Understanding the Thermal and Chemical Demands of EAF and BOF Service
Electric arc furnaces (EAF) and basic oxygen furnace (BOF) converters represent the harshest refractory service environments in the steel industry. Steel bath temperatures routinely reach 1,620–1,720°C, with localized hot spots at the slag line, tap hole, and electrode delta zones pushing refractory surfaces to 1,750°C and beyond. Simultaneous attack from basic FeO-rich slags (FeO content 15–30% in BOF slag, up to 40% in EAF flat-bath phases), thermal cycling between heats, and mechanical erosion from scrap charging collectively determine brick life. For plant operators targeting a specific refractory consumption (SRC) below 1.5 kg/t steel in BOF service or below 2.0 kg/t in EAF service, material selection is the single highest-leverage variable. This guide walks through zone-by-zone selection logic, material specifications, and maintenance practices that ThermalEast's product range is engineered to support.
Zone-by-Zone Material Selection for BOF Converters
BOF linings are zoned by severity of wear. A common mistake is specifying a single brick grade across the entire vessel, which results in either over-engineering low-wear zones (unnecessary cost) or under-engineering high-wear zones (premature failure). The table below maps zones to recommended materials and target properties.
| Converter Zone | Primary Wear Mechanism | Recommended Product | Key Spec Targets |
|---|---|---|---|
| Slag Line (Trunnion Area) | FeO slag corrosion, thermal shock | Magnesia-Carbon Brick (standard) | MgO ≥ 78%, C 14–18%, BD ≥ 3.05 g/cm³ |
| Charge Pad / Impact Zone | Mechanical abrasion, spalling | Magnesia-Carbon Brick (high-carbon grade) | MgO ≥ 75%, C 18–22%, CCS ≥ 40 MPa |
| Barrel / Cylindrical Section | Mild slag corrosion, oxidation | Magnesia-Carbon Brick Low-Carbon | MgO ≥ 80%, C 5–10%, antioxidants Al + Si |
| Tap Hole Surround | Steel flow erosion, oxidation | Fused Magnesia Brick | MgO ≥ 97%, fused grain, BD ≥ 3.12 g/cm³ |
| Bottom / Tuyere Block | CO gas erosion, thermal fatigue | Magnesia Brick 95 | MgO ≥ 95%, AP ≤ 18%, RUL ≥ 1,600°C |
ThermalEast's standard magnesia-carbon brick uses fused magnesia aggregate with graphite flake additions and an antioxidant package (typically metallic aluminum 1–2% + silicon carbide or boron carbide) to resist oxidative decarburization at the hot face. The magnesia-carbon-brick-low-carbon grade, with 5–10% C, is specifically engineered for barrel sections where lower thermal conductivity is acceptable and where slag composition is less aggressive — this grade significantly reduces CO emissions during blowing and is increasingly specified in ESG-conscious steelworks.
EAF Lining Design: Electrode Delta, Slag Line, and Side Wall
EAF linings face a fundamentally different wear profile than BOF converters. The electrode delta zone experiences electromagnetic stirring effects, arc flare, and scrap pileup. Sidewalls see cyclic oxidation-reduction from slag foaming practice. The hottest zones regularly exceed 1,700°C during flat-bath operation.
Electrode Delta and Hot Spots
This zone demands the highest-performance magnesia-carbon brick available. Specify MgO ≥ 78%, C 16–20%, with a bulk density ≥ 3.05 g/cm³ and cold crushing strength (CCS) ≥ 40 MPa. ThermalEast's standard magnesia-carbon brick manufactured from large-crystal fused magnesia (grain size ≥ 3 mm dominant fraction) provides the combination of slag resistance and thermal shock tolerance required here. Brick dimensions are typically 230 × 115 × 65 mm standard, or custom-profiled for curved delta sections. Target lining thickness at the delta is 500–700 mm for a modern 100–150 t EAF.
