Importance of Graphite Electrode in Electric Arc Furnace Steelmaking

Application of Graphite Electrode in Electric Arc Furnace Steelmaking

As a whole, EAF steelmaking can be divided into five stages: raw material collection, preparation before smelting, melting period, oxidation period and reduction period.

1. Collection of Raw Materials

Scrap steel is the main material for electric arc furnace steelmaking. The quality of scrap steel directly affects the quality, cost, and productivity of graphite electrodes. Therefore, there are the following requirements for scrap steel:

(1) The surface of scrap steel should be clean and less rusty, because the sediment and other sundries in the scrap steel will reduce the conductivity of the charge, prolong the melting time, affecting the dephosphorization effect in the oxidation period and erode the furnace lining. When the scrap steel is seriously rusted or stained with oil, it will reduce the yield of steel and alloy elements and increase the hydrogen content in the steel.

(2) Scrap steel shall not be mixed with lead, tin, arsenic, zinc, copper, and other non-ferrous metals. Lead has a high density, low melting point and is insoluble in liquid steel. It is easy to deposit in the gap at the bottom of the furnace, resulting in steel leakage. Tin, arsenic and copper are easy to cause hot embrittlement of steel.

(3) The scrap shall not be mixed with sealed containers, inflammable, explosives and poisons to ensure safe production.

(4) The chemical composition of scrap steel should be clear, and the content of sulfur and phosphorus should not be too high.

(5) The overall dimension of scrap steel shall not be too large (the cross-sectional area shall not exceed 150mm) × 150mm, the larger length should not exceed 350mm). In EAF steelmaking, pig iron is generally used to increase the carbon content of the charge, which usually does not exceed 30% of the charge.

2. Preparation before Smelting

Batching is an indispensable part of the graphite electrode steelmaking process. Whether the batching is reasonable or not is related to whether the steelmaker can carry out the smelting operation normally according to the process requirements. Reasonable proportioning can shorten the smelting time.

When batching, attention should be paid to: first, the batching calculation must be carried out correctly and the charge loading must be weighed accurately. Second, the size of the charge should be matched according to the proportion, so as to achieve the purpose of good loading and fast transformation. Third, all kinds of furnace charges should be used in combination according to the quality requirements of steel and smelting methods. Fourth, the ingredients must meet the process requirements.

3. Melting Period

In the electric arc furnace steelmaking process, the melting period is called from the beginning of power onto the full melting of the furnace charge. The melting period accounts for about half of the whole smelting time, and the power consumption accounts for about 2 / 3 of the total power consumption.

The task of the melting period is to quickly melt and heat up the furnace charge with the least power consumption on the premise of ensuring the service life of the furnace body, and making the slag in the burning period, so as to stabilize the arc and prevent suction and early dephosphorization.

(1) Arcing stage. When energizing and starting the arc, the furnace is full of charge, and the arc is close to the furnace top. If the input power is too large and the voltage is too high, the furnace top is easy to be burned out. Therefore, about 2 / 3 of the rated power of the input transformer and the intermediate voltage are generally selected.

(2) Drilling stage. At this stage, the arc is completely surrounded by the charge, and almost all the heat is absorbed by the charge, which will not burn the furnace lining. Therefore, higher power is used. Generally, the drilling time is about 20min, accounting for about 1 / 4 of the total melting time.

(3) Graphite electrode rising stage. After the graphite electrode "passes through the well" to the end, a molten pool has been formed at the bottom of the furnace, and the lime and some elements at the bottom of the furnace are oxidized to form a layer of slag on the steel liquid level. The surrounding furnace charge continues to melt by radiant heat. The increase of liquid steel increases the liquid level, and the graphite electrode gradually rises. At this stage, higher power is still used to transmit electric energy, accounting for about 1 / 2 of the total melting time.

(4) The last class melts. After more than 3 / 4 of the charge is melted, the arc can no longer be shielded by the charge, and the high-temperature area under the three graphite electrodes has been connected into one. At this time, if a higher power is used for a long time, the arc will strongly damage the furnace cover and furnace wall.

The main task of the melting period is to melt the charge, but in the melting period, it is not only to make slag, but also an important operation content of the melting period. If only to meet the requirements of covering liquid steel and stabilizing arc, only 1% ~ 1.5% of the slag amount is enough. However, considering the requirements of dephosphorization, the molten slag must have a certain oxidizability, alkalinity, and slag amount.

Inquire freely at [email protected] or [email protected].

Kindly click on the article you are interested in:

What is Metallurgical Equipment?

What Is the Ladle Refining Furnace?

Alkaline EAF Oxidation Smelting Process

Where Is Induction Furnace Used?

Leakage Detection of the Induction Furnace

Comparison of Electric Furnace, AOD furnace, LF furnace and VD Vacuum Furnace

Energy Saving and Emission Reduction in Steelmaking Production

Energy-Saving Technology for Heat Treatment of Induction Furnace

Walking Beam Reheating Furnace VS Push-steel Reheating Furnace

Cause Analysis and Solution of Induction Coil Blocking in Medium Frequency Smelting Furnace