Analysis and treatment methods for various abnormal situations in the melting period of EAF steelmaking

By reading this article, Analysis and treatment methods for various abnormal situations in the melting period of EAF steelmaking as following:

(1) Reasons and treatment methods for non-conductivity during the melting period
(2) Phenomenon and treatment method of “shacking” material collapse of furnace charge
(3) Causes of sticking cold steel at the furnace bottom at the end of melting and inspection and treatment methods
(4) Oxygen blowing to aid melting and slumping will cause large boiling phenomenon and preventive treatment methods

In the process of electric arc furnace steelmaking, the melting period is called the melting period from the beginning of electrification to the complete melting of the charge. The melting period accounts for about half of the entire smelting time, and the power consumption accounts for about 2/3 of the power consumption of the whole furnace. During the melting period, due to many reasons such as operation or the furnace itself, furnace lining, etc., various abnormal situations may occur. The 4 abnormal situations are listed below, and the reasons for their occurrence and the treatment methods are clearly introduced.

EAF Furnace Construction Worker
EAF Furnace Construction

(1) Reasons and treatment methods for non-conductivity during the melting period

The non-conduction of power transmission during the melting period is mainly due to the excessive resistance between the electrode and the charge, which hinders the current loop. The reason is as follows.

① Sometimes the furnace charge is mixed with non-conductive refractory materials, steel slag, etc. It is easy to cause a phase current interruption.

②The gap between the furnace charge is too large and the contact with each other is poor, which will cause the current interruption of the three electrodes. Due to the mechanical failure of the electrode lifting frame or the electrodes are stuck by the water cooling ring, the electrodes cannot be lowered and the non-conduction phenomenon occurs.

When a non-conductive phenomenon is found, find out the reason and deal with it. If the charge is poorly conductive, some coke blocks or small electrode blocks can be added under the poorly conductive electrodes to help start the arc. If there are no coke blocks and electrode fragments, some clean small scrap steel and pig iron blocks can also be added. When conditions permit, it is better to hydraulically inject the remaining steel of the same steel type under the non-conductive electrode. Among these measures, the small electrode has the longest action time and the best effect. Because it conducts electricity well and is not easy to burn quickly, but the electrode block should not be too large, otherwise it will not be burned after the conduction is completed, which will increase the carbon content of molten steel and prolong the smelting time. If the electrode cannot be lowered due to mechanical failure of the electrode lifting frame or the electrode is stuck by the water cooling ring, it should be repaired.

(2) Phenomenon and treatment method of “shacking” material collapse of furnace charge

Improper oxygen blowing and boosting results in high boiling, and the steel slag splashes on the steel material, making the unmelted iron material and steel slag stick together, resulting in a serious “shacking” phenomenon. Furnace materials with “shacking” phenomenon are mostly of poor quality, low carbon content of scrap steel, and the furnace materials are sticky and difficult to melt during oxygen blowing and boosting, which greatly prolongs the time of oxygen blowing and boosting. If the furnace charge is not well loaded, especially if the lower charge is not packed tightly, when the lower charge melts, the upper charge will not be supported, and the phenomenon of slump will occur. In order to ensure that the material does not collapse during the melting period, it is necessary to have a suitable distribution method. During oxygen blowing and boosting, it is found that “building a shed” should adopt the method of cutting and pushing materials while blowing oxygen, instead of blowing one furnace charge in a centralized manner. If there is a “shacking” phenomenon, it should be cut with oxygen immediately to make the charge fall into the molten pool. If the carbon content of the charge is low, you can add crushed electrode blocks to the molten pool, and blow oxygen while increasing the carbon, which can not only ensure the carbon content of the molten steel, but also speed up the melting of the charge and shorten the smelting time.

EAF Bottom Ramming Mass
EAF Bottom Ramming Mass

(3) Causes of sticking cold steel at the furnace bottom at the end of melting and inspection and treatment methods

①Several reasons for furnace bottom sticking

a. The steel itself is relatively refractory, and it is easy to cause sticking to the bottom of the furnace, such as large pieces of low-carbon steel, tungsten iron, etc.