Slag Line and Upper Side Wall
Slag foaming practice — the key lever for energy efficiency in modern EAF operations — dramatically increases slag/brick contact time. Foam slag FeO content ranges from 20–35%. The magnesia-carbon-brick-low-carbon grade (MgO ≥ 80%, C 6–8%) performs reliably in this zone when a slag-coating program is maintained. Lower carbon content reduces the driving force for carbon dissolution into the slag, while the retained graphite network maintains thermal conductivity and thermal shock resistance. For shops running ultra-high-power (UHP) operation above 600 kWh/t, revert to standard carbon grades in the upper slag line.
Back Wall and Taphole Frame
The EAF back wall and taphole surround see direct steel flow and high FeO activity during tapping. Fused magnesia brick (MgO ≥ 97%, fired with fused grain aggregate) outperforms sintered-grain products here due to its dense, low-porosity microstructure (apparent porosity ≤ 14%). ThermalEast's magnesia-brick-fused grade provides the combination of high refractoriness under load (RUL T₀.₅ ≥ 1,680°C) and resistance to basic slag penetration that the taphole environment demands.
Gunning and Hot Repair: Extending Heat Life Between Relining Campaigns
No lining selection strategy is complete without a gunning and maintenance protocol. In both EAF and BOF operations, targeted hot gunning of worn zones — typically after every 50–100 heats in EAF and 300–500 heats in BOF — can extend overall campaign life by 20–35% and dramatically reduce SRC.
- Material: ThermalEast's gunning-mix-magnesia is formulated with reactive MgO and sintered magnesia aggregate, a hydraulic and chemical bond system, and plasticizers for optimal gunning consistency. MgO content ≥ 80%, with a refractoriness of 1,750°C+.
- Application temperature: Hot gunning is effective when lining surface temperature is 200–800°C. Below 200°C, bond development is slow; above 800°C, rebound loss increases sharply.
- Build thickness: Single-pass application should not exceed 50–75 mm to avoid slumping. Successive passes after partial sintering allow build-up to 150 mm in severe wear pockets.
- Water/gun ratio: Typically 8–12% water addition at the gun nozzle. Adjust for ambient humidity and surface condition.
- Zone priority: Focus gunning on the electrode delta and slag-line hot spots first. BOF converters should prioritize the trunnion zone and charge pad.
A well-executed gunning program integrated with systematic thickness measurement (laser profiling or manual gauging every 50 heats) is the foundation of any SRC reduction initiative. Plants reporting SRC below 1.2 kg/t in BOF operations universally cite systematic hot repair as a key practice.
Practical Recommendations Summary
- Use zoned lining design — do not specify a single brick grade across the full vessel.
- Specify fused magnesia aggregate bricks (MgO ≥ 97%) at tap hole surrounds and high-FeO-exposure zones to maximize slag resistance.
- Adopt low-carbon MgO-C grades in lower-wear zones to reduce cost and carbon footprint without sacrificing campaign life.
- Implement a slag coating or slag splashing protocol after each heat to protect the worn lining and reduce gunning frequency.
- Establish lining thickness monitoring at 50-heat intervals; trigger gunning when any zone drops below the minimum safe thickness (typically 200 mm in EAF, 300 mm in BOF).
- Maintain slag basicity (CaO/SiO₂) at 3.0–4.0 in BOF operation; slag outside this range accelerates brick attack regardless of brick quality.
- Use magnesia-brick-95 (MgO ≥ 95%, sintered) for bottom and permanent lining applications where a cost-effective, chemically stable base is required beneath the working lining.
Request a Tailored Material Recommendation from ThermalEast
ThermalEast supplies the full range of magnesia-carbon bricks, fused magnesia bricks, high-purity sintered magnesia bricks, and magnesia-based gunning mixes to EAF and BOF operators across Southeast Asia, the Middle East, and Europe. Our technical team can review your furnace geometry, heat size, scrap mix, slag practice, and current SRC data to recommend a zoned lining specification and gunning protocol matched to your specific operation. Contact ThermalEast today to request a quote, technical datasheet package, or site consultation with our refractory engineers.