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In the harsh production environment of the metallurgical industry, slag chutes and steel launders are two core pieces of equipment responsible for directing high‑temperature molten materials. One guides molten slag, the other conveys molten steel – both directly withstand continuous scouring and erosion by high‑temperature slag and liquid steel. Their performance directly affects the continuity, safety, and overall cost of the production line.
However, because they look similar and operate under comparable conditions, many practitioners easily confuse them. This article provides a comprehensive analysis of the key differences and selection criteria for slag chutes and steel launders from four perspectives: function, material selection, structural design, and maintenance.
1. Slag Chute vs. Steel Launder – A Single Word Makes a World of Difference
What Is a Slag Chute?
A slag chute (also called a slag runner) is equipment used in metallurgical engineering to convey molten slag. It receives liquid furnace slag discharged from metallurgical furnaces (such as flash smelting furnaces, electric furnaces, converters, etc.) and directs it to a granulation system or slag treatment facility for further processing. Slag chutes operate in an environment of 800–1200°C slag flow and are indispensable auxiliary equipment in steelmaking and ironmaking processes.
What Is a Steel Launder?
A steel launder (also called a casting chute) is a flow‑directing device used to guide and convey high‑temperature molten steel. It receives molten steel from converters, electric furnaces, or ladles and directs it to the tundish or mould of a continuous caster. Steel launders face even more extreme conditions – the instantaneous temperature of poured steel can exceed 1500°C, demanding exceptional thermal‑shock resistance from the material.
Key Differences at a Glance
| Aspect | Slag Chute | Steel Launder |
|---|---|---|
| Conveyed medium | Liquid slag (containing SiO₂, Al₂O₃, etc.) | High‑temperature molten steel (clean liquid steel) |
| Operating temperature | 800–1200°C | Above 1500°C (instantaneous impact) |
| Primary failure modes | Wear, erosion, deformation | Thermal‑shock cracking, steel contamination |
| Critical performance requirements | Wear resistance, slag corrosion resistance | Thermal‑shock resistance, non‑contamination of steel |
| Surface finish requirement | Moderate | Ra ≤ 12.5 μm (to prevent steel contamination) |
2. Core Functions of Slag Chutes and Steel Launders
Core Functions of a Slag Chute
1. Receiving and directing molten slag
The slag chute is the first passage for furnace slag discharge. During converter tapping, the slag chute must withstand liquid slag at around 1500°C and guide it from the furnace mouth to the slag pot or granulation system.
2. Protecting the furnace lining and equipment
A high‑quality slag chute effectively resists erosion and scouring of the inner wall, ensuring smooth steelmaking and extending lining life.
3. Coordinating with slag treatment processes
In slag treatment processes such as the rotary drum method and air granulation, the slag chute is the core channel that receives and directs liquid steel slag into the treatment equipment. Its high‑temperature and wear‑resistant properties directly determine treatment efficiency and equipment maintenance intervals.
Core Functions of a Steel Launder
1. Guiding high‑temperature molten steel
On the continuous‑casting platform or during steel transfer, the steel launder is responsible for directing high‑temperature molten steel or treated slag from the ladle to the mould or tundish.
2. Withstanding thermal shock and thermal cycling
The steel launder must withstand the impact and thermal shock of liquid steel, ensuring process continuity and stability. The severe temperature changes during pouring impose extremely high demands on the launder’s resistance to thermal cracking.
3. Avoiding steel contamination
The surface finish and material purity of the steel launder directly affect steel quality. A rough surface or impure material may introduce impurities into the steel, degrading the final product quality.
3. Material Selection – How to Choose the Right Slag Chute and Steel Launder?
Material selection is the primary decision in designing slag chutes and steel launders. Because their operating temperatures and medium characteristics differ, material choices also emphasise different properties.
Common Materials for Slag Chutes
| Material Grade | Max. Service Temp. | Key Characteristics | Typical Applications |
|---|---|---|---|
| ZG35Cr28Ni10 | 1000–1300°C (peak 1400°C+) | High Cr (~28%) and Ni (8–11%), excellent wear and corrosion resistance | Converter slag tapping, high‑temperature slag conveying |
| ZG35Cr28Ni8 | 1200°C | Strong high‑temperature deformation resistance, cost‑effective | Continuous scouring by high‑temperature slag |
| ZG40Cr25Ni20Si2 (2520/310S) | 1050–1150°C (peak 1200°C) | Si‑strengthened oxidation resistance, dense oxide film | Electric‑arc furnace metallurgy, rotary‑kiln slag guidance |
| GX40CrNiSi25-20 (1.4848) | 1050–1150°C | European standard heat‑resistant steel, equivalent to 2520 | Export projects or EU‑standard requirements |
| Heat‑resistant ductile iron (RQTSi4Mo) | Medium‑high temp. | Lower cost | Medium‑to‑low temperature slag conveying |
ZG35Cr28Ni10, with its high chromium content (approximately 28%) , forms a dense chromium‑oxide protective film that effectively resists abrasive wear and various corrosive media in molten slag. The high nickel content (8–11%) provides excellent high‑temperature strength and thermal‑fatigue resistance.
