How to Reduce Oxygen Content in Ladle Refining Furnace Steel: Key Control Measures

In steelmaking, controlling oxygen content is essential for improving steel cleanliness, reducing non-metallic inclusions, and achieving stable casting performance. For steel producers using a Ladle Refining Furnace (LRF), oxygen control depends not only on deoxidizer additions, but also on slag design, argon stirring, refractory selection, and aluminum control.

As an electric arc furnace (EAF) equipment manufacturer, Sanrui Electric Furnace focuses on practical process and equipment solutions for secondary steel refining. Based on industrial refining principles, the following measures can help steelmakers achieve more effective oxygen control during LRF treatment.

1. Select the Right Refining Slag System

Refining slag performs several functions during ladle refining, including deoxidation, desulfurization, inclusion absorption, and arc shielding. Proper slag composition is therefore critical to reducing dissolved oxygen and improving steel cleanliness.

Increasing slag basicity generally helps lower the equilibrium oxygen content in molten steel while improving the sulfur distribution ratio between slag and steel. However, excessively high basicity is not necessarily beneficial.

When slag basicity becomes too high, such as above approximately 5.0, the slag melting temperature may increase and slag formation can become slower. This can negatively affect deoxidation, desulfurization, and inclusion absorption.

For many LRF refining applications, a slag basicity of approximately 2.5–3.0 can provide a practical balance between:

• Deoxidation performance

• Desulfurization efficiency

• Non-metallic inclusion absorption

• Slag fluidity

• Arc coverage and heat preservation

  
  

The actual slag system should still be optimized according to steel grade, raw materials, temperature, sulfur target, and production conditions.

2. Optimize Argon Stirring During Ladle Refining

Argon stirring is one of the most important process controls for improving molten steel cleanliness. It contributes to oxygen reduction in two main ways: promoting the removal of dissolved gases and enhancing the flotation of non-metallic inclusions.

2.1 Removal of Dissolved Oxygen

During LRF treatment, argon can be injected through porous plugs at the bottom of the ladle. As argon bubbles rise through the molten steel, they create local low-partial-pressure regions and promote mass transfer between the steel and gas phase.

The resulting bath circulation improves contact between molten steel, slag, and argon bubbles, helping remove dissolved gases and promoting refining reactions.

Effective argon stirring should therefore be designed to provide sufficient bath mixing without causing excessive turbulence.

2.2 Removal of Non-Metallic Inclusions

Argon bubbling also promotes the flotation and removal of non-metallic inclusions such as Al₂O₃ and SiO₂.

The inclusion-removal process generally involves:

1. Collision between inclusions and argon bubbles.

2. Attachment of inclusions to bubble surfaces.

3. Bubble flotation through the molten steel.

4. Transfer of inclusions into the refining slag.

   
   

The probability of inclusion removal depends on factors such as inclusion size, bubble size, bubble population, steel cleanliness, and interfacial properties.

Larger inclusions generally have a higher probability of colliding with rising bubbles than very small inclusions. At the same time, generating a sufficient number of appropriately sized bubbles can improve inclusion flotation.

2.3 Use Soft Argon Blowing for Inclusion Removal

Argon flow rate has a direct influence on bubble formation and bath turbulence. Excessively strong argon stirring can generate larger bubbles and cause violent movement of the steel and slag.

For inclusion removal, soft argon stirring combined with sufficient treatment time is generally more favorable.

Practical measures include:

• Using relatively low-intensity argon stirring during the clean-steel stage.

• Extending the soft-blowing period when production conditions permit.

• Using multiple porous plugs where appropriate to improve bath circulation.

• Avoiding excessive turbulence at the steel-slag interface.

• Maintaining stable slag coverage during argon treatment.

  
  

The objective is to achieve effective steel circulation and inclusion flotation while minimizing slag entrainment and secondary oxidation.

2.4 Maintain an Inert Protective Atmosphere

Argon also provides protection against secondary oxidation.

During LRF refining, argon escaping from the molten steel can help form an inert atmosphere above the bath. This reduces direct contact between molten steel and atmospheric oxygen.

Maintaining adequate argon protection throughout the refining process can therefore help prevent reoxidation, which is particularly important after deoxidation and during the final stages of ladle treatment.

3. Select Suitable Refractory Materials

Refractory materials can also influence steel oxygen levels. During LRF operation, refractory wear and chemical interaction with molten steel and slag may introduce oxides or inclusions into the steel.

