Induction furnace in steel plant is a steelmaking method that uses induction electrothermal effect to heat and melt metal. It’s especially suitable for smelting a small amount of high-quality steel and alloy with high-quality raw materials (high-quality scrap steel, ferroalloy, etc.). A vacuum induction furnaces equipped with a vacuum system is an important equipment for smelting high-quality alloys.
Features
Induction Furnace In Steel Plant Features
There are two types of induction furnaces: melting ditch type and crucible type, and their working principle is similar to that of transformers.
The primary winding (induction coil) of the melting groove induction furnace is equipped with an iron core to reduce magnetic flux leakage and improve the power factor. The secondary winding is a melting groove filled with molten metal. When alternating current is passed through the induction coil, an induced electromotive force is generated in the liquid metal in the melting ditch, which generates Joule heat and heats the charge. Therefore, the melting ditch is always filled with molten metal, and the furnace cannot be stopped arbitrarily, and it is not appropriate to frequently change the type of smelted metal. At the same time, the energy is converted in the melting ditch and then transmitted to the molten pool, and the heat load of the melting ditch is very high, so although the power factor and electrical efficiency of this induction furnace are high, it’s not suitable for melting alloy steel and alloy.
The crucible type induction furnace is to place the crucible in the induction coil. When the alternating current is passed through the induction coil, an induced electromotive force is generated in the charge in the crucible, and then Joule heat is generated to melt the charge. The power factor and thermal efficiency of the crucible induction furnace are low, but it can smelt high melting point metals, and it is easy to change the type of smelting.
Induction Furnace in Steel Plant Process
Induction furnace in steel plant, desulphurization and deoxidation are carried out at the same time. Generally, decarburization and dephosphorization are not carried out. Therefore, good raw materials must be selected and melted as soon as possible. The temperature is suitable for deoxidation and tapping.
Feed
In addition to meeting the requirements of chemical composition, the scrap steel and return charge used should also have appropriate dimensions so that the charge can be heated effectively. For this reason, some scraps can also be used to fill the gaps to improve the density of the charge in the crucible. When a molten pool is formed at the bottom of the crucible, the size of the charge has no effect on the heating effect.
Since there is no oxidation period during smelting, the element burning loss is very small, and accurate batching can be achieved. Alloys that are not easily oxidized, such as nickel, molybdenum iron, etc., can be added at the same time as scrap steel.
In order to improve the productivity, reduce the hydrogen content in the steel, and avoid the explosion of the scrap steel containing moisture or grease when heated in the furnace, the scrap steel can be preheated to below 550 °C. If the preheating temperature is too high, the charge will be seriously oxidized and the thermal efficiency will be reduced.
In discontinuous steelmaking, wet material and oil-containing material must be added in the first batch for drying, and only dry material can be added after the molten pool is formed. Small furnaces are generally charged by hand, using boxes or chutes to load the furnace into the furnace. Large furnaces can be loaded with conveyor belts or baskets.
Melt
Pay close attention to the melting of the charge, continuously feed and loosen the charge in a timely and continuous manner, so that it can smoothly descend into the molten pool, keep the melting forward, and avoid bridging.
The so-called “bridging” is that the charge in the semi-molten state sticks above the molten pool so that the charge cannot contact the molten pool. This can cause a sharp rise in the temperature of the molten pool, damaging the crucible. Once the bridging occurs, the crucible can be tilted to melt the gap on the erected charge, so that the charging can be continued, and the molten steel surface can be raised to the bridge to melt the debonded charge.
Slag
Slag formation should be carried out before all the charge is melted to avoid serious oxidation of molten steel. Slag can be added to the bottom of the crucible in advance.
The slag used is mainly CaO-Al2O3-CaF2, and the composition of the slag varies according to different crucible materials and deoxidizers. The slag should be pre-dried to prevent the molten steel from increasing hydrogen.
Slag Removal, Deoxidation, Tapping
After the charge is fully melted, the temperature is measured and sampled, and skilled operators can coordinate the pre-furnace operation by adjusting the input power and correctly predicting the time for the temperature to rise to the tapping temperature. According to the analysis result of the steel sample before the furnace, the alloy material is mixed and deoxidized with ferrosilicon powder and various composite deoxidizers at the same time.
Due to the strong stirring of the molten pool, the alloy material can be rapidly melted and evenly distributed, and the deoxidized product can also float up and be adsorbed by the molten slag. After the ingredients are qualified and the temperature is suitable, the slag can be removed.
If the molten slag is thin, you can pour out the crucible or add lime, and remove it after the slag is thickened. When tapping, add 1-2kg/t aluminum or other strong deoxidizer to the steel stream for final deoxidation.
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