ZG35Cr28Ni8 meets the demands of many high‑temperature, high‑wear applications while offering greater cost competitiveness – a cost‑performance choice.
Common Materials for Steel Launders
Steel launders face instantaneous thermal shock above 1500°C, demanding even more stringent thermal‑shock resistance and high‑temperature strength:
| Material Grade | Key Characteristics | Typical Applications |
|---|---|---|
| ZG40Cr25Ni20Si2 (2520) | Excellent overall performance, good thermal‑shock resistance | Standard choice for continuous‑casting launders |
| ZGCr25Ni20 | Typical heat‑resistant cast steel | Conventional steel launders |
| High‑alloy heat‑resistant steel | Higher Ni/Cr content, stronger temperature resistance | Ultra‑high‑temperature conditions |
| Copper‑water‑jacket launder | Water‑cooled medium enhances high‑temperature performance | High‑temperature slag/steel guidance (copper smelting, etc.) |
It is particularly important to note that steel launders require extremely high surface quality – the roughness of the steel‑contact surface must reach Ra ≤ 12.5 μm to prevent slag adhesion and contamination of the liquid steel.
Three‑Step Material Selection Guide
Step 1: Identify the medium
- Conveying molten slag → choose a slag chute, prioritise wear‑ and corrosion‑resistant materials (ZG35Cr28Ni10 / Ni8)
- Conveying molten steel → choose a steel launder, prioritise thermal‑shock‑resistant, high‑purity materials (2520 series)
Step 2: Determine the temperature
- ≤1000°C → heat‑resistant ductile iron or ZG35Cr28Ni8
- 1000–1200°C → ZG35Cr28Ni10 or 2520
- 1200–1300°C → ZG35Cr28Ni10 (peak conditions) or high‑alloy heat‑resistant steel
- Above 1500°C (instantaneous) → 2520 series or copper‑water‑jacket structure
Step 3: Consider special requirements
- Strong acidic slag corrosion → prioritise 2520 (Si‑strengthened oxidation resistance)
- High abrasion conditions → prioritise ZG35Cr28Ni10 (high‑chromium wear resistance)
- Frequent start‑stop (thermal fatigue) → prioritise materials with excellent thermal‑fatigue resistance
4. Structural Design and Manufacturing Processes
Common Structural Types
Integral cast launder: Manufactured as a single piece using lost‑foam casting or investment casting, with no welded joints. The inner wall is dense, free of porosity, blowholes, or shrinkage. Compared with traditional segmented welded structures, integral casting greatly reduces the risk of weld cracking at high temperatures.
Composite launder: The most severely impacted areas are lined with more wear‑resistant ceramic materials or given special heat treatment to create a graded protective layer. Composite slag chutes use a magnesia‑ or high‑alumina‑based substrate combined with a graphite flow‑surface layer, with mechanical interlocking to enhance durability.
Modular and quick‑change type: A replaceable launder body design allows the worn section to be quickly pulled out like a “drawer” and replaced with a new module, greatly shortening maintenance downtime.
Brick‑lined launder: Prefabricated and assembled on site, significantly reducing the manufacturing lead time and lowering both production and installation/dismantling costs.
Copper‑water‑jacket launder: In non‑ferrous metallurgy, water‑cooled copper launders replace traditional refractory or graphite launders, using water cooling to enhance high‑temperature performance.
Manufacturing Process Comparison
| Process | Key Advantages | Suitable Applications |
|---|---|---|
| Lost‑foam casting | One‑piece forming, no welds, smooth inner wall prevents slag adhesion | High‑quality slag chutes / steel launders |
| Investment casting | High dimensional accuracy, good surface quality | Small batches, high precision requirements |
| Sand casting | Low cost, suitable for large castings | Large‑volume production, conventional conditions |
| Copper‑water‑jacket structure | Water cooling raises temperature limit | Ultra‑high‑temperature non‑ferrous smelting |
Key Design Considerations
1. Uniform wall thickness transition
Cast launders must have smooth wall‑thickness transitions to avoid local stress concentrations that lead to high‑temperature cracking.
2. Inner‑wall smoothness
The flow channel wall should maintain a high degree of smoothness to prevent slag adhesion and material build‑up. For steel launders, surface finish requirements are stricter (Ra ≤ 12.5 μm).
