31
subota
siječanj
2026
Wear Mechanisms and Wear Reasons of Slide Gate Plates in Steelmaking Operations
In secondary metallurgy and continuous casting, the slide gate system is an indispensable flow-control component that ensures stable, adjustable, and safe discharge of molten steel from the ladle or tundish. At the heart of this system lie the slide gate plateshigh-performance refractory components engineered to withstand extreme thermal, mechanical, and chemical stresses. Their wear behavior directly affects casting stability, steel cleanliness, ladle lining life, and operational safety. Understanding the fundamental wear mechanisms of slide gate plates is therefore essential for metallurgists, refractory engineers, and plant operators aiming to optimize performance and minimize casting disturbances.
This article provides a detailed examination of the wear reasons for slide gate plates, covering thermomechanical factors, chemical attack, operational variables, design issues, and material-specific behavior.
slide gate plate
1. Overview of the Slide Gate Plate Function
Slide gate plates control the flow of molten steel through a moving plate system. The typical configuration includes:
Upper nozzle (seat brick / collector nozzle)
Upper plate (fixed plate)
Lower plate (sliding plate)
Nozzle or ladle shroud connection
These plates are typically manufactured using high-purity alumina-carbon, alumina-zirconia-carbon (AZC), spinel-carbon, or in some cases, alumina-graphite composites. Their operational environment exposes them to temperatures exceeding 1600°C, high hydraulic pressure from molten steel, mechanical sliding friction, oxidation, and severe thermal gradients.
Given these harsh conditions, slide gate plates exhibit several characteristic wear forms, each driven by a distinct physical or chemical mechanism.
2. Major Wear Mechanisms in Slide Gate Plates
Slide gate plates are subjected to combined thermo-chemical-mechanical stresses, which lead to the following primary wear mechanisms:
2.1 Erosive Wear from Molten Steel Flow
One of the dominant wear mechanisms is hydrodynamic erosion. When the slide gate opening is adjusted, molten steel accelerates through a restricted nozzle area. The high-velocity flow impacts the refractory surface, causing:
Micro-fracture of alumina grains
Progressive removal of carbon binder
Scouring of the plate surface, especially near the bore
High turbulence at partial openings or during casting speed changes increases erosive wear significantly.
2.2 Corrosive Slag Attack
burned slide gate plate
During ladle operations, slag infiltration into the plate microstructure causes:
Decarbonization of the carbon matrix
Reaction between AlO and basic slag components
Softening and weakening of the refractory structure
In steel grades with high oxygen activity, slag-metal emulsions form at the plate surface, accelerating corrosion.
2.3 Oxidation of the Carbon Matrix
Carbon is a key component for thermal shock resistance and strength. However, carbon oxidation occurs due to exposure to:
High temperature air on the plate exterior
Oxygen present in molten steel at early casting stages
Atmospheric oxygen entering through microcracks
Oxidation reduces plate density and cohesion, weakening its structure and making it more susceptible to mechanical and erosive wear.
2.4 Mechanical Abrasion from Plate Sliding
During operation, plates slide against each other under high pressure via a hydraulic system. Mechanical wear results from:
Friction between the plate surfaces
Particle detachment at microscopic asperities
Potential misalignment causing localized wear grooves
This abrasion is unavoidable but can be mitigated by material selection and lubrication practices.
2.5 Thermal Shock Damage
Every preheat-to-casting cycle imposes extreme thermal gradients:
Preheating reaches 10001100°C
External surfaces cool when exposed to air
Molten steel contact produces rapid temperature spikes
These fluctuations cause microcracking, spalling, and structural fatigue. Thermal shock damage becomes more pronounced if:
Preheat temperatures are inconsistent
Plates are quenched by contact with cold air or water
Casting delays allow excessive cooling between heats
2.6 Mechanical Impact and Compression Failure
Slide gate plates experience intense mechanical loads:
Hydraulic pressure from clamping
Steel hydrostatic load from ladle weight
Shock from plate opening/closing dynamics
Rigid, brittle refractories like high-alumina plates are especially vulnerable to localized crushing near bolt seats or around the nozzle bore.
3. Detailed Reasons for Slide Gate Plate Wear
While the mechanisms describe how wear happens, operational and design parameters clarify why plates degrade. Below are the principal reasons behind excessive or premature wear.
