In modern steel production, off-furnace refining has become the core link to ensure the quality of molten steel and improve product performance. Especially in electric furnace steelmaking, molten steel often contains high levels of gas and inclusions, which must be further purified through off-furnace refining to meet the increasingly stringent clean steel standards.
The main purpose of off-furnace refining
The core goal of off-furnace refining is to:
- Remove harmful elements: such as phosphorus, sulfur, nitrogen, hydrogen, oxygen and other five major impurity elements, which have a great impact on the performance of steel. Modern technology can control the total impurity content in steel below 0.005%.
- Precise control of composition and temperature: to achieve precise adjustment of steel composition and strictly control the temperature of molten steel to meet the needs of stable continuous casting operation.
- Improve the morphology of inclusions: through modification treatment, such as spheroidizing sulfides and converting alumina into calcium aluminate, the machinability and performance stability of steel are improved.
Five major tasks of off-furnace refining
- Enhance refining efficiency: share part of the refining task of the primary refining furnace, complete key metallurgical reactions under better thermodynamic and kinetic conditions, and improve overall production efficiency.
- Homogenization of composition: with the help of stirring means, the composition and temperature of the molten steel are uniform to avoid local segregation.
- Accurate temperature control: achieve constant molten steel temperature, ensure the stability of the continuous casting process, and reduce the impact of the temperature difference of the tundish on the quality of the ingot.
- Purification of molten steel: further remove gas and inclusions, control their morphology, and minimize their impact on steel performance.
- Connecting processes and improving flexibility: The off-furnace refining device plays a buffering role between the electric furnace and continuous casting, improving the overall flexibility and rhythm adjustment capabilities of the system.
Key functions of off-furnace refining equipment
To complete the above tasks, modern off-furnace refining systems usually have the following functional modules:
- Molten steel stirring: to make the temperature and composition uniform, and at the same time facilitate the floating of inclusions and the reaction of steel slag;
- Heating and temperature control system: such as arc heating, to ensure that the molten steel reaches the ideal temperature;
- Refining treatment: including degassing, desulfurization, decarburization, removal of inclusions and inclusion denaturation, etc.;
- Alloy adjustment: to accurately achieve narrow range control of alloy elements;
- Production rhythm adjustment: to reconcile the rhythm difference between electric furnace steelmaking and continuous casting machine.
Main categories of off-furnace refining
The off-furnace refining process is divided into two categories: vacuum and non-vacuum. According to the needs, heating, stirring (such as argon blowing, stirring electrode), wire feeding (desulfurization, calcium feeding), powder spraying, oxygen blowing and other means can be flexibly combined to improve the refining effect, compensate for heat loss and achieve composition adjustment.
For example, the LOD furnace is one of the non-vacuum off-furnace refining furnace. It is independently developed by our company, Shanghai Metallurgy Equipment Group, is a typical off-furnace refining furnace. It has three major metallurgical functions: decarburization, dephosphorization and bottom blowing argon stirring. The ‘induction furnace + LOD furnace + ladle refining furnace’ steelmaking process is easy-to-implement with low investment, making it suitable for small to medium sized steelmaking project.
