(1) Chemical attack, including silicon dioxide (SiO2), iron oxide (FeO), and carbon (C).
Since the source molten iron contains a large amount of silicon, it is oxidized to produce acidic oxide silicon dioxide after blowing. When a new furnace is opened for smelting, it takes a certain temperature and time for the lime to melt (melt) into slag. It is difficult for silicon dioxide to be quickly neutralized by lime, and it will follow the molten iron under the agitation of the gas, causing corrosion to the magnesium-calcium material lining, and the reaction produces MgSiO3 and CaSiO3, although MgSiO3 and CaSiO3 are The melting point is above 1550 Celsius and attached to the furnace fire brick to prevent a little corrosion, but the molten iron in the oxidation period contains a lot of FeO, FeO can greatly reduce the melting point of MgSiO3 and CaSiO3, as can be seen in the three series diagram of CaO-SiO2-FeO, Under the action of FeO, the melting point temperature of CaSiO3 can be as low as 1200 Celsius. Because MgO and CaO have very similar chemical and physical properties, MgO and CaO react with silicon dioxide, and the resulting silicate cannot really be attached to the refractory. On the brick, it melts and rises under the action of FeO, and the silicon dioxide continues to react with the furnace lining to corrode the inner lining. From the used magnesium-calcium brick on the left side of Figure 1, the traces of chemical attack can be clearly seen. In addition, near the wind gun eye, due to the vortex action of the molten steel, the chemical reaction heat of the wind gun mouth is quickly applied to the refractory material near the wind gun eye, which has a higher temperature, and the liquid velocity is faster, the flow rate is large, and the contact There is a lot of silica, so the corrosion of the refractory material near the wind gun eye is more obvious. In the furnace in use in Figure 2, it can be seen that the lining near the wind gun eye is obviously sunken.
As the smelting progresses, the temperature of the molten pool rises, and the lime is dissolved (melted) into slag. After the silica is absorbed by the lime, the silicic acid compounds in the molten steel and the slag liquid exist in the form of SiO32- ions, and the chemical equilibrium formula is SiO32- ?SiO2+O2-, therefore, as long as there are SiO32- ions in the molten steel and slag, SiO2 will exist. FeO and SiO2 in the smelting work together to corrode the furnace lining throughout the entire smelting process, increase the alkalinity of the slag, and reduce the smelting time. Controlling the amount of FeO in the slag can slow down the erosion of FeO on the furnace lining.
Due to the high carbon and silicon content of molten iron and high-carbon ferrochromium, the heat is relatively surplus. During the smelting process, the temperature in the furnace quickly rises above 1700. Due to the vortex action of the molten steel near the gun hole, the air muzzle chemical reaction The large amount of heat generated directly follows the vortex of the molten steel and acts on the furnace lining near the air gun eye. The temperature in this area is higher than that of any other parts. The carbon in the molten steel will be reduced to the MgO in the furnace lining as the molten steel washes the furnace lining. Mg volatilizes and corrodes the furnace lining. It can be found from the oxygen potential diagram of the oxide in Figure 4. When the temperature is above 1750, the decomposition free energy of CO begins to be lower than that of MgO, so that the chemical reaction MgO+C=Mg+Co can proceed. , The higher the temperature, the greater the erosion of C to the furnace, another important reason why the erosion near the air gun is faster than other places.
(2) Physical erosion, the solubility of magnesium oxide and calcium oxide in steel is extremely low, which can be ignored. In addition to mechanical erosion and weathering, the physical erosion is the longer the furnace is used, the greater the mechanical erosion and weathering will be, so I won’t discuss it here. In addition, there is another important physical erosion phenomenon: furnace lining fracture and delamination. This discussion only discusses and analyzes the cause of furnace lining fracture and delamination.
The magnesia-calcium fire brick refractories are selected, processed, and press-formed by the machine, and then dried and fired into several stages. There are certain pores on the surface and inside of the brick body. During use, the slag liquid and molten steel will flow into the pores. Infiltration, as can be seen from the two bricks with different porosity in Figure 1, the more the porosity, the more obvious the infiltration. When a certain amount of slag or molten steel penetrates into the brick, the brick body will crack due to the inconsistency of the expansion coefficient of the brick, the slag and the molten steel when the temperature changes greatly. Then it falls off by the scouring action of molten steel, slag and furnace gas. From the furnace in the smelting in Figure 2, it can be seen that the bricks from the top of the air gun to the check line and under the air gun are unevenly broken and fallen off.