Blast furnaces are essential equipment in the ironmaking process, exposed to extreme temperatures of 1400°C-1600°C, molten iron, high pressure (1.5-3.0 bar), and corrosive slag. Refractory bricks play a critical role in ensuring the integrity of the furnace lining, increasing campaign life, and maintaining safe and efficient iron production. This guide outlines the types of refractory bricks used in different zones of the blast furnace, their performance requirements, and selection guidelines to ensure optimal material choice for long-lasting operation.
Hearth & Bottom (Core Zone – Molten Iron Contact)
The hearth is the critical area where molten iron is in direct contact with the refractory lining. It must withstand molten iron temperatures of 1500°C-1600°C, high hydrostatic pressure, and carbon dissolution, requiring refractory bricks that resist erosion and penetration.
Refractory Brick Types & Applications
Carbon Bricks: Semi-graphitic carbon bricks (fixed carbon ≥90%) and graphite bricks provide high thermal conductivity and resist iron and carbon penetration.
Magnesia-Carbon Bricks: For the sidewalls of the hearth, magnesia-carbon bricks (MgO ≥85% + C 10-15%) offer excellent resistance to slag erosion and iron penetration.
Insulation Layer: Ceramic fiber boards and high-alumina insulating bricks retain heat and enhance energy efficiency.
Key Performance Parameters
Max service temperature: 1650°C
Compressive strength: ≥60MPa
Iron penetration resistance: ≥98%
Linear shrinkage: ≤0.1% (1500°C for 5 hours)
Industry Backing
Used in over 50 large blast furnaces (φ5-6m) worldwide.
Campaign life extended to 12-15 years, compared to 6-8 years with ordinary bricks
Bosh & Belly (High-Wear & Thermal Shock Zone)
The bosh and belly are exposed to temperatures of 1200°C-1400°C, with high-speed gas scouring, iron ore charging impacts, and thermal shock from temperature fluctuations. Refractory bricks in these zones must have high mechanical strength, thermal shock stability, and wear resistance.
Refractory Brick Types & Applications
High-Alumina Bricks: High-alumina bricks (Al₂O₃ 75-85%) and magnesia-alumina spinel bricks (Al₂O₃ 70% + MgO 15%) provide excellent mechanical strength and thermal shock stability.
Wear-Resistant Bricks: High-alumina bricks with added SiC (5-10%) offer superior resistance to charging impact and gas scouring.
Key Performance Parameters
Thermal shock cycles: ≥35 times (1100°C → 20°C)
Wear resistance: ≥95%
Slag erosion rate: ≤0.15mm/h
Compressive strength: ≥80MPa
Industry Backing
Case study: A Chinese 5000m³ blast furnace reduced bosh brick replacement by 60% using spinel-enhanced high-alumina bricks
Shaft (Mid-Temp & Erosion Zone)
The shaft experiences temperatures between 800°C-1200°C, where gas-solid reactions occur, causing moderate thermal shock and low-to-medium slag erosion. Refractory bricks here should be cost-effective while providing moderate temperature resistance and wear resistance.
Refractory Brick Types & Applications
Medium-High Alumina Bricks: Medium-high alumina bricks (Al₂O₃ 60-70%) and fire clay bricks offer excellent cost-effectiveness and moderate temperature resistance.
High-Alumina Bricks: High-alumina bricks (Al₂O₃ 70-75%) provide enhanced wear and erosion resistance in the lower shaft near the bosh.
Key Performance Parameters
Max service temperature: 1300°C
Thermal shock cycles: ≥30 times
Acid/alkali resistance: ≥95%
Compressive strength: ≥60MPa
Industry Backing
Used in 50+ blast furnace shafts, reducing maintenance frequency from twice per year to once every two years.
Throat & Stack (Low-Temp & Abrasion Zone)
The throat and stack experience lower temperatures of 400°C-800°C, where abrasion from iron ore/coke charging and flue gas corrosion are primary concerns. Refractory bricks in this area need to resist wear and provide thermal insulation.
Refractory Brick Types & Applications
Throat Lining: Heat-resistant castables and high-alumina bricks (Al₂O₃ 50-60%) provide wear resistance and ease of maintenance.
Upper Stack: Fire clay bricks and insulating bricks are cost-effective and provide thermal insulation.
Key Performance Parameters
Max service temperature: 900°C
Wear resistance: ≥90%
Compressive strength: ≥50MPa
Thermal conductivity: ≤0.8W/(m·K)
Ultra-High Temperature & Iron/Slag Resistance
Blast furnace refractories must withstand temperatures above 1400°C and resist molten iron and alkaline slag erosion.
Quantitative Standards
Max service temperature: ≥1400°C (shaft), ≥1650°C (hearth)
Slag erosion rate: ≤0.15mm/h
Iron penetration depth: ≤5mm (1000h test)
Industry Value
Ensures long campaign life, avoiding furnace shutdowns due to refractory failure.
High Mechanical Strength & Wear Resistance
Refractories in high-wear zones such as the bosh and belly must resist abrasion from iron ore charging and high gas velocity scouring.
Quantitative Standards
Compressive strength: ≥60MPa (shaft), ≥80MPa (bosh)
Wear resistance: ≥95% (ISO standard)
Industry Value
Reduces brick spalling and replacement frequency, lowering maintenance costs.
Excellent Thermal Shock Stability
The blast furnace’s operation involves significant temperature fluctuations, and refractories must resist cracking under these conditions.
Quantitative Standards
Thermal shock cycles: ≥30-35 times (1100°C → 20°C)
No cracking after 50+ cycles
Industry Value
Prevents unplanned shutdowns due to thermal stress-induced damage.
Low Permeability & Structural Integrity
Refractories in the hearth and bosh must prevent molten iron, slag, and gas from penetrating the furnace shell to ensure safety.
Quantitative Standards
Apparent porosity: ≤15%
Gas permeability: ≤1×10⁻¹⁴ m²
No structural cracks after high-pressure testing
Industry Value
Ensures furnace safety, preventing shell overheating and leakage risks.
Step 1: Match to Blast Furnace Zone & Operating Conditions
Hearth/Bottom: Carbon bricks/graphite bricks (high temperature + iron resistance)
Bosh/Belly: High-alumina/spinel bricks (wear + thermal shock resistance)
Shaft: Medium-high alumina bricks (cost-effective + mid-temperature resistance)
Throat: Fire clay bricks (low temperature + abrasion resistance)
Step 2: Evaluate Campaign Life & Operating Conditions
For long campaign life (≥10 years), use high-purity carbon and magnesia-carbon bricks.
For high-pressure operations (≥2.5 bar), opt for high-strength spinel bricks.
For frequent start-stop operations, select thermal shock-resistant high-alumina bricks.
Step 3: Prioritize Safety & Compliance
Ensure compliance with ASTM C155/ISO 8895 standards.
Verify iron penetration resistance for hearth bricks and high-pressure impact resistance for bosh bricks.
Our refractory bricks for blast furnaces are trusted by over 100 global steel mills, including ArcelorMittal and Baosteel. With over 30 years of experience, our solutions are backed by comprehensive safety certifications and third-party test reports.
To get a customized solution for your blast furnace (specifying volume, zone, and operating conditions), contact our ironmaking refractory specialist directly for a free technical datasheet or quotation.
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