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BOF Slag Splashing Technology: Principle, Process Control, Advantages and Limitations

Sep. 25, 2026

BOF Slag Splashing Technology: Principle, Process Control, Advantages and Limitations

In Basic Oxygen Furnace (BOF) steelmaking, the refractory lining is continuously exposed to molten steel, high-temperature slag, oxidizing atmospheres, and mechanical erosion. The rate of refractory wear directly affects converter campaign life, refractory consumption, production efficiency, maintenance requirements, and overall steelmaking cost.

Slag splashing, also known as slag splashing furnace protection, is a widely used BOF refractory maintenance technology. By controlling the composition of the end-point slag and using high-flow inert gas to splash the slag onto the refractory working surface, a protective slag coating can be formed on the furnace lining.

This protective layer reduces direct contact between the refractory lining and aggressive slag or molten steel, helping extend converter campaign life and reduce refractory consumption.

As a professional metallurgical equipment manufacturer, Sanrui Electric Furnace focuses on the development and manufacturing of electric arc furnaces, refining furnaces, and related steelmaking equipment. For modern steel plants, proper furnace design, bottom stirring systems, gas control, refractory selection, and process optimization are important for achieving stable and long-life operation.

1. What Is BOF Slag Splashing?

BOF slag splashing is a refractory protection process performed after tapping.

A controlled amount of hot end-point slag is retained in the converter. The slag composition is adjusted according to the refractory material and process requirements. High-flow nitrogen or another suitable process gas is then injected through the bottom stirring system.

The gas rapidly agitates the retained slag and causes it to splash onto the refractory working surface.

When the hot slag contacts the refractory lining, it cools, solidifies, and bonds with the working surface, forming a relatively stable protective slag coating.

This protective coating acts as a buffer between the refractory lining and the high-temperature steelmaking environment.

The main objectives are to:

Reduce direct slag attack;
Reduce molten steel erosion;
Minimize mechanical wear;
Reduce oxidation and decarburization of refractory carbon;
Stabilize the refractory working surface;
Extend BOF campaign life.

In simple terms, the principle is:

Controlled End Slag → Gas Agitation → Slag Splashing → Slag Adhesion → Protective Coating → Longer Converter Life

2. Principle of BOF Slag Splashing

The effectiveness of slag splashing depends mainly on four factors:

End-Slag Control + Gas Agitation + Slag Adhesion + Protective Layer Formation

After steel tapping, a certain amount of end slag remains in the converter. The slag chemistry is adjusted to achieve suitable viscosity, melting behavior, MgO level, and adhesion characteristics.

Nitrogen is commonly used to agitate the slag through the bottom stirring system. The resulting gas flow causes the slag to splash upward and spread across the refractory lining.

As the slag cools and solidifies, it forms a protective coating.

During the following heats, this coating helps protect the refractory lining from aggressive slag, molten steel, oxidation, and mechanical impact.

3. Main BOF Slag Splashing Methods

3.1 Slag Splashing with Highly Oxidizing Slag

When end-point slag has a relatively high oxidation potential, slag conditioning may be required before splashing.

Important slag parameters include:

FeO content;
MgO content;
CaO content;
Slag basicity;
Viscosity;
Temperature;
Slag volume.

Excessive FeO can increase slag aggressiveness toward refractory materials, while excessively high temperature or fluidity may make it more difficult to establish a stable protective coating.

Therefore, the slag splashing process should coordinate:

Slag Chemistry → Slag Temperature → Gas Flow → Splashing Time → Slag Adhesion

With the development of low-slag and double-slag steelmaking, low-slag slag splashing technology has also become an important research and development direction.

4. Key Process Factors for BOF Slag Splashing

4.1 Control End-Slag Composition

End-slag chemistry is one of the most important factors determining slag splashing performance.

Key parameters include:

MgO;
FeO;
CaO;
Basicity;
Viscosity;
Melting temperature;
Slag temperature.

MgO is particularly important because it affects the compatibility between slag and MgO-based refractory materials.

A properly controlled MgO level can reduce the dissolution of MgO-containing refractory materials into the slag.