3. Thermal expansion allowance
Launders expand at high temperatures; the design must include adequate expansion clearances to avoid deformation from compression.
4. Swing launder design
The “swing launder” introduced by MCC Jingcheng enables precise receiving and guiding of liquid steel even as the ladle car moves, improving operational flexibility and safety.
5. Application Scenarios and Typical Operating Conditions
Typical Applications of Slag Chutes
| Application | Operating Characteristics | Recommended Material |
|---|---|---|
| Converter slag tapping | 1500°C liquid slag scouring | ZG35Cr28Ni10 |
| Electric‑arc furnace smelting | Continuous high‑temperature slag discharge | 2520 series |
| Flash furnace / electric furnace slag conveying | Large slag volume, high slag temperature | Copper‑water‑jacket launder |
| Steel slag treatment system | Rotary drum, air granulation processes | ZG35Cr28Ni8 / Ni10 |
| Blast‑furnace auxiliary slag runner | Auxiliary directing and distribution | Heat‑resistant steel launder |
Typical Applications of Steel Launders
| Application | Operating Characteristics | Recommended Material |
|---|---|---|
| Continuous‑casting platform | Directing steel to the mould | 2520 series |
| Steel transfer | Ladle‑to‑tundish guidance | High‑alloy heat‑resistant steel |
| Converter feed chute | Adding dephosphorisation / desulphurisation materials | Wear‑ and heat‑resistant steel |
6. Selection Guide – Five Steps to the Best Solution
Step 1: Identify the conveyed medium
- Molten slag → Slag chute
- Molten steel → Steel launder
Step 2: Determine the temperature range
- Conventional high temperature (≤1200°C) → ZG35Cr28Ni8 (economical) or ZG35Cr28Ni10 (high performance)
- Ultra‑high temperature (1200°C+) → ZG35Cr28Ni10 or 2520 series
- Instantaneous 1500°C+ → 2520 series or copper‑water‑jacket structure
Step 3: Evaluate wear and corrosion
- Severe wear (high SiO₂/Al₂O₃ content) → high‑chromium material (ZG35Cr28Ni10)
- Strong corrosion (acidic slag) → 2520 (Si‑strengthened oxidation resistance)
- General conditions → ZG35Cr28Ni8 (cost‑effective)
Step 4: Choose the manufacturing process
- High quality, long service life → lost‑foam casting
- Fast delivery, controlled cost → sand casting
- Ultra‑high‑temperature special conditions → copper‑water‑jacket structure
Step 5: Consider maintenance convenience
- Quick‑change requirement → modular / replaceable launder design
- Conventional maintenance → integral cast launder
7. Usage and Maintenance Highlights
Failure Modes and Prevention
1. Wear
Hard particles such as SiO₂ and Al₂O₃ in the slag cause rapid wear. Preventive measures: select high‑chromium wear‑resistant materials (ZG35Cr28Ni10), or line the most severely worn areas with wear‑resistant ceramics.
2. Thermal‑fatigue cracking
Alternating heating and cooling from frequent start‑stop cycles can lead to cracking. Preventive measures: choose materials with excellent thermal‑fatigue resistance and subject castings to high‑temperature stress‑relief annealing before delivery.
3. Deformation
Long‑term load at high temperatures can cause launder distortion. Preventive measures: choose materials with strong high‑temperature deformation resistance (e.g., ZG35Cr28Ni8) and design appropriate wall thicknesses and reinforcing structures.
4. Slag adhesion and blockage
Rough inner walls promote slag build‑up. Preventive measures: maintain high inner‑wall smoothness and clean regularly.
Routine Maintenance Points
- Regular inspection: Check the inner wall for wear, cracks, or deformation.
- Timely replacement: Replace immediately when severe wear or cracks are found to avoid leakage accidents.
- Clean slag deposits: Regularly remove slag adhered to the inner wall to keep the flow path clear.
- Check connections: Inspect the sealing at the joint between the launder and the furnace outlet.
Measures to Extend Service Life
- Select high‑quality heat‑resistant steel: Compared with ordinary carbon steel, high‑quality heat‑resistant steel launders offer 2–3 times longer service life.
- Optimise the casting process: Use lost‑foam casting to eliminate welded weak points.
- Local reinforcement: Line the most severely impacted areas with wear‑resistant ceramics or hard‑face with high‑temperature materials.
- Modular design: Adopt a replaceable design so that only the damaged module needs changing after local wear.
- Intelligent monitoring: Integrate sensors to monitor wall‑thickness wear and internal temperature in real time, enabling predictive maintenance.