3.1 High Oxygen Levels in Molten Steel
The oxidation potential of the molten steel is a major factor influencing plate wear. High oxygen levels cause:
Graphite oxidation at the plate bore
Increased viscosity and aggressiveness of tundish slag
Greater inclusion formation and deposition
These reactions degrade the carbon matrix, exposing alumina grains to irregular failure.
3.2 Aggressive Slag Compositions
The chemical nature of slag impacts slide gate longevity:
High FeO and MnO levels intensify corrosion
Basic slags attack alumina-rich plates
Fluoride-containing fluxes promote grain boundary melting
Slag infiltration leads to softening, destabilization, and surface erosion.
3.3 Casting Speed and Flow Rate Instability
Operational variability, such as changes in casting speed, affects flow dynamics:
High-speed flow increases erosion
Partial opening creates turbulent eddies
Sudden throttling causes pressure surges and mechanical shock
These conditions heavily influence plate bore enlargement and surface scouring.
3.4 Misalignment of the Slide Gate Assembly
Even minor misalignment causes uneven distribution of mechanical load, leading to:
Localized abrasion
Shear-induced microcracking
Uneven bore wear and leakage pathways
Misalignment is one of the most common causes of premature failure in poorly maintained or worn ladle gates.
3.5 Inadequate Preheating or Overheating
Temperature management is critical. Problems occur when:
Preheat is too short thermal shock at first metal contact
Preheat is excessive carbon oxidation and structural weakening
Heating is non-uniform internal stress gradients
Ideal preheating ensures refractory stability while minimizing oxidation.
3.6 Poor Plate Material Selection
Different steel grades and casting conditions require specific plate formulations:
Basic oxygen steelmaking (BOF) heats require high corrosion resistance
Ultra-low carbon steels demand high purity AZC plates
High-cleanliness grades need plates with low porosity and anti-clogging additives
Using a mismatch leads to accelerated wear, bore choking, or plate failure.
3.7 Mechanical Overloading or Incorrect Clamping Force
The hydraulic system must maintain precise clamping pressure. Excessive pressure causes:
Localized crushing
Plate warping
Internal cracking
Insufficient pressure produces metal leakage and increased frictional wear during sliding.
3.8 Inclusion Deposition and Nozzle Clogging
Transitory inclusion buildup contributes to:
Localized thermal stress
Flow instability
Increased turbulence and erosion downstream
Inclusion deposition accelerates wear near the nozzle outlet and slide gate bore.
3.9 Interruption or Delay in Casting
Casting stops or delays cause plates to:
Cool unevenly
Accumulate slag crusts
Crack due to thermal cycling
Restarting casting after long delays often produces the highest wear rates.
4. Microstructural Factors Influencing Wear
Slide gate plates are engineered materials whose performance is tied to their microstructure. Wear behavior is heavily influenced by:
4.1 Grain Size and Bonding
Finer alumina grains improve strength, while coarse grains enhance erosion resistance. Poor bonding leads to grain pullout under flow.
4.2 Porosity
High porosity easier slag penetration rapid degradation.
4.3 Carbon Quality and Quantity
Graphite flake size and distribution determine resistance to thermal shock. Lower carbon reduces oxidation problems but compromises toughness.
4.4 Additives (Zirconia, Spinel, SiC)
These enhance corrosion resistance and high-temperature strength. Poor additive dispersion results in localized weaknesses.
5. Preventive Strategies to Reduce Slide Gate Plate Wear
Optimizing plate life requires a multi-disciplinary approach:
Control slag chemistry, minimizing FeO and aggressive fluxes
Optimize preheating cycles to reduce thermal stress
Ensure precise alignment of slide gate mechanisms
Use appropriate refractory materials based on steel grade
Maintain stable casting speeds and avoid sudden throttling
Improve tundish metallurgy to reduce inclusion clogging
Monitor hydraulic clamping pressures and maintain even loading
Implement real-time temperature and wear tracking
Plants combining these strategies typically extend plate life by 2040%.
6. Conclusion
Slide gate plate wear is a complex phenomenon driven by the interaction of molten steel flow, slag chemistry, thermal gradients, oxidation, mechanical loading, and operational variability. Understanding the wear mechanismserosion, corrosion, oxidation, abrasion, thermal shock, and mechanical stressis essential for diagnosing failure modes and implementing effective mitigation strategies.
