In order to meet the needs of the iron and steel industry for multi-furnace continuous casting and energy saving, and to adapt to the more and more severe conditions of use of the furnace refining, domestic and foreign researchers have been committed to the research and development of high-quality, new type, high-efficiency refractory materials, in order to improve the service life of the ladle, which in turn promotes the development of refractory materials for the ladle lining. The development of iron and steel smelting technology to promote the ladle with refractory materials continue to improve and innovate the original reason can be summarized as follows: on the one hand, with the gradual increase in the mechanization of the lining masonry requirements, the lining refractory materials tend to be amorphous; on the other hand, due to the popularity of the second refining and continuous casting, so that the use of the ladle conditions are more stringent, which promotes the lining of the refractory materials to high-purity, high-performance and high-grade direction. Transformation.
Refractories for ladle lining through the changes can be divided into three important time periods:
1.Prior to the 1970s
In Europe and the United States before World War II, the main use of chlorite refractory bricks at high temperatures of the micro-expansion to prevent selective melt damage at the joints of the ladle lining bricks. By the 1950s and 1960s, clay and graphite-clay refractory bricks were widely used in Europe and the United States. Japan in 1960 in yawata company 50t ladle trial stabilized dolomite and tar dolomite refractory bricks, although the life of 70 ~ 100 furnace, but due to the problem of sticking to the ladle has not been popularized, so the development of a more alkaline slag erosion of zirconium silicate refractory materials. At the same time, the lining construction mechanization wave followed. the second half of the 1960s, with the rise of the European throwing process method, adapted to this new construction method of refractory materials have been developed, which is the beginning of the development of refractory materials indeterminate.
Before the seventies, the domestic mainly used clay bricks, ordinary high alumina bricks and semi-silica bricks and other masonry ladle, the average service life of only 10 ~ 40 times or so, and the refractory materials used in a variety of brick type, masonry complicated, material utilization rate of less than 50%. The low service life of the lining material not only causes a large amount of refractory consumption, but also frequent dismantling of the lining, lining has greatly increased the labor intensity of the workers. At the same time, due to a large number of cladding material melt loss of impurities generated by the increase of non-metallic phase inclusions in the liquid steel, resulting in a decline in the rate and quality of steel.
2.1970s-80s
Furnace refining technology began to gradually popularize the application of ladle environment is more and more harsh, the traditional high alumina bricks and high alumina castables began to meet the use of requirements. Europe and the United States researchers to meet the furnace refining on the lining of high purity, alkaline (neutral) needs, to carry out a lot of useful attempts, which is more representative of magnesium-silicon, magnesium-chromium and magnesium oxide – mullite quality of the castables. Finally in the 80’s, researchers figured out the refractory material erosion resistance and the best point of indeterminate shape, the development of aluminum and magnesium castables. At the same time, Japanese researchers try to add zircon as a raw material to the felsite-quality shaped products, research and development of zirconium silicate bricks and a series of ZrO2-Al2O3-SiO2 system of refractories, effectively improving the material’s resistance to slag erosion.
Since the 1970s, the use of refractories for ladle in China has shown diversification and complexity. Among them, China’s independent research and development of high-alumina castables and phosphoric acid as a binding agent of high-alumina pounding material application, greatly improving the service life of small and medium-sized ladle; large ladle more high alumina bricks (its Al2O3 content of 70% ~ 80%) for the inner lining masonry. From the 80’s, with the rapid development of the domestic iron and steel industry, furnace refining and continuous casting and other modern steelmaking technology is gradually mature need to have a higher high temperature strength, slag erosion resistance and thermal shock stability of the package lining refractories. At the end of the 80s, low cement castables became the whole casting method of relying on the beginning of the gradual application of small and medium-sized ladle lining, the average service life of the lining material to 80 times. Al2O3 content in the high alumina bricks used by the steel enterprises will be used in the high alumina bricks to more than 80%, the service life of the ladle has increased exponentially, but due to the relatively poor resistance to slag permeability of high alumina bricks, it is easy to be infiltrated by the slag to form a deterioration of the structural layer and damage due to the structure of the spalling.
