The Role of High Alumina Bricks in Steel Refining
High alumina bricks are shaped refractory products with an alumina content of 48 % or more, and they are a standard furnace wall material in steel refining. They combine high refractoriness with good structural strength and chemical stability, which allows a refining vessel to run at temperature for long campaigns without losing lining thickness in the wall areas.
The choice of a high alumina brick for the furnace wall, rather than a silica or fireclay brick, is normally driven by three requirements: resistance to the ferrous oxide-rich slags that form during refining, volume stability under repeated heating and cooling, and enough hot strength to carry the lining load at working temperature.
Raw Materials and Manufacturing Process
High alumina bricks are produced from a blend of high-purity alumina sources and selected additives. The main components are:
Calcined or fused alumina - the aggregate that provides the alumina content and the volume stability of the finished brick.
Clay or bauxite bond - the plastic fraction that gives the mix its forming behaviour and reacts during firing to bind the aggregate.
Minor additives - small additions used to adjust firing shrinkage, improve the bond or control the porosity of the fired product.
The manufacturing route is a controlled sequence of batching, mixing, pressing, drying and high-temperature firing. Grinding and screening of the aggregate determine the particle packing, which in turn sets the apparent porosity; firing temperature and kiln atmosphere determine the amount of mullite that develops and, with it, the hot strength of the brick.
Grades and Typical Properties
High alumina bricks are graded by alumina content. The values below are typical for dense shaped bricks; acceptance limits follow the applicable product standard or the agreed drawing.
| Grade | Al2O3 min (%) | Apparent porosity max (%) | Cold crushing strength min (MPa) | Refractoriness under load T0.6 min (°C) |
|---|---|---|---|---|
| LZ-48 | 48 | 22 | 40 | 1450 |
| LZ-55 | 55 | 22 | 45 | 1470 |
| LZ-65 | 65 | 23 | 50 | 1500 |
| LZ-75 | 75 | 23 | 55 | 1520 |
| LZ-80 | 80 | 21 | 60 | 1530 |
Bulk density, apparent porosity and cold crushing strength are normally verified to GB/T 2997 and GB/T 5072, and refractoriness under load to GB/T 5989. Higher alumina grades are selected where the slag is more aggressive or where the wall has to carry a heavier load.
Applications in Steel Refining Furnaces
High alumina bricks are applied throughout the refining route, both as working lining and as safety lining:
Furnace walls - the wall area of basic oxygen furnaces and electric arc furnaces, where the brick is protected from the hottest slag line by a basic working lining.
Ladles - ladle walls and bottoms, including the permanent lining behind the working lining and, in some practices, the slag line where a high alumina grade is adequate.
Tundishes - tundish lining and impact areas, where thermal shock resistance and cleanliness of the steel both matter.
Secondary refining units - walls and roofs of degassing and heating stations that need volume stability under repeated thermal cycles.
Torpedo ladles and mixers - high-wear areas where a dense, strong brick resists erosion by moving metal.
One practical point that is often overlooked: the furnace wall brick must be matched to the slag chemistry of the specific refining practice. A high alumina wall performs well against slags with moderate basicity but is attacked more quickly by highly basic, low-viscosity slags, which is why basic bricks are retained at the slag line of the same vessel.
Installation and Service Life Considerations
Use a mortar that matches the brick grade and the service temperature, and keep joints thin and fully filled to avoid slag penetration paths.
Leave the specified expansion allowance; high alumina bricks expand on first heating and the allowance protects the shell from excessive stress.
Follow a controlled dry-out and heat-up curve, because residual water released too quickly causes spalling of the working face.
Keep the brick dry in storage and stack it on clean pallets away from silica dust and from standing water.
Inspect and photograph the lining at each reline so that the wear pattern can be used to adjust the grade selection for the next campaign.
Where the lining is composite, the interface between the high alumina wall and any basic brick should be designed so that the two materials do not react at service temperature; a suitable joint or a compatible intermediate layer avoids spalling at the boundary.
Frequently Asked Questions
Q: What alumina content defines a high alumina brick?
A high alumina brick contains at least 48 % alumina, with commercial grades running from LZ-48 through LZ-55, LZ-65, LZ-75 and LZ-80 as the alumina content rises.
Q: Why are high alumina bricks used for furnace walls in steel refining?
They offer high refractoriness, good cold and hot strength, and volume stability, so the wall holds its shape and thickness through repeated refining cycles.
Q: Can high alumina bricks be used at the slag line of a BOF or EAF?
In most practices the slag line is lined with basic bricks because highly basic slags attack alumina-silicate material; high alumina grades are used where slag basicity and viscosity are moderate.
Q: What properties should be checked on delivery?
Alumina content, apparent porosity, bulk density, cold crushing strength and refractoriness under load, together with dimension tolerances and a visual check for cracks and corner damage.
Q: How does apparent porosity influence performance?
Low porosity limits the penetration of slag and metal into the brick, which slows chemical attack and reduces the risk of spalling of the working face.
Q: What is the difference between high alumina bricks and fireclay bricks?
Fireclay bricks contain less than 48 % alumina and have lower refractoriness and hot strength; high alumina bricks provide a higher service temperature and better resistance to ferrous slags.
