Analysis of the Causes and Solutions of "Garlic-like" Erosion of Carbon Bricks in Blast Furnace Cylinders
In the blast furnace ironmaking process, the carbon bricks in the dead iron layer of the furnace cylinder often suffer from shortened service life due to "garlic-like" erosion. This phenomenon has become a key bottleneck restricting the overall campaign life of blast furnaces.
This paper draws on typical cases such as the 1,260 m³ blast furnace at Handan Steel and the 4,063 m³ blast furnace at Baosteel. It systematically elaborates on solutions from three dimensions: erosion mechanisms, material optimization, and process control. The goal is to provide the industry with a practical technical path that can be implemented effectively.
01 Explanation of the Causes of "Garlic-Like" Erosion
1.1 The Fatal Effect of Missing Slag Skin
In the area above the centerline of the tap hole in the furnace cylinder, liquid slag covers the inner wall and forms a stable slag skin, which effectively prevents direct contact between molten iron and carbon bricks. However, in the dead iron layer region, due to the long-term accumulation of molten iron, slag cannot settle and form a protective layer.
Data from Handan Steel show that the hot face temperature of carbon bricks in the dead iron layer is 200–300 °C higher than in the area above the tap hole. This temperature difference between the interior and exterior triggers thermal stress of 15–20 MPa, far exceeding the shear strength limit of the carbon bricks and causing ring-shaped cracking.
1.2 Mechanical Scouring by Iron Ring Flow
Numerical simulations indicate that, during iron tapping, high-speed circulation forms between the dead material column and the furnace cylinder sidewall, with flow velocities reaching 3–5 m/s. Monitoring of the Baosteel 4,063 m³ blast furnace revealed that the abrasion rate of carbon bricks 1.5 m below the tap hole reached 0.8 mm/month-three times higher than in other areas. This circulating scouring increases the surface roughness of carbon bricks from Ra6.3 μm to Ra25 μm, accelerating molten iron penetration.
1.3 Chemical Erosion by Alkali Metals
Potassium and sodium oxides in the blast furnace burden react with carbon bricks at temperatures above 1,200 °C to form K₂CO₃ and Na₂CO₃, with volume expansion rates of 120% and 150%, respectively. Post-operation examination of WISCO Blast Furnace No. 5 revealed that the porosity of carbon bricks in the alkali erosion zone increased from 18% to 35%, while compressive strength dropped by 40%, forming a brittle layer up to 200 mm deep.
02 Innovative Breakthroughs at the Material Level
2.1 Microporous Carbon Brick Technology
The hot-pressed microporous carbon bricks developed by UCAR (United States) control pore sizes within the range of 0.1–1 μm by optimizing the raw material particle size distribution (d₅₀ = 5 μm) and applying a molding pressure of 300 MPa. Laboratory tests show that the depth of iron penetration in this material is 82% lower than that of conventional carbon bricks, and the residual strength retention rate after a 1,500 °C thermal shock test reaches 92%.
2.2 Ceramic Cup Composite Structure
Nippon Steel (Japan) developed an Al₂O₃–SiC ceramic cup with a thermal conductivity of 8 W/(m·K), which helps establish an isothermal zone at 1,150 °C on the hot face of the carbon bricks. As a result, the 800 °C embrittlement zone is shifted into the interior of the ceramic cup. After Baosteel adopted this technology, the service life of the furnace cylinder increased from 8 years to 15 years, and the cost of refractory materials per ton of iron was reduced by 0.8 yuan.
2.3 In-Situ Protection Using Titanium Oxide
During blast furnace protection operations, Handan Iron and Steel increased the TiO₂ content in slag to 15%, promoting the formation of a dense Ti(C,N) protective layer on the surface of the carbon bricks. SEM analysis shows that this protective layer reaches a thickness of up to 3 mm and a hardness of up to HV2000, effectively resisting erosion from molten iron infiltration. Following implementation of this technology, the erosion rate of carbon bricks was reduced from 1.2 mm/month to 0.3 mm/month.
03 Precision in Process Control
3.1 Optimization of Dead Iron Layer Depth
The optimal depth of the dead iron layer can be determined by establishing a hydrodynamic model, which allows for the calculation of the critical depth required to ensure stable furnace operation and minimize brick erosion.
3.2 Intelligent Regulation of the Cooling System
The dynamic cooling control technology developed by Shougang Jingtang Company monitors the furnace's temperature field in real time using a matrix of thermocouples embedded inside the carbon bricks at 200 mm intervals. When the temperature at any point exceeds 1,150 °C, the system automatically increases the cooling water flow by 20%, maintaining the carbon brick working temperature within the range of 900–1,050 °C. This technology reduces fluctuations in the furnace cylinder's thermal load from ±15% to ±5%.
3.3 Optimization of Furnace Protection Operation System
A four-phase model has been established for titanium ore–based furnace protection:
Pretreatment phase: Gradually increase slag TiO₂ content to 8%.
Rapid film-forming phase: Maintain TiO₂ at 12–15% for 72 hours.
Stable protection phase: Control TiO₂ content within 10–12%.
Decay monitoring phase: Measure the thickness of the protective layer weekly.
After implementing this system, Anshan Iron & Steel extended the effective furnace protection period from 45 days to 90 days and reduced titanium ore consumption by 0.5 kg per tonne of iron produced.
04 Verification of Effectiveness in Typical Cases
4.1 Baosteel 4,063 m³ Blast Furnace
After adopting the integrated technology of ceramic cup + microporous carbon bricks + intelligent cooling, the service life of the furnace cylinder has surpassed 20 years. The ceramic cup structure has reduced heat loss by 30%, the microporous carbon bricks have decreased molten iron permeability by 75%, and the intelligent cooling system has achieved a temperature control accuracy of ±3 °C.
4.2 1,260 m³ Blast Furnace of Handan Iron & Steel
By implementing dead iron layer optimization and titanium oxide furnace protection, the issue of "garlic-like" erosion was successfully eliminated. The residual thickness of carbon bricks in the furnace cylinder increased from 300 mm to 650 mm. As a result, the annual maintenance cost was reduced by 12 million RMB, and the blast furnace productivity increased by 0.2 t/(m³·d).
05 Technology Development Trend Outlook
With the advancement of Industry 4.0, blast furnace protection technology is exhibiting three major trends:
Material Composites: Developing silicon carbide–graphite composite carbon bricks that balance thermal conductivity and erosion resistance.
Intelligent Monitoring: Applying fiber-optic grating sensing technology to enable real-time imaging of the carbon brick stress field.
Maintenance Prediction: Establishing an erosion prediction model based on digital twin technology to provide risk warnings up to six months in advance.
Through the synergistic efforts of material innovation, process optimization, and intelligent control, the industry's persistent problem of "garlic-like" erosion of carbon bricks in blast furnaces is being effectively addressed. In the future, with the deep integration of ultra-high-temperature materials and artificial intelligence technologies, blast furnace longevity will enter a new stage of development.