B. When electrification “piercing the well” the electrode is not at the bottom or after the electrode is at the bottom, the time is not long, and it rises quickly, so that the refractory material at the bottom of the furnace cannot be fully heated, which will cause the bottom of the furnace to be refractory. For example, if a very high voltage is used for power transmission after energization and “well penetration” during melting, due to the high voltage and high arc power, the “well” through which the charge is penetrated is large and melts quickly, and the molten steel level at the furnace bottom Therefore, the arc of the electrode stays in the bottom part of the furnace for a relatively short time. Although the upper material melts quickly and the molten steel level rises rapidly, the material buried in the bottom of the furnace is not fully heated by the arc, so it melts. Extremely slow, resulting in a sticky furnace bottom.

c. Large pieces of slag steel in the furnace charge are often not easily melted due to poor heat transfer of the slag, and stick to the bottom of the furnace.

②Inspection and treatment method Before oxidation starts, use a long-rod iron rake or iron hook to touch the surrounding furnace slope and furnace bottom to check whether there is scrap steel. Observe the molten pool in the furnace, if there is a local tumbling phenomenon, it means that there is cold steel. The temperature of molten steel is obviously not easy to rise, which means that there is the possibility of cold steel. When the charge or large piece of steel is refractory, deep blowing oxygen can be used to increase the temperature of the molten steel at the bottom of the furnace and accelerate the melting of the charge. When there is a large piece of steel scrap at the bottom of the furnace, do not let the electrode rise too fast, and use deep oxygen blowing to help the melting.

(4) Oxygen blowing to aid melting and slumping will cause large boiling phenomenon and preventive treatment methods

When the molten steel is poured on the iron plate during the melting period, a large number of sparks can be seen. This is because when the temperature of the molten steel is lowered, the balance of carbon and oxygen in the molten steel is out of balance, and oxygen will react with carbon to produce CO gas. When slumping during the melting period, due to the sudden decrease in the temperature of the molten steel, the carbon-oxygen reaction is prompted to occur sharply. In addition, there are rust spots on the surface of scrap steel, etc., which provide good conditions for the generation of air bubbles. In addition, due to the generally low temperature in the melting period and the poor reaction conditions of slag steel, it is easy to accumulate excessive iron oxide in the slag. When the slump boils, the contact between slag and steel is promoted, and the accumulated iron oxide and carbon act, which also promotes the melting process. Big boil phenomenon. Slumping occurs in the early stage of melting, and the boiling is weak. This is because the content of iron oxide in the slag in the early stage of melting is not large, the temperature of molten steel is low, and the temperature difference is small. When slumping occurs during oxygen blowing and fluxing, the reaction is more violent. If the oxygen blowing time is longer or the slump occurs after adding iron ore, at this time, because more iron oxide is accumulated in the slag and the temperature of molten steel in the furnace reaches the temperature condition of carbon-oxygen reaction, the boiling will be more intense. Once the large boiling phenomenon of material collapse occurs, the mild case will cause a steel running accident, and the severe case will cause the furnace cover to collapse and personal accidents.

In order to avoid the sudden collapse of oxygen blowing and fluxing, it is necessary to master the correct oxygen blowing method. During the oxygen blowing process, observe the distribution of the furnace to achieve a purposeful oxygen blowing operation; do not stay in one place for concentrated oxygen blowing, and constantly move the position of the oxygen tube to prevent local voids and “bridges”.

When boiling occurs, the emergency measure to be taken is to lift the electrode to raise the furnace cover after power failure, to reduce the gas pressure in the furnace, and the furnace must not be tilted. At the same time, add a small amount of ferrosilicon powder to the molten pool for deoxidation, prevent the carbon-oxygen reaction from continuing, and eliminate the phenomenon of large boiling. If the boiling is violent, the operator should immediately evacuate the stove and evacuate to a safe place to avoid personal accidents.

EAF Refractory Products
EAF Refractory Products

This article describes in detail the analysis and treatment methods for various abnormal situations in the melting period of EAF steelmaking. If you are interested in ladles, tundishes and other furnaces, welcome to contact us, we will provide you with excellent solutions and industry information.

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