Steel plants consume more magnesia refractory than any other industry. BOF converters, EAF furnaces, steel ladles, and tundishes - all lined with magnesia-based products. The reason: basic slags generated in steelmaking attack silica and alumina aggressively. Magnesia (MgO) is itself basic, so it resists basic slag dissolution.
But "magnesia refractory" is a broad term covering raw materials, shaped bricks, and castable formulations with significantly different properties. This guide maps the magnesia family clearly, compares the key performance data, and explains which product fits which application.
The Magnesia Family - Four Materials, Four Roles
| Material | Form | Primary Role | MgO Range |
|---|---|---|---|
| Dead Burned Magnesia (DBM) | Raw material / powder | Raw material for shaped bricks and monolithics | 90–96% |
| Fused Magnesia (FM) | Raw material / grain | Premium raw material for high-performance MgO-C | 95–98% |
| Magnesia-Carbon (MgO-C) Brick | Shaped brick | BOF, EAF, ladle slag line | 65–80% MgO + 8–20% C |
| Magnesia-Alumina Spinel Brick | Shaped brick | Cement kiln burning zone, ladle working lining | 60–80% MgO + 10–25% Al₂O₃ |
These four products serve different positions in the production chain. DBM and FM are the raw materials that go into making the bricks. MgO-C brick and spinel brick are the finished lining products that go into your furnace.
MgO Purity Grades: 90%, 95%, 97% - When Each Threshold Matters
Not every application needs 97% MgO. Here's the practical guide:
90% MgO (DBM-90): Standard grade for general backup linings, ladle working lining in lower-demand positions, and monolithic formulations. Fe₂O₃ content typically 1.5–2.5%. Adequate for steelmaking temperatures up to 1650°C. Lowest cost in the magnesia family.
95% MgO (DBM-95 / FM-95): Standard for ladle slag line, BOF backup lining, and EAF bottom. Fe₂O₃ drops to 0.5–1.0%. Bulk density for FM-95: 3.35–3.50 g/cm³. The most widely shipped grade for steelmaking applications.
97%+ MgO (FM-97, FM-98): Required for high-carbon MgO-C brick (15–20% C) where MgO grain quality controls the slag resistance. Fe₂O₃ < 0.3%. FM-97 grain is fully fused - the periclase crystal is larger and denser than DBM, providing superior slag infiltration resistance. Premium: 30–50% over DBM-95.
One clarification worth stating plainly: DBM-95 and FM-95 are not interchangeable at the same price. DBM is calcined; FM is electrically fused. FM has larger periclase crystal size (>1mm vs. 0.3–0.5mm for DBM), lower porosity, and higher bulk density. For MgO-C brick in BOF slag line positions, FM is the correct raw material - using DBM to substitute FM is a quality downgrade that shortens campaign life.
Dead Burned Magnesia vs. Fused Magnesia: Microstructure Difference
The microstructure difference explains the performance difference.
DBM production: Magnesite ore is calcined at 1700–1800°C in a shaft kiln or rotary kiln. The MgO crystal (periclase) size after calcination: 0.3–0.5mm. Some residual porosity from the calcination process. See our dead burned magnesia price and evaluation guide for sourcing reference.
FM production: Magnesite or DBM is melted in an electric arc furnace at 2800°C. The molten MgO solidifies into large single-crystal periclase with crystal size >1mm and extremely low residual porosity (bulk density 3.45–3.55 g/cm³).
Result: FM has significantly higher hot modulus of rupture (HMOR) and lower slag penetration rate under identical test conditions. For high-slag-contact positions - BOF working lining, ladle slag line - this microstructure advantage translates directly to longer campaign life.
We supply both DBM and FM. For every order, we include a COA with crystal size distribution (D50) and bulk density. Ask for it - a supplier who can't provide D50 data on FM grain is not testing what they're shipping.
Magnesia-Carbon Brick vs. Magnesia-Spinel Brick - Application Map
Magnesia-Carbon (MgO-C) Brick
MgO-C brick combines magnesia (65–80% MgO) with graphite carbon (8–20% C) and antioxidants (Al, Si, or MgAl alloy). The carbon phase performs two functions: it acts as a bonding matrix preventing MgO grain from dissolving in slag, and its high thermal conductivity (graphite: 100–200 W/m·K) creates a frozen slag layer at the brick face that self-protects the lining.
Where it's used: BOF converter working lining, EAF side wall (slag zone), steel ladle slag line. The most widely used shaped refractory in steelmaking.
Carbon content selection:
BOF: 15–18% C (high-carbon for maximum thermal conductivity and slag resistance)
EAF slag line: 12–15% C
Ladle slag line: 10–14% C (lower C to avoid carbon pickup in steel)
One honest limitation: MgO-C brick cannot be used in oxidizing atmospheres - the carbon oxidizes above 700°C. For applications with oxidizing gas contact, specify low-carbon or carbon-free magnesia-spinel brick instead.
