AOD refractory for furnace

With the development of iron and steel metallurgy technology, the market competition intensifies, and the demand for high quality steel is more and more high. In order to adapt to the development of clean steel and meet the requirements of users, the proportion of refining outside the furnace is increasing. Therefore, the proportion of refractories for refining out of furnace that meet the requirements of clean steel production is higher and higher.

The world's first AOD furnace was built in October 1967 by Joslyn Stainless Steel. At the beginning of oxygen blowing oxidation and decarburization, during the oxidation period, the oxidation property of the slag was enhanced and the temperature rose to 1700℃. Then enter the reduction stage, add ferrosilicon or aluminum, make the chromium reduction in the slag, in order to improve the alloy yield, at this time the slag basicity is still very low; Finally, lime desulfurization requires high alkalinity slag. During the whole smelting process, the slag changes from acid to alkaline. The atmosphere also changes from oxidizing atmosphere to reducing atmosphere. Then intermittent operation, lining temperature is high and the fluctuation is quite large. Therefore, AOD lining service life is very low. Before, the service life of AOD furnace was only about 30 furnaces. By improving smelting conditions and adopting measures such as spraying and maintenance, the service life of AOD furnace generally reached more than 70 furnaces, many of which exceeded 100 furnaces. For AOD furnaces, magnesia-chrome brick is generally used. Due to the complex production process of magnesia-Chrome brick, high energy consumption and high cost, especially the environmental pollution problem, magnesia-Chrome brick is gradually replaced by magnesia-calcium brick.

Causes of damage of AOD lining :(1) melting and penetration of lining due to high smelting temperature and long acting time of acid slag; (2) Temperature fluctuation caused thermal spalling and structural spalling; (3) Intense gas-slag-molten steel eddy current erosion and scouring; (4) Under the change of AOD atmosphere, the REDOX reaction of Cr2O3 and FeOn in magnesia-Chrome brick occurred, which destroyed the structure and volume stability of the brick and accelerated the abrasion.

The tuyere position is mainly thermal flaking and structural flaking. The erosion around tuyere is mainly caused by eddy currents and low alkalinity slag. The structure of the slag line is mainly exfoliated by the high alkalinity slag. The bottom of the furnace is mainly eroded and permeated by high alkalinity slag. Therefore, the requirements for magnesia-Chrome brick are low porosity, high temperature strength, high thermal shock stability and high slag permeability.

Factors influencing the life of lining refractories

The results show that :(1) the corrosion amount of magnesia-chrome brick increases with the increase of the alkalinity of the slag. The slag basicity (CaO+MgO) /(SiO2+Al2O3)=1.2~1.5 can obtain a higher life; (2) With the increase of MgO, Cr2O3, Al2O3 and other contents in the slag, the erosion of magnesia-Chrome brick decreases; (3) The reducing agent is easy to REDOX with Cr2O3 and FeOn in magnesia-Chrome brick, which destroys the structure of the brick, and the neighboring particles will be washed away, which also makes the chromium in the molten steel difficult to be controlled. (4) When smelting Al/Si killed steel, the damage degree of Si killed steel and Al killed steel to refractory materials decreases successively. Silicon and manganese in alloy steel can increase the corrosion of refractory lining. (5) Between 1600 and 1750℃, the dissolution rate of mg-Cr material increases 4-5 times and mg-Ca material increases 2-3 times with every 100℃ increase of temperature. (6) Magnesia-Chrome brick is affected by the atmosphere, which will easily lead to the change of chromium and iron in the bricks and produce a large volume effect, resulting in the destruction of the brick structure; (7) Fluorite and Al2O3 in the slag interact with magnesium-Calcium material to form low viscosity and low melting point eutectic, which accelerates the erosion; (8) Mgo-based materials have stronger corrosion resistance to low alkalinity slag than mgo-based materials, while mGO-based materials have stronger corrosion resistance to high Al2O3 or high iron slag than Mgo-based materials. CaO is more resistant to high phosphorus slag than MgO. (9) The blowing Angle has a great influence on the erosion. Generally, the backhand inclination Angle is 5°~7°. (10) For low alkalinity slag, magnesia-Chrome brick is more resistant to erosion than magnesia-calcium brick; (11) The dissolution rate of mG-Cr and Mg-CA in acid slag is directly proportional to the 0.7 th power of rotating speed.

At present, the development trend is less and less magnesia-Chrome brick. It is worth pointing out that when smelting temperature is very high, carbon-containing refractory materials are not suitable for internal REDOX reaction. Apply magnesia-chrome brick or magnesia-calcium brick to go.