What refractory bricks are suitable for making hot metal ditch refractory factory facing the increasing demand for iron and steel in the present society, along with the large-scale production equipment, the blast furnace tapping temperature increases, the amount of iron tapping increases, and the tapping time prolongs. Therefore, the use conditions of hot metal ditch in blast furnace are very harsh. The traditional refractories for tapping ditches are replaced by corundum, silicon carbide, graphite and other materials. In order to satisfy the use of refractory bricks in hot water ditch of blast furnace, Zhengzhou Juda Refractories Co., Ltd. has trial-produced high alumina silicon carbide bricks through analysis and comparison.

High-alumina bricks were used in hot metal ditch firebricks before, but it was found that the corrosion of high-alumina bricks was related to C in molten iron. On this basis, the corrosion process of high-alumina bricks was analyzed. The influence of C content in molten iron on the corrosion of bricks was analyzed. It was found that the damaged high-alumina bricks could be roughly divided into three layers, the surface layer was molten iron adhesive layer, and the inner layer was original brick layer, and the porous layer was about 2 mm thick between the two layers. Metamorphic layer. The main phase of the metamorphic layer is crystalline less than 100 microns, and there are a large number of pores larger than 100 microns remaining in the microstructure, but no Fe is observed. From the interface between metamorphic layer and original brick, it can be seen that the original brick is AL2O3-SiO2, that is, mullite particles. The columnar particles with a length of 100 um in the metamorphic layer are corundum, and the compositions between the columnar particles are found to be AL2O3-SiO 2-FeO glass phase. It can be judged that these components are formed by the reaction of mullite aggregate with molten steel during erosion. The occurrence of this phenomenon is related to whether there is C in molten iron. That is to say, if there is C in molten iron, the glass phase of AL2O3-SiO2-FeO system will disappear in the reduction of SiO2, while FeO will also be reduced to metal Fe, and the remaining AL2O3 will be precipitated as corundum crystal. Based on the analysis of the corrosion test results of high alumina brick and molten iron, the following conclusions can be drawn: after 5 hours of contact between high alumina brick and molten iron at 1650 C, a metamorphic layer is formed on the surface of the brick. The metamorphic layer consists of corundum particles and SiO_2-ALO_3-FeO glass phase filled between the particles. When high alumina brick is eroded by molten iron without C, the mullite aggregate dissolves to form SiO-ALO-FeO glass phase. When C is contained in water, the glass phase is reduced by C to form corundum and metal Fe. Therefore, the effect of C element in molten iron on the corrosion of high-alumina bricks shortens the service life of high-alumina bricks.

We have produced high alumina SiC brick through another experiment. The first grade high alumina bauxite clinker, silica carbide sand and SiC powder with 94% lime corundum and SiC content are selected as raw materials. Pulp waste liquor was selected as binder. In order to prevent the oxidation of silicon carbide, three different oxidants were selected and achieved certain results.

According to the requirement of refractories in hot metal ditches, high alumina silicon carbide bricks should have good thermal shock stability, sand erosion resistance and corrosion resistance. About 80% of the bricks have a single weight of more than 50 Kg, so the limit size of particles should be appropriately enlarged. This is beneficial to the thermal stability, sand resistance and erosion resistance of bricks. The particle limit size of the batch is 4 mm. The particle composition of various raw materials is shown in the table below.

According to the proportion of various raw materials, the raw materials are mixed in the sand mixer. In order to distribute the antioxidant and other additives evenly in the matrix, the pre-mixing process was adopted. The feeding sequence is as follows: first adding high aluminium clinker, brown corundum, SiC sand, dry mixing for 5 minutes, then adding pulp waste liquid, wet mixing for 2 minutes, then adding mixed fine powder, mixing for 15 minutes, then discharging, totally mixing for 22 minutes. Then, in 1000 ton mechanical press, the density of high alumina SiC bricks is 2.76g/cm 3 and 2.75g/cm 3 respectively. Sintering of high alumina SiC bricks at low temperature stage, in order to avoid cracking caused by excessive removal of residual moisture in the body, it is necessary to raise the temperature slowly and the heating rate is 15-20 C/h. The temperature can be raised freely in the middle temperature stage. The final sintering temperature is 1430 C, holding for 36 hours, the oxide layer thickness of the product, the surface low melt content is greatly reduced, and fully sintered.

High alumina silicon carbide bricks produced by using first-grade bauxite clinker, brown corundum and silicon carbide as raw materials and a small amount of auxiliary materials have achieved good results in the application of hot water ditch and can be used continually.