What are the Characteristics of Electric Arc Furnace Steelmaking?

Characteristics of electric arc furnace: An electric furnace that uses the high temperature generated by the electrode arc to melt ores and metals. When the gas discharge forms an arc, the energy is very concentrated, and the temperature in the arc zone is above 3000℃. For smelting metals, electric arc furnaces have greater process flexibility than other steelmaking furnaces, can effectively remove impurities such as sulfur and phosphorus, the furnace temperature is easy to control, the equipment occupies a small area, and is suitable for the smelting of high-quality alloy steel.

Electric arc furnaces can be divided into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces and submerged electric arc furnaces according to the arc form.

The furnace body of the electric arc steelmaking furnace consists of a furnace cover, a furnace door, a steel tapping trough and a furnace body, and the furnace bottom and furnace wall are built with alkaline refractory materials or acidic refractory materials. Electric arc steelmaking furnaces are divided into ordinary power electric arc furnaces, high power electric arc furnaces and ultra-high power electric arc furnaces according to the transformer capacity per ton of furnace capacity. Electric arc furnace steelmaking is to input electric energy into the electric arc steelmaking furnace through graphite electrodes, and use the arc generated between the electrode end and the charge as the heat source for steelmaking.

Electric arc furnace uses electric energy as the heat source, which can adjust the atmosphere in the furnace, which is extremely beneficial for smelting steel containing more easily oxidized elements. Soon after the invention of electric arc furnace steelmaking, it was used to smelt alloy steel and has been greatly developed.

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

Steelmaking process using electricity as energy.

This type of steelmaking furnace, namely electric furnace, includes electric arc furnace, induction furnace, electric slag furnace, electron beam furnace, consumable arc furnace, etc. Electric furnace steel is usually called steel produced by alkaline electric arc furnace.

Electric furnace steel is mostly used to produce high-quality carbon structural steel, tool steel and alloy steel. This type of steel has excellent quality and uniform performance. At the same carbon content, the strength and plasticity of electric furnace steel are better than those of open-hearth steel. Electric furnace steel uses similar steel scrap as the main raw material, and sponge iron is also used to replace part of the scrap steel. The chemical composition and alloy element content are adjusted by adding ferroalloys.

Compared with the blast furnace converter method, electric furnace steelmaking using scrap steel as raw material requires less infrastructure investment. At the same time, due to the development of direct reduction, metallized pellets are provided for electric furnaces to replace most of the scrap steel, which greatly promotes electric furnace steelmaking. There are about 1,400 larger electric furnaces in the world. At present, electric furnaces are developing towards large-scale, ultra-high power and electronic computer automatic control. The maximum electric furnace capacity is 400 tons.

Foreign electric furnaces above 150 tons are almost all used to smelt ordinary steel. In many countries, 60% to 80% of electric furnace steel production is low-carbon steel. Due to the shortage of electricity and scrap steel in my country, it is currently mainly used to smelt high-quality steel and alloy steel.

Short process technology is relative to the traditional long process (academically called traditional process). The traditional long process refers to the blast furnace-converter-continuous casting (or mold casting) process.
The electric furnace short process is represented by the electric furnace-thin slab continuous casting process in the United States in the early 1990s. Since the process was put into production, it has attracted the attention of the world's steel industry. The compact electric furnace short process is a typical representative of the electric furnace short process.

Compared with the traditional process, the electric furnace short process has the following characteristics:

1) The investment is reduced by more than 1/2 compared with the blast furnace-converter process. For example, the electric furnace steelmaking thin slab electric furnace short process in the United States, Japan and other countries has an actual cost of about 1/4 of the traditional process.

2) Low production cost and high labor productivity. From iron-coke-burning to hot-rolled coils, the energy consumption of steel joint enterprises is generally 23kJ/t per ton of steel, while the energy consumption of products produced by the short process of electric furnace steel mills using scrap steel as raw materials is close to 10kJ/t, which is about 60% lower.

3) With the annual output of scrap steel in the world exceeding 300 million tons, the development of short-process electric furnaces has played a good role in promoting environmental protection, digesting scrap steel, and purifying the environment of metallurgical plants. Therefore, developed countries have focused on developing compact short-process electric furnaces.

In recent years, although the development of electric furnace processes in my country has received attention, the development of short-process electric furnaces should be cautious, and can be developed appropriately, not blindly. Because under the current conditions, my country does not have advantages in electricity and scrap steel, that is, it does not have cost advantages. In Jiangyin Xingcheng Iron and Steel Co., Ltd., my country's first four-in-one short-process special steel production line has been built. The process flow is: 100t DC arc furnace smelting-LF, VD refining-R=12m large square billet continuous casting-hot delivery full continuous rolling. A full set of new equipment was introduced from Germany, which can develop and produce alloy structural steel, spring steel, gear steel, free-cutting steel, bearing steel, high-pressure boiler tube billet steel and other varieties. It will become a national enterprise with leading equipment level of high-quality steel and special steel and a capacity of over one million tons.

