Why must the new electric arc furnace for steelmaking be dried up - part 2

New furnace body usually needs to be dried

Low voltage and small current must be used to slowly heat up the brine furnace (carbon free furnace lining). If the temperature rises rapidly, the brine will vaporize violently and cause furnace bottom cracking and furnace wall cracking.

In the process of furnace drying, it is necessary to arrange an interval to cut off power, check the electrode position of furnace drying, furnace lining sintering, equipment and water cooling system, and it is also conducive to the uniform permeability and air outlet of furnace bottom and furnace wall temperature. At present, many EAF steel plants also adopt the method of direct steelmaking without oven drying. According to the requirements of the varieties smelted by the electric arc furnace and the use of water-cooled furnace wall, the traditional furnace drying method and the direct steelmaking method without furnace drying can be adopted for the newly built electric arc furnace. However, if the method of direct steelmaking without furnace drying is adopted, corresponding measures should be taken to complete the task of furnace drying according to the characteristics of the new furnace. Because DC electric arc furnace has bottom electrode and mostly uses water-cooled furnace wall, it generally does not specially dry the furnace, but uses the technology of direct steelmaking and baking without drying the furnace. Its requirements are similar to that of AC arc furnace, while the arc operation is the same as that of conventional DC arc furnace. The direct steelmaking method without oven drying is a method of directly charging and steelmaking without pre baking a new furnace before using a new asphalt magnesia furnace lining, and using the high temperature during smelting to achieve the purpose of sintering the furnace lining. Without pre heating, it can save electricity, coke, time and increase steel output. It has been widely used.

When directly steelmaking without oven drying, water is brought into the furnace during bricklaying, which is decomposed into hydrogen and oxygen at high temperature and dissolved in the molten steel, which is easy to cause the steel ingot to swell or subcutaneous bubbles. Therefore, the direct steelmaking method without oven drying requires that the melting period should be slow to facilitate furnace bottom sintering. During the oxidation period, the amount of decarburization should be appropriately increased. Batch ore feeding and oxygen blowing are combined for oxidation to make a large amount of gas dissolved in the steel fully escape.) the reduction period should not be too long to reduce the further absorption of the steel from the atmosphere.

The first furnace should be smelted with 35 ~ 60 steel, preferably 35 steel. During furnace laying, dry magnesia and solid asphalt powder shall be used as filler for dry laying. Clean, dry, medium and small size high-quality scrap shall be used for batching, and the carbon content shall be more than 0.2% higher than the conventional one, so as to ensure that the decarburization amount in the oxygen blooming period is not less than 0.4%. Before charging, the furnace bottom should be properly added with more lime and paved (the DC electric arc furnace has a furnace bottom electrode, so it is not allowed to add lime at the furnace bottom, which can be added gradually after the formation of the molten pool). After the electrode passes through the well to the bottom, the current shall be reduced appropriately to avoid the furnace bottom turning over due to excessive heating. It is not appropriate to blow oxygen to aid melting too early in the melting period (80% - 90% of the furnace charge is melted or even no oxygen is blown). After the furnace charge is melted, it can stay for a period of time (20 ~ 30min) to facilitate the escape of furnace lining gas, and it is better to change the slag. During the oxidation period, it is necessary to strengthen the degassing by boiling, ensure good uniform boiling, but avoid large boiling. A small amount of ore should be added in multiple batches (the ore amount should not be less than 3% ~ 5% of the material weight). The oxygen pressure should not be too large during oxygen blowing, and the insertion depth should not be too deep. Before all slag pulling, the round cup sample (inserted with aluminum or added with ferrosilicon powder for deoxidization) shall shrink well without swelling, otherwise it shall be degassed again. The reduction period shall be shortened as far as possible to reduce liquid steel suction. It is best to use the return slag method or the quick white slag method. The tapping temperature shall be controlled at the middle and lower limits to prevent high-temperature and low-temperature tapping. The steel port of the first furnace is not blocked, and it should be connected frequently at the later stage of oxidation to allow the flame to blow out and sinter this part of the furnace lining. The tapping trough shall be baked with firewood or gas at the beginning of power on.