By combining optimal refractory design, precise operational control, and disciplined maintenance practices, steel plants can significantly improve slide gate plate performance, enhance casting stability, and reduce production costs. As steelmaking progresses toward cleaner steel, tighter tolerances, and higher productivity, the importance of advanced slide gate materials and controlled operating environments will continue to grow.
Oznake: slide gate plate, sliding plate, slide gate
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29
četvrtak
siječanj
2026
Submerged Entry Shroud in Steelmaking: Mechanisms, Degradation, and Clean Steel Control
1. Introduction
In modern continuous casting and secondary steelmaking operations, maintaining steel cleanliness between the ladle and tundish is of critical importance. One of the most essential refractory components serving this function is the Submerged Entry Shroud (SES), also referred to as the sub entry shroud or ladle-to-tundish shroud. The SES provides a protected flow channel for molten steel, preventing reoxidation, minimizing inclusion formation, and stabilizing steel flow.
Although the submerged entry shroud is often considered a passive refractory component compared with the submerged entry nozzle (SEN), recent experimental and industrial studiesparticularly those focusing on decarburization, oxidation, and clogging mechanismshave demonstrated that the internal condition of the shroud plays a decisive role in downstream steel quality and nozzle performance. Many of the degradation phenomena identified for SENs are directly transferable to SES behavior, especially regarding carbon oxidation, coating interactions, and steelrefractory reactions.
This article presents a comprehensive technical discussion of the sub entry shroud, grounded in the scientific insights provided by the referenced experimental work, with particular attention to material degradation, internal surface reactions, and their influence on clean steel production.
2. Function and Position of the Submerged Entry Shroud
The sub entry shroud is installed between the ladle slide gate or stopper system and the tundish inlet nozzle. Its main functions are:
Preventing molten steel contact with atmospheric oxygen and nitrogen
Suppressing reoxidation reactions
Reducing temperature loss
Minimizing turbulence and slag entrainment
Protecting downstream refractory components (tundish nozzle, SEN)
The SES typically operates under the following conditions:
Steel temperature: 15501650 °C
Strong thermal gradients during preheating and start-up
Exposure to oxidizing gases during preheating
Long contact times with liquid steel
These conditions make the SES highly vulnerable to chemical and structural degradation, particularly at the internal bore surface.
3. Materials Used in Sub Entry Shrouds
3.1 Typical Material Systems
Most sub entry shrouds are manufactured from AlOC, MgOC, or ZrO-containing AlOC refractories. Carbon is intentionally added to:
Improve thermal shock resistance
Reduce steel wettability
Enhance spalling resistance
However, as demonstrated in the learned article, carbon is also the weakest link under oxidizing conditions.
3.2 Role of Carbon in Shroud Degradation
Carbon oxidation begins at temperatures as low as 873973 K, particularly during preheating in oxygen- or CO-containing atmospheres. Once carbon is oxidized:
Open porosity increases
Oxygen diffusion accelerates
Steel penetration becomes possible
Chemical reactions with steel intensify
This decarburization phenomenon, extensively studied for SENs, is equally relevant for SESs.
4. Decarburization of Sub Entry Shrouds
4.1 Mechanism of Decarburization
The decarburization of SES refractories occurs primarily during preheating and standby periods, when the shroud is exposed to hot oxidizing gases. The reaction can be simplified as:
C (solid) + O / CO CO / CO (gas)
As shown in the referenced study:
Initial decarburization is reaction-controlled
Later stages are diffusion-controlled
Porosity and pore connectivity dominate oxidation kinetics
Once the internal surface loses carbon, it becomes chemically active, increasing its affinity for molten steel and inclusions.
5. Influence of Internal Coatings on Sub Entry Shroud Performance
5.1 Conventional Glass and Silicon-Based Coatings
Glass or silicon powder coatings are often applied to SESs to protect carbon during preheating. While these coatings can temporarily reduce oxidation, experimental evidence indicates several negative effects:
Alkali-rich glass penetrates refractory pores
Reaction with graphite generates CO gas
Local pressure buildup causes microcracking
Inhomogeneous coating thickness leads to uneven protection
These effects mirror the coating-related issues observed in SENs and explain why coated SESs may still contribute to cleanliness problems.
