Induction Furnace Refractory Material
Induction furnace steelmaking methods are divided into acid smelting and alkaline smelting methods according to the properties of refractory materials.
Acid slag is produced during smelting by the acid smelting method. Therefore, refractory materials are mainly quartz sand and zircon, and their knotting, baking, and sintering processes are similar to those of smelting cast iron. Quartz sand or zircon sand furnace lining is generally used for the smelting of low-carbon steel or low-alloy steel.
Alkaline smelting produces alkaline slag during smelting, so the refractory materials are neutral, alkaline refractory materials or graphite crucibles, which are suitable for smelting high-alloy steel, special steel, precision alloy steel, and other steel types. Historically, there are Multiple series of refractory materials are used in the lining of induction furnaces, among which SiO2 and zircon have been used occasionally due to acidity, and have continued to this day, but the more popular refractory materials for induction furnace steelmaking are mainly high alumina, MgO—CaO Quality and refractory materials composed of Spinel.
Due to the diversification of functions, the induction furnace needs a variety of high-performance refractory materials to adapt to it. That is to say, the application of refractory materials such as high alumina bricks in induction furnaces not only needs to consider the furnace type, furnace body structure, and smelting process, but also the material of refractory materials and their mineral phases from normal temperature to working temperature. 1. The change process and change mechanism of physical properties: at the same time, the selection of refractory materials and the improvement of material properties should be carried out according to the application requirements, especially the application requirements of innovative equipment.
When the acid steelmaking method is used, since acid slag is produced during smelting, the lining of the coreless induction furnace is mainly made of quartz sand (sometimes zircon is also used), and its lining method, baking system, and sintering process are similar to those of cast iron smelting. almost the same.
When steelmaking is made by the basic steelmaking method, neutral or basic refractory materials and graphite crucible are used for lining. This smelting method is mainly suitable for high alloy steel, special steel, precision alloy steel, etc.
In alkaline steelmaking, due to the addition of lime, fluorite, and various ferroalloys (ferrosilicon, ferromanganese, ferrochrome, and ferromolybdenum, etc.), compared with smelted cast iron, the composition of slag is complex, the wettability is large, and the smelting temperature is high. Serious erosion of refractory materials. Among them, small induction furnaces are generally lined with magnesia refractory materials.
However, due to the large expansion coefficient of MgO, poor thermal shock resistance, and the problem that it is easily penetrated by slag, resulting in structural spalling, it is not suitable for the use conditions of large-capacity, intermittently operated induction furnaces. In order to be able to adapt to the use conditions of large-capacity and intermittently operated induction furnaces, an appropriate amount of AL2O3 fine powder can be added to magnesia, and the reaction: MgO + AL2O3 → MgO · AL2O3 (Spinel) can be used to generate Spinel to inhibit cracking.
Or use MgO-Spinel dry-type binder, use the low thermal expansion of Spinel to buffer high-temperature stress, and improve the thermal shock resistance of the inner lining. Such MgO + AL2O3 or MgO-Spinel refractories belong to the MgO – AL2O3 system.
After these mixtures are heated at high temperatures, their mineral phases are periclase and spinel, and above 2050°C, they are periclase and liquid phase, so they have excellent high-temperature performance.
Today, as steelmaking application furnaces are becoming larger and more powerful, the focus is on using Al2O3-based refractory materials and improving their performance as much as possible. Due to the aggressive environment and extremely severe thermal shock conditions of the "batch smelting" (using direct reduced iron balls as additives, etc.) coreless induction furnaces, it is necessary to add MgO and chromium ore (Cr2O3 powder) to the AL2O3-based refractory material And with Synthetic Spinel et al. to optimize material properties.
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