The blast furnace iron ditch is a channel for guiding high-temperature molten iron and molten slag, and its refractory lining is subject to high temperature, mechanical and chemical erosion of molten iron and slag. The first is the scouring effect of iron and slag on the surface of the refractory material when the iron and slag flow; the second is due to the frequent alternation of cold and heat during tapping or the long-term action of high temperature, the refractory material produces microcracks. Such microcracks promote the penetration and structural damage of molten iron and slag. Therefore, the iron trench lining material is required to have strong scour resistance of molten iron and slag; good thermal expansion stability; small change in reburned volume; strong oxidation resistance; Uniform, high-density structure, high strength; no slag iron, no harmful gas, conducive to environmental protection.

After the blast furnace was enlarged, the use conditions of the tapping ditch also changed. The scouring and wear of the ditch wall by molten iron increased, increasing the age of the ditch, reducing the cost, and reducing the work pressure of the workers behind the furnace. These are the main goals of the post-furnace work. For the main groove and different parts, the erosion conditions are different, and the selection of materials should be different to achieve a comprehensive and balanced economic life; for iron grooves, efforts should be made to improve the anti-penetration performance of the material. In terms of construction technology and maintenance process, some operation methods are also closely related to the service life of materials.

A. Damage mechanism of blast furnace iron trench refractory

The damage of refractory materials for blast furnace iron trenches is mainly caused by cracks and chemical erosion, penetration and erosion damage caused by thermal shock of high temperature molten iron and slag.

The first is the effect of high-temperature molten iron. Due to the pressure of the blast furnace, the molten iron of up to 1500°C gushing out of the blast furnace directly impacts the working face of the iron trench, causing erosion and damage to the trench lining material, especially in the impact area. The eddy current formed here not only aggravates the thermal shock effect of molten iron and molten slag on the groove lining, but also aggravates the erosion and erosion damage of the groove lining, and the damage to the groove lining material is the most serious. service life of the trench.

Secondly, in the metallurgical industry, the damage of slag to refractory materials is the most serious. Because the slag contains relatively complex chemical components, it is easy to react with the components in the refractory material to form a low melting point substance, which will cause the damage of the refractory material structure and reduce the corrosion resistance and erosion resistance of the refractory material. When the blast furnace is tapping, in addition to the high-temperature molten iron, there is also high-temperature molten slag in the tapping trench. The slag buildup not only aggravates the erosion of the trench lining, but also tends to adhere to the trench wall, which is the main factor to damage the trench lining material. In addition, the damage to the trench lining material by melting and fishing also varies according to the structure of the iron tapping trench. For the iron-holding type tap trench, the damage of slag is mainly scouring and erosion, while for the non-iron-holding type tap trench, in addition to the above effects, more and more deposition of slag adhering to the trench wall hinders the For the normal use of the tap ditch, therefore, the slag removal operation must be carried out before the furnace. At the same time as the slag removal is performed, the refractory material on the ditch wall will be removed together with the bonded slag. The biggest damage to the lining.

Third, although the blast furnace is a high-temperature equipment that operates continuously, the tapping is an intermittent operation, which causes the trench lining refractory to undergo rapid changes in temperature (at this point, the iron-containing type tapping trench is also more efficient than the non-iron-containing type. The tapping groove has an advantage), so the rapid temperature change reduces the thermal shock stability of the groove lining refractory.

In addition to the above damage, the penetration of molten iron to the trench lining material is also one of the factors that destroy the material structure, which causes the material to erode and peel off, thereby reducing the erosion resistance.

B. Ferrosilicon nitride applied to Al2O3-SiC-C blast furnace castables

Before the 1960s, Tiegou of medium and small blast furnaces were mainly made of coke, clay clinker and clay, and artificial ramming materials stirred with tar or syrup, which were manufactured by iron factories themselves. The service life of this kind of iron groove lining is short, and the iron flux is less than 10,000 tons. In the long-term production practice, people gradually realized that adding silicon carbide and graphite can significantly improve the service life of the tapping groove. In terms of refractory aggregates, corundum, high alumina vanadium, and magnesia-aluminum spinel were tested. In terms of binders, various iron grooving materials of resin-bonded, cement-bonded and clay-bonded were tested. After continuous attempts, various types of iron ditch materials suitable for large, medium and small blast furnaces have been gradually formed. For high-temperature and high-pressure operation, it has large tapping volume, fast flow rate, high temperature (1500°C) method, frequent tapping times, long time, large slag volume, and poor service conditions for tapping trench lining materials. To this end, a new generation of iron channel material mainly composed of Al2O3-SiC-C has been developed, which basically meets the requirements of production, and the iron throughput is from tens of thousands of tons to 100,000 tons.

Al2O3-SiC-C castables have good slag corrosion resistance and scour resistance, and have been widely used in the main trench, slag skimmer and branch trench of blast furnace tapping trenches. However, due to the development of smelting technology, the continuous improvement of blast furnace utilization factor and the requirement of blast furnace longevity, it is urgent to further improve the life of Al2O3-SiC-C castables for iron trenches. However, the current Al2O3-SiC-C castables for iron trenches are prone to fall off under the action of periodic slag, chemical erosion of molten iron, thermal shock, and slag and iron scouring; at the same time, silicon carbide and carbon in the iron trench castables The oxidation of the material at high temperature will also cause the structural damage of the material, which will lead to the damage of the castable for the iron trench.

In recent years, the research on the use of ferrosilicon in Al2O3-SiC-C castables for iron trenches has been increasing. Si3N4 in ferrosilicon nitride has the advantage of not being completely wetted with slag and iron, which can improve the corrosion resistance of iron trench castables; the oxidation products of Si3N4 will form a SiO2 protective film on the surface of the sample, hindering further oxidation of the material , enhance its anti-oxidation performance; the metal phase Fe has the effect of sintering aid, which can improve the mechanical properties of the castable. Under the high temperature oxidizing atmosphere, Si3N4 in the surface ferrosilicon nitride is first oxidized to form SiO2, which constitutes the main body of the oxide layer; with the oxidation of the iron phase material, the formed iron oxide (FexO) reduces the melting point of the oxide layer and the viscosity of the melt , promotes the wettability and fluidity of the melt on the surface of the castable, forms an oxide layer covering the surface of the castable and prevents the oxidation of the carbon material, making it better than pure Si3N4. Fe in the material does not exist in the form of iron oxide (FexO), which is not harmful to high temperature performance. At the same time, the N2 generated by the oxidation of Si3N4 in the ferrosilicon nitride at high temperature and the CO generated by the oxidation of the carbon material will block the internal pores of the material, thereby effectively preventing further oxidation.