However, excessive MgO may increase slag viscosity and melting temperature and can negatively affect slag splashing performance.

Therefore, the optimum slag chemistry should be determined according to the steel grade, hot-metal composition, refractory material, and BOF operating conditions.

4.2 Control the Retained Slag Volume

The retained slag volume directly affects the formation of the protective layer.

Too little slag may result in insufficient coating coverage, while excessive slag retention may cause:

Bottom build-up;
Reduced effective furnace volume;
Reduced furnace capacity;
Bottom tuyere blockage;
Reduced gas permeability.

Therefore, retained slag volume should be optimized according to converter capacity, slag condition, blowing practice, and bottom stirring performance.

4.3 Control Tapping Temperature

Tapping temperature directly influences end-slag temperature, which in turn affects the formation and stability of the slag coating.

If slag temperature is too high, the protective coating may remain unstable or partially remelt.

If it is too low, slag fluidity may be insufficient for effective splashing.

Therefore, tapping temperature should be optimized according to downstream LF, RH, VD, or other secondary refining requirements.

5. Influence of Refractory Materials

Slag splashing performance depends not only on slag chemistry but also on refractory material quality.

BOF refractories must withstand:

High temperature;
Slag corrosion;
Molten steel erosion;
Oxidation;
Thermal shock;
Mechanical impact.

Magnesia-carbon bricks are widely used in BOF working linings because of their high refractoriness and resistance to slag attack.

Refractory composition, carbon content, brick structure, and surface condition can all influence slag adhesion and coating stability.

Therefore, a reliable BOF refractory protection strategy should integrate:

Refractory Design + Refractory Selection + End-Slag Control + Slag Splashing Parameters

6. Slag Splashing in Combined-Blown BOF Converters

Combined-blown converters use both top oxygen blowing and bottom gas injection to improve bath mixing and metallurgical reaction efficiency.

The bottom stirring system also plays an important role during slag splashing.

Proper gas flow can improve slag movement and promote more uniform distribution of protective slag on the refractory lining.

However, long-term slag retention and splashing may also cause:

Furnace bottom build-up;
Bottom tuyere blockage;
Slag accumulation;
Reduced effective furnace volume;
Reduced bottom stirring performance.

Therefore, operators should carefully control:

Splashing Time + Retained Slag Volume + Nitrogen Pressure + Gas Flow Rate + Bottom Stirring Intensity

7. Slag Splashing in Small BOF Converters

Small BOF converters may operate under different conditions from large integrated steel plants.

Typical challenges may include:

Greater hot-metal composition fluctuations;
Variable silicon content;
Shorter heat cycles;
Higher tapping temperatures;
Limited secondary refining capacity;
Restricted bottom stirring conditions;
Higher slag temperatures.

These factors make slag splashing process control more challenging.

Therefore, small converters should not simply copy the parameters used by large steel plants. Slag splashing parameters should be developed according to the specific converter design, hot-metal conditions, refractory materials, and production rhythm.

8. Slag Splashing in Semi-Steelmaking Processes

Semi-steelmaking conditions may produce slag compositions that differ from conventional BOF operations.

With appropriate control of MgO, FeO, basicity, slag volume, and splashing parameters, the end slag can be used to form a stable protective layer.

Industrial experience has demonstrated that optimized slag splashing can significantly extend converter campaign life under suitable operating conditions.

However, the actual improvement in campaign life depends on many factors, including converter capacity, hot-metal chemistry, refractory quality, slag practice, bottom stirring, and operator control.

9. Advantages of BOF Slag Splashing

9.1 Longer Converter Campaign Life

The most direct benefit of slag splashing is the extension of refractory campaign life.

A stable protective coating reduces direct exposure of the refractory lining to aggressive slag and molten steel.

9.2 Lower Refractory Consumption

Reduced refractory wear means fewer repair, gunning, and relining operations.

This can lower refractory consumption and reduce maintenance requirements.

9.3 Lower Maintenance Costs

A longer converter campaign can help extend the service interval of equipment associated with converter maintenance.

Maintenance planning can therefore be optimized according to converter campaign condition and equipment status.

