The principles and functions of electric furnaces, AOD furnaces, LF furnaces, and VD vacuum furnaces

Electric stove

The electric furnace steelmaking method mainly uses arc heat. In the arc action area, the temperature is as high as 4000°C. The smelting process is generally divided into a melting period, an oxidation period and a reduction period. Not only an oxidizing atmosphere but also a reducing atmosphere can be created in the furnace, so the efficiency of dephosphorization and desulfurization is very high.

Electric furnace steelmaking using scrap steel as raw material requires less infrastructure investment than the blast furnace converter method. At the same time, due to the development of direct reduction, metallized pellets are provided for the electric furnace to replace most of the scrap steel, thus greatly promoting electric furnace steelmaking.

Function: At present, there are many intermediate frequency furnaces in China, which are mainly used for smelting high-quality steel, alloy steel and stainless steel. It is the first production process for smelting stainless steel. Its main function is to melt the molten steel and dephosphorize and desulfurize it.

AOD furnace

The AOD furnace method (argon oxygen decarburization method) is the most advanced technology for refining stainless steel. It has the advantages of simple equipment, convenient operation, strong adaptability, low investment, and low production cost, and is widely used.

The molten iron in the blast furnace and the molten steel melted in the electric furnace are injected into the AOD furnace through the ladle. During smelting, O2, Ar or N2 mixed gas is blown into the molten steel to decarbonize the molten steel. At the same time, the feeding system adds reducing agent, desulfurizer, ferroalloy or coolant to adjust the composition and temperature of the molten steel to smelt qualified stainless steel materials.

Principle: The transportation and adjustment of mixed gas during refining is one of the main systems of the argon-oxygen furnace. The gas produced in the oxygen production workshop is transported to the gas storage tank near the workshop through pipelines. After metering, decompression, adjustment and mixing, the mixed gas according to the flow rate and proportion required by the process is finally sent into the furnace through the side gun.

At the beginning of smelting, oxygen is blown into the metal molten pool from the top furnace mouth through a double-layer water-cooled oxygen blowing pipe for decarburization. During refining, the mixed gas is fed into the side gun into the furnace (installed on the side wall opposite the tapping port and close to the furnace bottom). When charging and tapping steel, the furnace body tilts forward at a certain angle, and the (side) tuyere is above the liquid steel level. During normal blowing, the tuyere sinks into the depth of the melting pool. The central tube of the tuyere blows into the mixed gas of oxygen and argon or nitrogen. By adjusting the ratio of oxygen to argon, the partial pressure of carbon monoxide can be reduced to achieve the purpose of decarburization and chromium preservation. The type of tuyere of AOD furnace is unique. It is a consumable tuyere that is cooled by gas. The tuyere adopts a double-layer casing structure. The outer tube only passes argon or nitrogen to cool the tuyere, and the inner tube passes a mixed gas of oxygen and nitrogen, or argon. To achieve the best operating effect through the flow control of the air mask ring, the flow rate of the central tube of the air mask ring and the air mask ring can be controlled in the main control room.

Using three side gun technology. It can enhance the oxygen supply intensity and increase the metal material yield. This technology can shorten the AOD smelting time. A stable and reliable control system can reduce the consumption of gas and various raw materials in smelting and obtain stable product quality.

Function: The main function of AOD is to remove carbon and play a refining role.

LF furnace

LF furnace (LADLE FURNACE) is a ladle refining furnace and is the main out-of-furnace refining equipment in steel production. LF furnace generally refers to the refining furnace in the steel industry. It is actually a special form of electric arc furnace.

LF furnace refining mainly relies on white slag in the barrel. In a low-oxygen atmosphere (oxygen content is 5%), argon gas is blown into the barrel for stirring, and graphite electrodes are used to heat the molten steel that has passed through the primary refining furnace for refining. Since argon stirring accelerates the chemical reaction between slag and steel, using arc heating for temperature compensation can ensure a longer refining time. This can reduce the oxygen and sulfur content in the steel, and the inclusions are rated 0 to 0.1 according to ASTM. The LF furnace can be matched with the electric furnace to replace the reduction period of the electric furnace, and can also be matched with the oxygen converter to produce high-quality alloy steel. In addition, the LF furnace is also an indispensable device for controlling the composition, temperature and preserving molten steel in the continuous casting workshop, especially in the alloy steel continuous casting production line. Therefore, the emergence of LF furnace formed a new joint production line of LD-LF-RH-CC (continuous casting) for the production of high-quality steel. The reduction and refining of steel in this joint production line is mainly completed by the LF furnace. The steel types processed by the LF furnace involve almost all steel types from special steel to ordinary steel. Different process operating systems are adopted depending on the needs of quality control during production. Among various secondary refining equipment, the LF furnace has the highest overall cost performance.

LF has the following characteristics:

①Desulfurization

②Temperature adjustment

③Precise ingredient fine-tuning

④Improve the purity of molten steel

⑤Slag making

It mainly has the following functions:

(1) The LF furnace is connected to the electric furnace, which speeds up the production cycle of the electric furnace and improves the quality of electric furnace steel.

(2) The LF furnace is connected to the LD converter, which can reduce and refine the converter steel, so it can improve the quality of the steel and produce new steel types.

(3) The LF furnace can strictly adjust the composition and temperature of molten steel, which is beneficial to the hardenability of steel and the continuous casting of special steel.

After refining by AOD, it is refined in the LF furnace, which is a secondary refining. The inclusions are reduced to ensure the purity of the molten steel;

VD vacuum furnace

The VD refining method is a vacuum treatment method for molten steel in which the primary molten steel from electric furnaces and converters is placed in a sealed tank to evacuate, while argon is blown at the bottom of the ladle for stirring. After melting and preliminary blowing in electric furnaces and converters, it is then placed in a vacuum tank (vacuum chamber) and stirred by bottom-blown argon and vacuum degassing to obtain pure molten steel.

The VD furnace generally matches the LF furnace. The composition and temperature adjustment are completed by the LF furnace, while degassing, stirring and other tasks are completed by the VD furnace. There is also an oxygen gun installed on the vacuum cover of the VD furnace to smelt stainless steel, which is called a VOD furnace.

Function: The VD furnace is a widely used vacuum refining equipment with good degassing and deoxidation effects. It can effectively reduce the hydrogen and nitrogen content in steel, remove oxygen from steel through the reaction of carbon and oxygen, and desulfurize through the full reaction of alkaline top slag and molten steel. In addition, it also has the function of uniform composition and temperature.