Magnesia-Alumina Spinel Brick
Magnesia-spinel brick uses MgO as the primary phase with Al₂O₃ additions (10–25%) that form magnesium aluminate spinel (MgAl₂O₄) during firing. The spinel phase improves thermal shock resistance dramatically compared to pure magnesia brick.
Where it's used: Cement kiln burning zone (the most demanding position in cement production), lime kiln, ladle working lining where carbon contamination of steel is prohibited, and non-ferrous furnace linings.
MgO/Al₂O₃ ratio selection:
Cement kiln burning zone: 70/30 (higher spinel content for maximum thermal shock resistance)
Ladle working lining: 80/20 (higher MgO for better slag resistance while maintaining thermal shock resistance)
BOF, EAF, Ladle - Matching Grade to Application
| Application | Zone | Recommended Material | Key Specification |
|---|---|---|---|
| BOF | Working lining | MgO-C brick, 15–18% C | FM-97 grain, CCS ≥35 MPa |
| BOF | Safety lining | DBM-95 brick or castable | Bulk density ≥3.00 g/cm³ |
| EAF | Side wall (slag zone) | MgO-C brick, 12–15% C | FM-95 grain, HMOR ≥8 MPa @1400°C - see electric arc furnace refractory guide |
| EAF | Roof | High alumina or corundum | Al₂O₃ ≥90% for high-temp zone |
| Ladle | Slag line | MgO-C brick, 10–14% C | FM-97 grain, C content matched to steel grade |
| Ladle | Safety/backup | DBM-95 castable | Al₂O₃ + MgO mixed or pure MgO |
| Cement kiln | Burning zone | Magnesia-spinel, 70/30 | PLC ±0.5% at 1650°C |
A steel mill in Turkey was replacing their ladle slag line every 80 heats. After we supplied FM-97-based 12% C MgO-C brick matched to their steel grade (low carbon steel, so we capped carbon at 12%), they reached 130+ heats per campaign. The grade selection - specifically the carbon content limit - was the key change.
For more on extending campaign life, see our steel ladle refractory lining guide.
China Sourcing: What Quality Documentation to Require
For all magnesia refractory materials, request the following before bulk order:
For DBM/FM raw materials:
Chemical analysis: MgO%, CaO%, SiO₂%, Fe₂O₃%, Al₂O₃% (all from XRF)
Bulk density (g/cm³) - measured per ASTM C20
Grain size distribution (D50, D90) - especially critical for FM
Source mine certification (Dashiqiao, China is the dominant quality source)
For MgO-C and Spinel bricks:
COA: composition + physical properties from the production batch, not just "typical values"
HMOR (Hot Modulus of Rupture) @ 1400°C - the critical high-temperature strength indicator
PLC at service temperature
Carbon content verification for MgO-C (some suppliers under-declare carbon to lower cost)
We keep 3-year production records with lot-traceable COAs. For every shipment, the COA accompanies the delivery note.
Frequently Asked Questions
What is the difference between dead burned magnesia (DBM) and fused magnesia (FM)?
DBM is produced by calcining magnesite at 1700–1800°C. FM is produced by electrically fusing magnesite at 2800°C. FM has larger periclase crystal size (>1mm vs. 0.3–0.5mm for DBM), higher bulk density (3.45–3.55 vs. 3.15–3.35 g/cm³ for DBM), and significantly lower slag infiltration rate. FM-97 is the standard raw material for high-performance MgO-C brick in BOF and ladle slag line applications.
What carbon content should I specify for MgO-C brick in a steel ladle?
For ladle slag line MgO-C brick, carbon content is typically 10–14%. Higher carbon (15–18%) is used in BOF where carbon pickup in steel is less critical and maximum thermal conductivity is needed. For low-carbon steel grades, specify 10–12% C maximum to minimize carbon contamination risk. Always tell your supplier the steel grade being produced.
Can magnesia-spinel brick replace MgO-C brick in a BOF?
Not directly. MgO-C brick in BOF relies on the carbon phase for self-protection through the frozen slag layer mechanism. Magnesia-spinel brick doesn't form this protective layer. Spinel brick is better suited for cement kiln applications with oxidizing atmospheres. For BOF, stay with MgO-C.
What does MgO purity level 95% vs. 97% mean in practice?
MgO-90 to MgO-95 are produced from lower-grade raw materials and have higher CaO and SiO₂ impurities. MgO-97 from fused magnesia has minimal impurities and the largest periclase crystal size. The practical difference: at the ladle slag line, a 95% DBM-based brick may last 80 heats; a 97% FM-based brick may last 120–140 heats under the same operating conditions.