9.4 Reduced Manual Maintenance

A stable slag coating can reduce the frequency of manual refractory repair and gunning operations, lowering the workload for steel plant personnel.

9.5 Improved Production Stability

A more stable refractory profile helps maintain effective furnace volume and consistent operating conditions, supporting stable BOF production.

10. Limitations of BOF Slag Splashing

Despite its benefits, slag splashing also has several limitations that need to be carefully managed.

10.1 Furnace Bottom Build-Up

Long-term slag retention and splashing may cause slag accumulation at the furnace bottom.

Severe build-up can reduce effective furnace volume and affect tapping and melting operations.

10.2 Bottom Tuyere Blockage

Slag accumulation can block bottom tuyeres and reduce gas permeability.

This may negatively affect bath stirring and metallurgical reactions.

10.3 More Complex Process Control

Slag splashing performance depends on multiple parameters, including:

End-slag chemistry;
Slag temperature;
Retained slag volume;
Gas pressure;
Gas flow rate;
Splashing time.

Poor control of any of these parameters can result in an unstable or excessively thick protective coating.

10.4 Equipment and Refractory Requirements

The bottom stirring system, furnace body, refractory lining, and gas control system must remain in good operating condition.

Therefore, slag splashing should be integrated with overall BOF equipment maintenance and refractory management.

11. How to Improve BOF Slag Splashing Performance

Steel plants can improve slag splashing performance through several measures.

Optimize End-Slag Chemistry: Control MgO, FeO, CaO, and slag basicity to obtain suitable adhesion and refractory compatibility.
Optimize Retained Slag Volume: Avoid insufficient slag for coating formation while preventing excessive slag accumulation.
Optimize Gas Flow and Splashing Time: Adjust gas pressure, flow rate, and splashing duration according to converter size, slag condition, and bottom stirring capacity.
Select Suitable Refractory Materials: Use appropriate MgO-based refractory materials, such as magnesia-carbon bricks, according to slag chemistry and operating conditions.
Monitor Furnace Bottom Build-Up: Furnace bottom height, refractory thickness, slag accumulation, and bottom gas permeability should be monitored regularly.
Introduce Digital Refractory Management: By integrating campaign data, refractory wear, slag chemistry, bottom stirring parameters, and heat records, steel plants can develop more accurate refractory life prediction and slag splashing optimization systems.

12. Sanrui Electric Furnace: Supporting Efficient Steelmaking Equipment

As a professional electric furnace and metallurgical equipment manufacturer, Sanrui Electric Furnace focuses on the design and manufacturing of EAFs, refining furnaces, and related steelmaking equipment.

For modern steel plants, converter campaign management is not simply a refractory issue. It is a comprehensive engineering system involving:

Furnace Design + Refractory Materials + Bottom Stirring + Slag Control + Automation + Process Management

Stable equipment design, reliable gas control, and optimized metallurgical parameters provide the foundation for longer equipment service life and lower steelmaking costs.

Sanrui Electric Furnace continues to focus on efficient, energy-saving, and intelligent metallurgical equipment solutions, helping steel producers improve equipment reliability, reduce maintenance requirements, and optimize overall production efficiency.

13. Conclusion

BOF slag splashing is an effective technology for extending converter campaign life and reducing refractory consumption.

By controlling end-slag chemistry, retained slag volume, tapping temperature, gas flow rate, and splashing time, steel plants can form a stable protective slag coating on the refractory working surface and reduce refractory attack from high-temperature slag, molten steel, and oxidizing atmospheres.

At the same time, slag splashing must be carefully controlled to avoid problems such as furnace bottom build-up, bottom tuyere blockage, and unstable slag coating formation.

As automation, refractory monitoring, process data analysis, and digital steelmaking technologies continue to develop, BOF slag splashing is expected to move toward more precise control, intelligent monitoring, longer refractory life, and lower steelmaking costs.

As a professional metallurgical equipment manufacturer, Sanrui Electric Furnace will continue to provide reliable steelmaking equipment and technical solutions for modern steel plants, supporting more efficient, stable, and sustainable steel production.

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