1. Introduction

The tundish metering nozzle TMN), also referred to as the tundish nozzle or metering nozzle insert, is a critical functional refractory used in continuous casting operations. Installed at the bottom of the tundish, it controls molten steel flow into the submerged entry nozzle (SEN) or directly into the mold, depending on the casting configuration. The performance and service life of the tundish metering nozzle directly influence casting stability, steel cleanliness, sequence length, productivity, and operational safety.

In modern steelmaking, increasing casting speed, longer casting sequences, higher steel cleanliness requirements, and aggressive steel grades place increasingly severe demands on tundish metering nozzles. Premature failure caused by erosion, corrosion, clogging, thermal shock, or structural cracking can lead to flow instability, steel breakout, unplanned tundish changes, and significant economic losses.

Therefore, improving the service life of tundish metering nozzles is a key technical objective for steel plants and refractory suppliers alike. This article systematically analyzes failure mechanisms and provides practical, engineering-oriented strategies to extend tundish metering nozzle life from the perspectives of material selection, structural design, manufacturing process, steel chemistry control, tundish operation, and quality management.

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2. Failure Mechanisms of Tundish Metering Nozzles

Understanding failure mechanisms is the foundation for life improvement.

2.1 Chemical Corrosion

Molten steel and slag aggressively attack nozzle materials, especially under high oxygen activity and high CaO–Al₂O₃ slag systems. Typical corrosion mechanisms include:

• Dissolution of Al₂O₃ or ZrO₂ into slag

• Chemical reaction between steel inclusions and refractory phases

• Flux penetration into open pores and grain boundaries

High-Mn, high-Ti, ultra-low carbon (ULC), and calcium-treated steels exacerbate corrosion.

2.2 Erosion by Molten Steel Flow

High casting speed increases molten steel velocity at the nozzle bore, resulting in:

• Mechanical erosion of the working surface

• Enlargement of bore diameter

• Loss of flow control accuracy

Localized turbulence and asymmetric flow further intensify wear.

2.3 Nozzle Clogging

Clogging is one of the most severe life-limiting factors and is mainly caused by:

• Deposition of Al₂O₃ inclusions

• Reaction between steel and nozzle material

• Reoxidation products formed at steel–air interfaces

Clogging reduces effective bore diameter, disturbs flow, and often forces premature nozzle replacement.

2.4 Thermal Shock and Structural Cracking

Rapid temperature changes during preheating, start casting, ladle change, or emergency shutdown can induce:

• Thermal stress cracking

• Spalling

• Interfacial delamination in composite nozzles

2.5 Mechanical Damage and Assembly Issues

Improper installation, misalignment, or excessive tightening can introduce mechanical stress, leading to early fracture or leakage.

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3. Optimization of Raw Material Selection

3.1 High-Purity Zirconia-Based Materials

ZrO₂-based materials are widely used due to their excellent corrosion resistance and low wettability to molten steel.

Key optimization points include:

• ZrO₂ content ≥ 75–90% in the working layer

• Low impurity levels (SiO₂, Fe₂O₃ < 0.3%)

• Controlled grain size distribution for dense packing

High-purity zirconia significantly improves resistance to slag corrosion and steel erosion.

3.2 Stabilized Zirconia Systems

Pure zirconia undergoes phase transformation, causing volume expansion and cracking. Stabilizers are essential.

Common stabilizers:

• CaO-stabilized ZrO₂ (CSZ)

• MgO-stabilized ZrO₂ (MSZ)

• Y₂O₃-stabilized ZrO₂ (YSZ)

Optimized stabilizer content improves thermal shock resistance while maintaining corrosion resistance.

3.3 Composite Material Design

Multi-layer or composite structures are increasingly adopted:

• ZrO₂-rich inner bore for corrosion and clogging resistance

• Al₂O₃-based outer body for strength and cost control

• Gradual transition layers to reduce thermal stress

Composite designs balance performance and economic efficiency.

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4. Structural Design Optimization

4.1 Bore Geometry Optimization

The internal bore design has a decisive influence on nozzle life.

Recommended approaches:

• Smooth, streamlined bore profiles

• Optimized entry and exit angles to reduce turbulence

• Avoid sharp corners and sudden cross-section changes

These measures minimize erosion and inclusion deposition.

