace, the average service life is 73.3 times, and the highest reaches 82 times. Used on the 90t ladle of C Steel No. 2 Steelmaking, the service life is increased from 20 times to 40 times, and the highest reaches 51 times.
The aluminum-magnesium spinel carbon brick further improves the service life of the continuous casting ladle. The physical and chemical indicators of aluminum-magnesium spinel carbon bricks produced by some manufacturers are shown in Table 6.
|chemical composition / %||Bulk density/g.cm-3||Apparent porosity/ %||Normal temperature compressive strength / MPa|
High-grade aluminum-magnesium unfired brick
Carbon-containing ladle lining bricks will cause carbonization of molten steel during use, which is very unfavorable for smelting 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) have been developed. 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.
The use of high-grade aluminum-magnesium unfired bricks on the ladle has achieved good results, and its service life has reached or even exceeded that of carbon-containing ladle lining bricks, while reducing the carbon increase of molten steel. For example, the aluminum-magnesium unfired brick is used on the 100t ladle of A steel plant and the LF refining ladle, and the service life is 1.5 times that of the aluminum-magnesium-carbon brick.
The 200t steel ladle of B steel adopts aluminum-magnesium unfired bricks, and the age of one-time ladle is more than 110 times, and the highest reaches 128 times. The service life of the 170t continuous casting ladle reaches 119 times, which exceeds that of the alumina-magnesia-carbon brick.
High-grade aluminum-magnesium (spinel) castable
High-grade aluminum-magnesium castables are used for large and medium-sized ladles. The raw materials used for high-grade aluminum-magnesium (spinel) castables include corundum (fused corundum, sintered corundum, etc.), high-purity fused magnesia, high-purity aluminum-magnesium spinel (fused and sintered), etc. Binders include pure calcium aluminate cement, Al2O3 micropowder, high-purity SiO2 micropowder, etc.
A steel 300t ladle uses high-grade aluminum-magnesium castables, with an average service life of 258 times. It is used on the 90tLF refining ladle of B Steel Plant, with a service life of 138 times and an erosion rate of 0.62mm/time.
The 200t continuous casting ladle of Plant C uses high-grade aluminum-magnesium (spinel) castables, with a service life of 150 times. Some steel mills have also achieved good results by using castable prefabricated blocks. For example, the service life of C-steel ladle using aluminum-magnesium-carbon bricks is 65 times. After switching to high-grade aluminum-magnesium spinel prefabricated blocks, the average service life increases to 118 times, and the highest reaches 126 times. By 2000, 90% of the steel ladles of C Steel will be lined with high-grade aluminum-magnesium castable prefabricated blocks.
See Table 7 for the physical and chemical indicators of high-grade aluminum-magnesium (spinel) pouring for large ladles in a steel plant.
|chemical composition / %||Bulk density/g.cm-3||Normal temperature compressive strength / MPa||Room temperature flexural strength / MPa||Apparent porosity / %|
Magnesia carbon bricks have excellent corrosion resistance and anti-stripping properties. Magnesia-carbon bricks are mainly used in the slag line on the ladle, and other refractory materials (castables, unfired bricks, etc.) are used in non-slag line parts, so as to obtain a higher service life and reduce the cost of refractory materials.
The No. 2 steelmaking plant of Steel A took the lead in using magnesia-carbon bricks in the 70t ladle slag line, with a service life of 50 times. The high-alumina bricks in the non-slag line were seriously damaged and stopped using. The 300t ladle slag line of B steel began to use MT-14A magnesia carbon bricks, and the life of the slag line was kept at more than 100 times. The 90tLF refining ladle slag line of C steel plant uses magnesia-carbon bricks with a carbon content of about 16%, and the life of the slag line is 95 times. There are also steel mills whose ladles are lined with full magnesia-carbon bricks. For example, a steel plant uses a 60tLF-VD refining ladle for an electric furnace, and is lined with full magnesia-carbon bricks. The average life span is 47 times, and the highest is 57 times.