5.2 Formation of Reactive Internal Surfaces
Once coatings degrade or infiltrate the refractory matrix, the SES internal surface can transform into:
Alkali-rich reaction layers
Silicate phases
Decarburized alumina-rich zones
Such surfaces act as nucleation sites for inclusion attachment, even before steel reaches the SEN.
6. Interaction Between Sub Entry Shroud and Molten Steel
6.1 Reoxidation and Inclusion Formation
If the SES fails to provide complete sealing, atmospheric oxygen may enter the steel stream, causing:
Formation of AlO inclusions
Growth of complex oxides
Increased inclusion loading entering the tundish
These inclusions later contribute to nozzle clogging, a phenomenon often incorrectly attributed only to the SEN.
6.2 REM-Alloyed Steels and Shroud Reactivity
The learned article demonstrates that steels containing rare earth metals (REM) are particularly sensitive to refractory interactions. In SESs with decarburized or coated internal surfaces:
REM elements reoxidize rapidly
REM oxides adhere to refractory walls
Initial accretion layers form upstream of the SEN
Thus, the SES can act as the first stage of the clogging process, not merely a transport channel.
7. Accretion and Deposit Formation Inside Sub Entry Shrouds
Although less severe than in SENs, deposit formation inside SESs has been observed, especially during long casting sequences. These deposits consist of:
Oxide-rich layers near the refractory wall
Steel-enriched solidified phases
Reaction products derived from coatings
Such deposits increase flow resistance and promote turbulent flow into the tundish, indirectly affecting mold-level stability.
8. Thermal Shock and Mechanical Damage
Sub entry shrouds experience:
Rapid heating during steel opening
Localized cooling during flow interruptions
Mechanical stresses from assembly and alignment
If decarburization has already weakened the matrix, thermal shock can cause:
Internal cracking
Spalling of the bore surface
Accelerated erosion during casting
This mechanical degradation further exposes fresh reactive surfaces.
9. Engineering Strategies for Improving Sub Entry Shroud Performance
9.1 Atmosphere Control During Preheating
Based on experimental findings:
Oxygen content in preheating gas must be minimized
Short, high-temperature preheating is preferable
Long low-temperature holding should be avoided
These measures significantly reduce carbon oxidation.
9.2 Advanced Coating Technologies
The article demonstrates that YSZ (yttria-stabilized zirconia) coatings, applied via plasma-based processes, offer substantial advantages:
Chemically inert surface
High resistance to steel and REM reactions
Effective barrier against oxygen diffusion
Smooth internal bore surface
Although more expensive, such coatings represent a promising future direction for SES design.
9.3 Material Optimization
ZrO-containing AlOC systems show improved oxidation resistance
Antioxidants such as ZrSi provide volumetric expansion upon oxidation, sealing pores
Optimized carbon content balances thermal shock resistance and oxidation risk
10. Role of the Sub Entry Shroud in Clean Steel Production
From a systems engineering perspective, the sub entry shroud must be viewed as an active metallurgical component, not a simple refractory pipe. Its internal condition directly influences:
Steel reoxidation behavior
Inclusion population entering the tundish
Downstream SEN clogging
Overall casting stability
Failures or degradation at the SES stage often propagate through the entire casting process.
11. Educational Significance for Engineering Students
For engineering students, the SES provides a valuable case study in:
High-temperature materials degradation
Multiphase chemical reactions
Interaction between process design and materials selection
Importance of upstream control in complex metallurgical systems
Understanding SES behavior reinforces the concept that clean steel production begins before the tundish and mold.
12. Conclusion
The submerged entry shroud plays a far more critical role in steelmaking than traditionally assumed. Experimental and industrial evidence shows that decarburization, coating degradation, and refractorysteel interactions inside the SES can significantly affect steel cleanliness and casting performance. Many phenomena previously attributed solely to SEN clogging originate, at least in part, within the SES.
By applying advanced materials, optimized preheating practices, and improved coating technologies, the SES can be transformed from a vulnerability into a robust barrier protecting steel quality. For modern steelmaking, a scientifically informed approach to sub entry shroud design and operation is essential. More information please visit Henan Yangyu Refractories Co.,Ltd
Oznake: sub entry shroud, SES, sub entry nozzle
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