4.2 Enlarged Working Layer Thickness

Increasing the thickness of the ZrO₂ working layer at high-wear zones significantly extends service life, especially for long sequence casting.

4.3 Sleeve-Type and Composite Bore Structures

Advanced designs include:

• Sleeve-type bore inserts with ultra-high ZrO₂ content

• Replaceable bore sleeves

• Direct composite casting of different materials

These designs localize wear and delay catastrophic failure.

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5. Manufacturing Process Control

5.1 Fine Powder Processing and Homogeneous Mixing

Uniform microstructure is critical. Key controls include:

• High-energy mixing or co-milling

• Narrow particle size distribution

• Uniform stabilizer dispersion

Poor mixing leads to weak zones prone to corrosion and cracking.

5.2 High-Pressure Forming

Isostatic pressing or high-pressure uniaxial pressing:

• Increases green density

• Reduces open porosity

• Improves mechanical strength

Dense microstructures resist slag penetration and erosion.

5.3 Optimized Sintering Regime

Sintering temperature and holding time must be precisely controlled:

• Insufficient sintering leads to high porosity

• Over-sintering causes grain coarsening and thermal shock sensitivity

Controlled sintering ensures optimal density and microstructural stability.

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6. Anti-Clogging Technology

6.1 Low-Wettability Surface Design

Reducing steel and inclusion adhesion is essential.

Methods include:

• High ZrO₂ content

• Addition of anti-wetting phases

• Surface densification treatment

6.2 Calcium Treatment Compatibility

Proper coordination between steel calcium treatment and nozzle material prevents excessive Al₂O₃ buildup.

Refractory composition must match steel chemistry to avoid adverse reactions.

6.3 Inert Gas Purging Optimization

Argon purging through the nozzle:

• Suppresses inclusion deposition

• Stabilizes flow

• Reduces reoxidation

However, excessive gas flow can increase erosion and turbulence. Precise control is critical.

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7. Tundish Operation and Process Control

7.1 Proper Preheating Practice

Uniform and sufficient preheating:

• Eliminates moisture

• Reduces thermal shock

• Improves initial casting stability

Rapid or uneven heating is a common cause of early cracking.

7.2 Stable Casting Conditions

Avoiding abrupt changes in:

• Casting speed

• Steel temperature

• Argon flow rate

Stable conditions significantly reduce thermal and mechanical stress on the nozzle.

7.3 Slag Management

Maintaining appropriate tundish slag composition and thickness:

• Protects nozzle surface

• Reduces oxidation

• Minimizes chemical attack

Low-reactivity, low-FeO slags are preferred.

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8. Quality Control and On-Site Management

8.1 Incoming Inspection of Nozzles

Key parameters to inspect:

• Chemical composition

• Bulk density and porosity

• Bore geometry accuracy

• Surface defects

Strict inspection prevents hidden quality risks.

8.2 Installation Accuracy

Proper alignment and sealing:

• Prevent steel leakage

• Avoid mechanical stress concentration

• Ensure uniform wear

Installation procedures should be standardized and operator-trained.

8.3 Post-Use Analysis and Feedback

Analyzing used nozzles provides valuable insights:

• Wear pattern analysis

• Corrosion depth measurement

• Clogging morphology observation

Feedback supports continuous product optimization.

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9. Future Development Trends

Future improvements in tundish metering nozzle life will focus on:

• Nano-structured and ultra-dense zirconia materials

• Functionally graded materials (FGM)

• Smart nozzles with real-time wear monitoring

• Customized nozzle designs for specific steel grades

Integration of material science, fluid dynamics, and digital control will further enhance nozzle performance.

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10. Conclusion

Improving the service life of tundish metering nozzles is a multidisciplinary engineering challenge involving refractory materials, structural design, manufacturing technology, steelmaking process control, and operational discipline. By systematically addressing corrosion, erosion, clogging, thermal shock, and mechanical damage, steel plants can significantly extend nozzle life, stabilize casting operations, and reduce production costs.

In practice, the most effective approach is not a single technical measure, but an integrated solution combining high-quality refractory materials, optimized nozzle design, precise manufacturing, compatible steel chemistry, and disciplined tundish operation. Continuous collaboration between steelmakers and refractory suppliers is essential to achieve long-term, sustainable performance improvements.

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