Views: 27 Author: Site Editor Publish Time: 2021-10-08 Origin: Site
Rapid melting and heating are the most important functions of electric arc furnace, which begins after the first basket of scrap is added to the furnace. In order to melt the scrap steel and make the molten steel temperature reach the tapping temperature in the shortest possible time, the following operations are generally carried out in the EBT electric furnace: power supply at the maximum possible power, oxygen one burner nozzle melting, oxygen blowing and stirring, bottom blowing mixing, foam slag and other intensified smelting and heating technologies.
Dephosphorization in electric arc furnace is mainly carried out by controlling slag oxidizability, lime content and temperature. The main processes adopted include:
a. Strengthen oxygen blowing and oxygen combustion to improve the oxidizability of primary slag.
b. Foamed slag with high oxidizing and basicity in advance. And make full use of the favorable conditions of low melting temperature to improve the ability of dephosphorization of slag.
c. Release the initial slag with high phosphorus content in time and supplement new slag to prevent slag phosphorus from returning after temperature rise and during tapping.
d. Adopt injection operation to strengthen dephosphorization. Lime and fluorite powder are directly blown into the molten pool with oxygen. The dephosphorization rate is generally up to 80%, and desulfurization can be carried out at the same time. The desulfurization rate is close to 50%.
e. Adopt slag free tapping technology to strictly control the amount of slag and minimize the phosphorus after tapping. Generally, the amount of slag can be controlled at 2 kg/t. For the slag with (P2O5) = 1%, the phosphorus return amount is ≤ 0.001%.
The control of tapping phosphorus content shall be comprehensively considered according to product specification, alloying and other conditions, generally less than 0.02%.
High carbon content is adopted for electric furnace proportioning. The main purposes are:
a. When oxygen is blown and melted during melting period, carbon oxidizes before iron, which can reduce the burning loss of iron.
b. Carburizing can reduce the melting point of scrap steel and accelerate the melting;
c. The carbon oxygen reaction causes the stirring of the molten pool and promotes the slag steel reaction, which is conducive to early dephosphorization.
d. During the refining heating period, the active carbon oxygen reaction expands the slag steel interface, which is conducive to further dephosphorization, homogenization of liquid steel composition and temperature and floating of gas and inclusions.
e. Active carbon and oxygen reaction can help the formation of foam slag, increase the heat transfer efficiency and accelerate the heating process.
EBT electric furnace alloying is generally completed in the ladle during tapping. Those alloys that are not easy to oxidize and have high melting point can be added to the furnace after melting, such as Ni, W, Mo and other ferroalloys. However, when steel retention operation is adopted, the influence of steel retention in the front furnace on the composition of molten steel in the next furnace shall be fully considered. During tapping, the tapping temperature should be properly adjusted according to the amount of alloy added. In addition, good ladle baking and heat compensation in the ladle can improve the alloy yield without causing low temperature.
During tapping, alloying in the ladle is pre alloying, and accurate alloy composition adjustment is finally completed in the refining furnace. To adjust the composition smoothly in the refining process, pre alloying is required so that the adjusted composition doesn’t exceed the middle limit of the specification.
Good temperature control is the guarantee for the successful completion of the metallurgical process. For example, dephosphorization requires not only slag with high oxidation and high alkalinity, but also good temperature coordination, which is the reason why it’s emphasized that dephosphorization should be carried out in the early stage. The lower temperature at that time is conducive to dephosphorization. In the oxidation refining period, in order to cause active carbon and oxygen boiling, a higher temperature (> 1550 ℃) is required. To make the post-treatment and pouring of the furnace proceed normally, the initial molten steel of the electric furnace is required to have a certain degree of overheating according to the different processes adopted, so as to compensate the temperature loss in the tapping process, refining outside the furnace and liquid steel transportation.