LRF operation involves:

• Rapid temperature changes

• High-temperature exposure

• Continuous argon stirring

• Slag-metal interaction

• Mechanical and thermal erosion

  
  

Therefore, ladle and refining-furnace refractories should have good thermal shock resistance, high-temperature strength, corrosion resistance, and wear resistance.

Suitable refractory selection helps reduce refractory erosion and minimize the risk of refractory-derived inclusions entering the molten steel.

For an LRF system, refractory design should be considered together with slag chemistry, argon stirring intensity, operating temperature, and steel grade rather than treated as an isolated factor.

4. Control Acid-Soluble Aluminum (Als)

Aluminum is widely used as a deoxidizer in steelmaking, but excessive residual aluminum can negatively affect steel cleanliness.

For aluminum-killed steel, controlling acid-soluble aluminum (Als) within the required range is important for maintaining stable deoxidation while limiting excessive Al₂O₃ formation.

When aluminum additions are excessive, aluminum can react with oxygen-containing components in the slag, including SiO₂ and MnO, and promote the formation or accumulation of Al₂O₃ inclusions in the molten steel.

Excessive residual aluminum may also increase the risk of reoxidation-related inclusion problems during casting if process conditions are not properly controlled.

A practical target for some steel grades is approximately 0.015–0.030% Als, although the optimum range should be determined according to the specific steel grade, product requirements, deoxidation practice, and casting process.

The key is not simply to maximize aluminum content, but to maintain sufficient aluminum for effective deoxidation while avoiding unnecessary excess.

5. Coordinate Slag, Argon, Refractory and Deoxidation Control

Reducing oxygen content in an LRF is a systematic process rather than a single-operation adjustment.

A stable refining process should coordinate the following four factors:

Temperature control, slag-metal reactions, argon flow, treatment time, and protection from atmospheric oxygen should also be considered together.

6. LRF Equipment Design Matters for Steel Cleanliness

Although oxygen control is fundamentally a metallurgical process, LRF equipment design and operating stability directly affect refining performance.

A well-designed ladle refining furnace should provide stable electrical heating, reliable electrode operation, effective argon stirring, controlled slag coverage, and consistent process conditions.

At Sanrui Electric Furnace, LRF and EAF solutions are developed for industrial steelmaking applications, with equipment configurations designed around the customer's production capacity, steel grades, refining requirements, and plant conditions.

For steel producers seeking lower oxygen levels and improved steel cleanliness, equipment selection should therefore be evaluated together with the complete refining process rather than focusing on individual components alone.

Conclusion

Reducing oxygen content during ladle refining requires coordinated control of refining slag, argon stirring, refractory materials, aluminum content, and secondary oxidation.

A suitable slag basicity of around 2.5–3.0, controlled soft argon stirring, high-performance refractories, stable inert-gas protection, and appropriate Als control can provide a practical foundation for improving steel cleanliness.

For different steel grades and production targets, however, the optimum parameters may vary. LRF equipment configuration and metallurgical process design should be matched to the actual production conditions to achieve stable and repeatable refining results.

Sanrui Electric Furnace provides EAF and LRF equipment solutions for steelmaking plants, supporting customers with equipment configurations tailored to production capacity, refining requirements, and process conditions.

Frequently Asked Questions

1. Why is oxygen control important in LRF refining?

Lower oxygen content helps reduce non-metallic inclusions, improve steel cleanliness, and enhance the quality and consistency of finished steel products.

2. How does refining slag reduce oxygen content?

A properly designed refining slag promotes deoxidation reactions, absorbs non-metallic inclusions, and helps prevent reoxidation of the molten steel.

3. Does stronger argon stirring always improve oxygen removal?

No. Excessively strong stirring can increase turbulence and slag entrainment. Controlled or soft argon stirring is generally more suitable during the final inclusion-removal stage.

4. What is a suitable slag basicity for LRF refining?

A basicity of approximately 2.5–3.0 can provide a practical balance between deoxidation, desulfurization, inclusion absorption, and slag fluidity for many applications. The optimum value depends on the steel grade and process conditions.

5. Why is refractory selection important for oxygen control?

Refractory erosion can introduce oxides and inclusions into molten steel. Good thermal shock resistance, high-temperature strength, and corrosion resistance can help minimize this risk.

6. What is the role of acid-soluble aluminum in oxygen control?

Als provides an indication of the aluminum remaining in aluminum-killed steel. Proper control helps maintain effective deoxidation while limiting excessive Al₂O₃ inclusion formation.

7. Can LRF equipment affect steel cleanliness?

Yes. Stable heating, effective argon stirring, reliable slag coverage, and consistent refining conditions all contribute to stable secondary metallurgy and steel cleanliness.