Low carbon magnesia carbon brick
The use of magnesia carbon bricks in the ladle slag line has the problem of carbon increase in molten steel, and a low carbon ladle slag line magnesia carbon brick has been developed.
A steel 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 use requirements of 300t ladles. The slag line of the B steel ladle also uses low-carbon lining bricks with a carbon content of less than 5%, and the effect is good.
Magnesium-calcium (carbon) ladle refractories
Magnesia-calcium refractories have good high-temperature stability and high-alkalinity slag resistance, especially the free CaO in them can purify molten steel. Therefore, magnesium-calcium refractories are one of the ideal refractories for ladles. As the production of clean steel continues to increase, the application of magnesia-calcium refractories will continue to expand.
Dolomite Ramming Material
Steel A is a dolomite ramming material made of ordinary sintered dolomite as a raw material and medium temperature asphalt as a binder, and is used on a 70t ladle. Good results have been obtained, with an average lifespan of 76 times and a maximum of 112 times.
Unburned magnesia calcium brick
Magnesia-calcium sand and fused magnesia are used as raw materials, and solid inorganic salt and inorganic salt solution are used as binders to develop unfired magnesia-calcium bricks for ladles. Used on the 40tLF-VD refining ladle of S Steel Plant, the service life is more than 40 times, and the oxygen content in the steel drops from 12.2×10-6 to 11.13×10-6.
In recent years, B refractory company has developed anhydrous resin-bonded non-fired magnesia-calcium bricks, which are used in A steel company’s 100tLF refining ladle, with a service life of 80-85 times and an erosion rate of 1.28-1.37mm/time.
Unfired magnesia-calcium bricks are used in the 90tLF refining ladle (refining rate 100%) of A steel plant in the non-slag line part of the cladding wall, and the service life can reach more than 60 times. Due to severe corrosion of the bottom-covered air-permeable bricks, it was discontinued. The thickness of the unfired magnesia-calcium bricks is about 130mm, and they can still be used. It is expected that the normal package life can reach 80-100 times.
Unburned magnesia calcium carbon brick
Using synthetic magnesia-calcium sand, fused magnesia and high-purity graphite as raw materials, and using anhydrous resin as a binder, unburned magnesia-calcium-carbon bricks have been developed. It is used in the non-slag line part of the 225t ladle of the No. 2 steelmaking plant of S Steel (magnesia carbon bricks for the slag line). The average service life is 116.8 times. Compared with the original alumina-magnesia-carbon brick, the average service life is increased by 37.57 times when the cladding wall is thinned by 20mm. And the oxygen content and non-metallic inclusions in the steel are reduced.
|chemical composition / %||Bulk density/g.cm-3||Normal temperature compressive strength / MPa||Room temperature flexural strength / MPa|
The 300t ladle of steel A has used zirconium ladle lining bricks imported from Japan, with an average service life of 90 times. During this period, A refractory material factory produced zirconium ladle lining bricks, which were tested on A steel 300t ladle, and the service life reached 88 times.
To sum up, with the continuous development of steelmaking technology, refractory materials for ladles are also constantly developing. New product varieties are constantly increasing, product quality is constantly improving, and the use effect is getting better and better, which meets the needs of the continuous development of the steelmaking industry. According to the development trend of the steelmaking industry, it is suggested that the development of refractory materials for ladles in the future should be carried out from the following aspects.
(1) Develop refractory materials for ladles with longer service life to meet the needs of efficient continuous casting and refining outside the furnace.
(2) Develop low-carbon, carbon-free and magnesium-calcium ladle refractory materials with better corrosion resistance and spalling resistance to meet the needs of smelting clean steel, low carbon steel and ultra-low carbon steel.
(3) Develop energy-saving refractory materials for ladles, such as unshaped refractory materials and unburned bricks.
(4) Develop resource-saving and environment-friendly refractory materials for ladles.
(5) Carry out research on the reuse of various residual ladle refractories after use.