Due to the high thermal efficiency of large-capacity furnaces, the power consumption per ton of steel can be reduced. At the same time, the average equipment investment per ton of steel is also greatly reduced, the cost of steel is reduced, and labor productivity is improved. For example, the productivity of a furnace with a capacity of 320t is more than 100 times that of a small furnace with a capacity of 1.5t. In some special cases, when a large amount of high-quality molten steel is required, only a large-capacity electric arc furnace can meet the requirements. Therefore, many countries in the world use large-capacity electric arc furnaces. At present, there are more than 30 electric arc furnaces with a capacity of more than 180t, the largest of which is 400t. The electric arc furnace capacity of Baosteel in my country is the largest, at 150t.

Ultra-high power electric arc furnace refers to the energy input into the electric furnace per unit time is 2 to 3 times greater than that of ordinary electric arc furnaces. The main advantages are: greatly shortening the melting time and improving labor productivity; improving thermal efficiency and further reducing power consumption; using large current short arc, heat concentration, stable arc, and small impact on the power grid. The supporting equipment and related technologies include: using a large-capacity transformer to change the voltage under load; using a large area of ​​water-cooled furnace wall and water-cooled furnace cover on the furnace body; using oil-oxygen spray guns to assist melting of dead corner cold zones; using computer control, etc.

In 1979, Germany first changed the traditional 50t ultra-high power electric arc furnace to the center furnace bottom steel tapping, and then changed its electric furnace steelmaking to the more perfect eccentric furnace bottom steel tapping. The biggest feature of the eccentric furnace bottom steel tapping is that the steel tapping port is moved to the outside of the furnace shell, which is convenient for maintenance and overhaul. Eccentric furnace bottom steel tapping matches ultra-high power. In recent years, it has developed and promoted rapidly in developed countries, especially for large electric arc furnaces with slag-free operation. Its advantages are particularly obvious, mainly:
(1) More than 98% of slag can be retained in the molten pool;
(2) Refractory consumption can be reduced by about 25%;
(3) The temperature of molten steel generally only drops by about 25℃ during steel tapping;
(4) The steel tapping time is short, and the steel tapping time of a 60t electric arc furnace is only about 80s;
(5) The power consumption per ton of steel can be reduced by about 20kW·h;
(6) The electrode consumption per ton of steel can be reduced by about 0.5kg;
(7) The life of the refractory lining of the steel tapping port can reach about 250 times.

One of the biggest disadvantages of eccentric furnace bottom steel tapping is that the electric arc furnace must be an elevated structure. Most of the electric arc furnaces in my country are pit-type, with fewer elevated structures. In addition, the furnace capacity is small, the workshop equipment is aging, and it is difficult to transform. The development and promotion of eccentric furnace bottom steel tapping will still take a long time.

In 1982, the world's first DC arc furnace for actual production was manufactured in Germany. The central graphite electrode is connected to the circuit as the cathode, and the bottom electrode is the anode. It consists of two horizontal metals, with gas-conducting cooling fins installed on the metal plate, and many stylus pins attached to the metal plate, with magnesia sand filled between the stylus pins. The current is introduced into the stylus pins through the horizontal metal plate at the bottom of the furnace, and then into the molten pool. The operation of the DC arc furnace is not much different from that of the AC arc furnace, but in order to ensure good contact between the charge and the bottom electrode, a part of the molten steel must be retained when tapping. If the steel type is to be changed, the molten steel in the furnace must be drained out. For DC arc furnaces, new technologies such as eccentric bottom tapping, water-cooled furnace wall, water-cooled furnace cover, oxygen-burner, and scrap preheating are all suitable and have good effects. The main advantages of DC arc furnaces are: low electrode consumption, only about half of that of three-phase AC arc furnaces; low production costs. However, since it is still in the process of continuous improvement, there are also many problems: poor contact between the bottom electrode and the charge; oxidation and boiling of the steel rod bottom electrode; difficult maintenance of the steel pin (needle-shaped) bottom electrode; easy carbonization of graphite-magnesia bricks; uneven temperature in the furnace; poor heat dissipation of the bottom electrode, etc. Its disadvantage is that when the electricity price is high, the local cost is high.
my country's ultra-large DC electric arc furnace steelmaking production line was built and put into production in Shanghai Pudong Iron and Steel (Group) Company in September 1996. The production line consists of two l00t ultra-high power electric arc furnaces, two LF online ladle refining furnaces, a double-station vacuum smelting furnace and a 300mm×2000mm large slab continuous casting machine. It is matched with the company's 4200mm×3300mm double-frame wide and thick steel plate production line, forming a domestic and international first-class electric arc furnace production line for wide and thick plates, with an annual production capacity of 80×104t.