Submerged arc furnaces (SAFs), widely used in ferroalloy, chemical, and special materials industries, operate as the “high-temperature core” of production. They run continuously under 1500–2200°C extreme temperatures, severe chemical erosion, intense thermal shock, and heavy mechanical load. The selection and application of refractory materials directly determine furnace service life, operating stability, energy efficiency, and maintenance costs.
This article analyzes the refractory configuration for four major SAF zones—furnace bottom, furnace wall, furnace roof, and tap / slag outlet, combining real industrial data, material performance, and engineering best practices to help achieve long-life, low-maintenance furnace operation.
The furnace bottom bears static pressure of molten burden (up to several MPa), 1600–1800°C thermal shock, and severe erosion by molten metal and slag. A single failure may cause bottom burn-through, leading to catastrophic furnace damage. Therefore, SAF furnace bottoms use a three-layer system—insulation layer, transition layer, working layer—to balance thermal management, erosion resistance, and structural integrity.
Lightweight bricks with bulk density ≤1.0 g/cm³ and thermal conductivity ≤0.25 W/(m·K) are used to reduce heat loss to the foundation.
For example, in a 75,000 kVA FeSi furnace, replacing clay insulation with lightweight bricks reduced the bottom shell temperature from 150°C to 80°C, saving over 120,000 RMB in annual electricity cost.
Using ≥75% Al₂O₃ high alumina bricks with cold crushing strength ≥80 MPa and refractoriness under load ≥1600°C helps buffer thermal and mechanical stresses between the insulation and carbon brick layers, preventing delamination or cracking caused by mismatch in thermal expansion.
Carbon materials are the “ultimate defense” against molten penetration.
Graphite carbon bricks feature bulk density ≥1.75 g/cm³, flexural strength ≥25 MPa, and thermal conductivity ≥40 W/(m·K). At 1500°C, their wetting angle with molten iron exceeds 140°, effectively preventing metal infiltration.
Self-baking carbon bricks → economical for smaller SAFs
Fired carbon bricks → stable performance, widely used
Graphite / microporous carbon bricks → ideal for large and long-campaign furnaces (≥125,000 kVA)
A steel plant using microporous carbon bricks extended furnace bottom life from 2 to 4.5 years, reducing shutdown repairs by six times annually.
Traditional clay-brick furnace bottoms last <1 year and suffer molten iron penetration leading to the well-known “rising bottom” issue.
The three-layer carbon brick system eliminates this, enabling long-term stability and safe furnace operation.
The furnace wall experiences extreme radial thermal gradients (1800°C inside vs. ambient temperature outside), molten burden abrasion, and chemical erosion by furnace gas. A three-layer structure—working layer, intermediate layer, insulation layer—is used to match temperature distribution and stress gradients.
Magnesia-alumina spinel bricks (MgO-Al₂O₃)
Exceptional thermal shock resistance: withstand ≥20 cycles of 1100°C water quenching without cracking. Ideal for SiMn furnaces with severe temperature fluctuations.
Grade-1 High Alumina Bricks (Al₂O₃ ≥ 85%)
CCS ≥100 MPa, RUL ≥1700°C, effective against lime and coke attack in CaC₂ furnaces.
Special High Alumina Bricks
With Cr₂O₃ additions for Ni-Fe furnaces operating near 2000°C, extending wall life by 50%.
These bricks absorb stress between the working layer and insulation layer, preventing crack propagation and blocking slag/gas migration.
The combined insulation system keeps the shell temperature below 60°C.
A FeMn factory reported 20% reduction in wall heat loss and annual natural gas savings of 80,000+ m³ after upgrading the insulation system.
FeSi / FeMn furnaces → prioritize thermal shock resistance → spinel bricks are preferred
CaC₂ furnaces → heavy chemical attack → high alumina + anti-slag coatings are common
Traditional furnace walls fail due to monolithic material selection. Layered design solves cracking and large-area spalling, extending wall life from 1.5 years to 3–4 years.
SAF roofs (arched or flat) require materials that balance lightweight construction, thermal shock resistance, and easy installation. Therefore, roof castables are widely used as the main insulation layer.
High-alumina castable with Al₂O₃ ≥60%, particle size 0–3 mm for flowability, setting time 4–6 hours for on-site workability. After 1100°C firing, compressive strength ≥30 MPa and ≥15 thermal shock cycles (1100°C water quench).
Compared to clay bricks, castables form a monolithic structure with better sealing and fewer joints, greatly reducing heat leakage.
An acetylene plant (CaC₂ furnace) replaced bricks with castables, extending roof life from 8 months to 24 months and increasing CO gas recovery rate from 60% to 75%.
Using a “formwork – casting – curing – baking” process, heating rate must be ≤15°C/h to prevent cracking.
Highland Refractory installation teams can shorten the roof construction cycle by 30%.
Brick roofs suffer from joint cracking, heat leakage (>100°C shell temperature), and short life. Castables deliver long-life performance, better sealing, and easier installation.
Tap holes endure >1800°C molten iron/slag, high-velocity flow (2–3 m/s), and severe chemical erosion. Refractory materials for this zone must offer unmatched anti-erosion performance.
Made with fused corundum aggregate and phosphate/phosphate-bonded binder, CCS ≥15 MPa and ≤0.5% linear change at 1500°C.
Densified structure ensures resistance to molten metal penetration and slag erosion.
Si₃N₄-Bonded SiC
Mohs hardness ≥9, excellent thermal shock resistance (≥30 water-quench cycles at 1000°C)
Used in the erosion-sensitive sections of the tap channel.
Semi-Graphite / Graphite Blocks
Maximize resistance to molten penetration, prevent choking and build-up.
A Ni-Fe plant using a “corundum castable + Si₃N₄-SiC” combination extended tap-hole life from 1 month to 3 months, reducing shutdowns by 12 times/year and increasing Ni-Fe output by 2000+ tons annually.
Traditional clay bricks deteriorate rapidly under extreme erosion, causing frequent shutdowns. High-performance corundum + carbon-based materials create a durable and stable tap system that remains aligned with overall furnace life.
Each zone of the submerged arc furnace requires precision-engineered refractory materials:
Furnace bottom → carbon bricks for anti-penetration
Furnace wall → multi-layer design for anti-thermal shock
Furnace roof → lightweight monolithic castables
Tap hole → corrosion-resistant corundum & SiC composites
Only through coordinated material design can the furnace achieve long-campaign, low-maintenance operation.
Customized engineering solutions for FeSi, FeMn, CaC₂, Ni-Fe, and other SAF types
Full-cycle services from manufacturing to on-site installation and after-sales supervision
Cost optimization through extended furnace life, reduced downtime, and energy-saving insulation systems
As the industry moves toward long-life, energy-saving, and environmentally friendly refractory solutions (e.g., pitch-free carbon bricks, low-porosity castables), selecting a supplier with strong R&D and installation capabilities is essential to achieving competitive advantage.
The main raw materials of magnesia carbon bricks include fused magnesia or sintered magnesia, flake graphite, organic bonds and antioxidants.
High melting point basic oxide magnesium oxide (melting point 2800℃)
High alumina fine powder is a powder material with alumina (Al2O3) as the main component.