3.The 1990s to the present
Since the 90’s, direct bonded magnesium-chromium bricks as well as magnesium-carbon bricks have been used in ladle linings due to their better thermal shock stability and low reaction rate with molten steel. At the same time, corundum-spinel castables have been widely used in ladle working lining, bottom impact zone, etc., and have achieved good results. Europe and Japan use in-situ synthesis technology, the use of alumina and magnesia sand added to the castables in-situ generation of magnesia-aluminum spinel phase instead of pre-synthesized spinel, in-situ generation of fine spinel particles dispersed in the castables matrix, effectively improving the slag encroachment performance of the castables.
In the 1990s, high-efficiency continuous casting technology has become the center of gravity of the development of China’s steel industry, in order to meet the needs of the development of the steelmaking process technology, China will be developed by the development of aluminum-magnesium-carbon bricks put into practical application, greatly improving the anti-erosion of the ladle lining, which in turn improves the service life of the ladle. At the same time, Baosteel in 1994 were introduced into the Japanese production of high-purity aluminum-magnesium quality castables (spinel to the way of in situ generation of the introduction) and European production of corundum – spinel quality castables (spinel to the way of pre-synthesis of the introduction). In the process of comparing and testing the two kinds of imported castables, a whole set of construction, use and maintenance technology of ladle was successfully worked out. in the middle and late 1990’s, on the basis of the existing castables, from the angle of cost reduction, China independently improved and developed high-grade aluminum and magnesium castables and put them into use. In the actual application, it is found that the high-grade aluminum and magnesium castables have reached the world’s leading level no matter in the construction performance, service life or cost per ton of steel.
Nowadays, the research and application of refractories for ladle lining mainly focus on Al2O3-MgO-CaO system, which is different from the shaped products with various brick shapes, complicated masonry and difficult repair, and the Al2O3-MgO-CaO system of castables obtained by adding ultra-fine powder or adopting high-purity raw materials has excellent and balanced performances, which greatly improves the service life of ladle.
4.Causes of damage to ladle linings
With the improvement of steelmaking technology and the diversification of ladle refining technology, due to the influence of factors such as the increase of liquid steel temperature, the prolongation of residence time and the vacuum refining environment, the use of the ladle environment is more and more demanding, which seriously affects the service life of the ladle lining and production efficiency. The causes of damage to ladle liners are mainly divided into the following three categories:
(1)Thermal spalling
The on-line baking temperature of the ladle is about 800~1000℃, while the temperature range of the steel output from the converter and electric furnace is 1600~1700℃, with a maximum temperature difference of up to 900℃. Therefore, the intermittent operation of the ladle, as well as the rapid cold and heat shock in repeated use, makes the thermal stresses due to temperature changes between the working surface of the cladding lining working layer (in direct contact with high temperature molten steel) and the non-working surface, or between the components with different coefficients of thermal expansion inherent in the material, or between the original brick layer and the metamorphic layer resulting from the penetration of the slag and other erosion agents into the pores inside the refractory material; some of the No burn or low temperature baking lining working layer material, in the process of using the material internal mineral phase transformation, phase change stress. If the thermal stress, phase change stress exceeds its use strength, resulting in spalling damage.
(2)Mechanical damage
Out of the steel, steel on the lining of high-speed, strong scouring, or refining into the gas, gas and liquid steel two dispersion system to intensify the movement between the formation of turbulence, the scouring of the ladle lining and abrasion, and so on, these mechanical stresses caused by the ladle lining of the mechanical damage.
(3)Chemical erosion
In the whole process of ladle service, due to the high temperature steel, slag and ladle lining for a long time in contact with the slag and other erosive agents will continue to the lining of the working layer of immersion. Steel and slag oxides (CaO, FeO, Fe2O3, MnO, SiO2, etc.) and ladle lining chemical reactions occur as follows:
312CaO+7Al2O3=12CaO·7Al2O3
FeO+Al2O3=FeO·Al2O3
2MnO+SiO2+Al2O3=2(MnO)·SiO2·Al2O3
The chemical erosion and infiltration of low melts such as 12CaO-7Al2O3, FeO-Al2O3, 2(MnO)-SiO2-Al2O3, etc., which are generated by the reaction, lead to the deterioration of the working surface, which in turn reduces the service life of the ladle lining.
