In Electric Arc Furnace (EAF) steelmaking, the oxidation period plays a critical role in decarburization, dephosphorization, and the improvement of molten steel cleanliness.
In a previous article, different oxidation methods used during the EAF oxidation period—namely oxidation by adding oxidizing agents, oxygen blowing, and the combined oxidation method—were systematically introduced.
This article focuses on the practical operational precautions associated with these oxidation methods in order to avoid abnormal furnace conditions and ensure stable steelmaking quality.
Why Should Excessive Oxidizing Agents Not Be Added Before Charging in an EAF?
Decarburization reactions in an electric arc furnace require an adequate molten steel temperature. Adding excessive oxidizing agents before charging introduces a strong endothermic effect, which increases electrical energy consumption and lowers the bath temperature.
More importantly, iron oxides tend to accumulate at the steel–slag interface. Once the temperature becomes suitable, intense carbon–oxygen reactions may occur, potentially leading to violent bath boiling.
Therefore, large amounts of oxidizing agents should not be added before charging. Only a small quantity may be used, which is beneficial for early slag formation and preliminary dephosphorization.
Why Is a Minimum Temperature Required Before Starting Ore Oxidation?
Carbon–oxygen reactions in molten steel can only proceed intensively above a certain temperature. For molten steel with a carbon content of approximately 1%, significant carbon oxidation begins at around 1550°C.
If ore is added too early at insufficient temperature, decarburization efficiency remains low while iron oxides may accumulate at the interface. As the temperature later increases, this condition can easily trigger sudden and severe boiling.
For this reason, a minimum temperature for ore oxidation is specified in EAF steelmaking practice to ensure stable reactions and to reduce operational risks.
Why Is the “Ore First, Oxygen Later” Sequence Recommended in Combined Oxidation?
When applying the combined oxidation method during the EAF oxidation period, the operating sequence of adding ore first and then blowing oxygen is generally recommended.
Adding ore first promotes relatively uniform and widespread bath boiling, which is favorable for the removal of dissolved gases and non-metallic inclusions. At the same time, ore oxidation absorbs a large amount of heat, helping to lower the bath temperature and create more favorable conditions for dephosphorization.
If oxygen blowing is applied first, the molten steel temperature tends to rise rapidly, which is unfavorable for phosphorus removal and reduces the overall metallurgical effectiveness of the oxidation period.
How Should Lance Immersion Depth and Angle Be Controlled During Oxygen Blowing?
During oxygen blowing in EAF steelmaking, lance operation has a direct impact on furnace safety and metallurgical performance.
- Excessive immersion depth may cause the oxygen jet to strike the furnace bottom or sidewall, resulting in severe refractory damage. It also increases metal splashing, gas absorption, and cooling losses, slows temperature rise, and promotes slag–metal adhesion on the furnace roof. This increases the risk of water-cooled panel failure and accelerates lance consumption.
- Insufficient immersion depth limits oxygen interaction mainly to the slag surface, leading to poor decarburization efficiency and low oxygen utilization. However, shallow blowing can accelerate bath temperature increase and is sometimes beneficial when the steel temperature is too low.
In practice, the oxygen lance is typically positioned approximately 5–10 cm near the steel–slag interface.
The lance angle is equally important. An excessively steep angle effectively causes over-deep blowing, while too shallow an angle results in slag-surface oxidation only. A lance angle of around 30° is commonly adopted in industrial EAF operations.
How Should Oxygen Pressure Be Properly Controlled During Oxygen Blowing?
Oxygen pressure significantly influences melting efficiency, bath reactions, and steel quality during the EAF oxidation period.
- Excessively high oxygen pressure can accelerate scrap melting and decarburization, but it also causes severe oxide splashing, increases cold steel adhesion on furnace walls and roof, and reduces oxygen utilization. During decarburization, overly violent boiling may promote gas absorption by the molten steel, deteriorating steel quality and worsening furnace front operating conditions.
- Excessively low oxygen pressure results in slow melting and decarburization, prolongs heat time, and produces weak bath boiling, which is unfavorable for gas and inclusion removal.
Therefore, oxygen pressure must be carefully selected and consistently controlled according to furnace conditions.
Why Is Oxygen Blowing Prohibited at Too Low Oxygen Pressure?
When oxygen pressure is too low, most of the oxygen reacts with iron at the steel–slag interface, forming iron oxides that accumulate in the slag. Meanwhile, insufficient bath stirring limits carbon mass transfer toward the reaction interface.
Under these conditions, once the temperature rises, the bath becomes highly susceptible to sudden and violent boiling. For this reason, oxygen blowing should not be carried out when oxygen pressure is insufficient during EAF steelmaking.
