With the development of steel smelting technique, there is higher and higher demand on high quality steel. To meet market requirement and clean steel development trend, out-furnace refinery ratio is continuously increasing. Therefore, refractory materials for out-furnace refinery application is developing rapidly.
AOD Furnace Description
AOD furnace is mainly used for stainless steel production. At the beginning, oxygen is blown for oxidized de-carbonization. During oxidization period, slag’s oxidization ability is increasing and temperature can reach to more than 1700℃. Next comes to reduction period, silicon, iron or aluminum is added to reduce chrome in slag, at this period, slag alkalinity is still low. Finally, lime is added to remove sulfur, as desulfurization needs high alkalinity. In the whole smelting process, slag will transform from acid to basic, atmosphere will also change from oxidization to reduction. Because of non-continuous operation, furnace lining temperature is high and has large fluctuation. So AOD furnace lining’s service life is very low, only 30 times or so, by improving smelting condition and gunning patching maintenance, the service life can reach to 70 times or more.
For AOD furnace, earlier, magnesia chrome bricks are widely used. But magnesia chrome bricks requires complicated production craft and ultra high sintering temperature, energy consumption is huge, cost is high, what’s more, magnesia chrome refractory has severe environmental contamination problem, so are gradually replaced bymagnesia calcia bricks.
AOD Furnace Lining Damage Reason
The main damage reasons of AOD furnace lining are: 1) permeation and dissolution corrosion caused by high smelting temperature and long acid slag action time. 2) thermal spalling and structural spalling caused by temperature fluctuation. 3) Fierce gas-slag-steel liquid scouring and erosion. 4) Under changing AOD furnace atmosphere, Cr2O3 and FeOn in magnesia chrome bricks can have oxidization and reduction reaction, which will destroy firebrick’s structure and volume stability.
Tuyere part main damage is thermal spalling and structural spalling, tuyere ambient place mainly suffers eddy and low alkalinity slag corrosion. Slag line’s main damage is high basicity slag permeation caused structural spalling. Furnace bottom’s main damage is high alkalinity slag corrosion and permeation. So, AOD furnace firebricks should have low porosity, high temperature strength, high thermal shock resistance and high slag permeation resistance.
AOD Furnace Lining Refractories
Magnesia calcia bricks have gradually replaced magnesia chrome bricks and are more and more popularly used in AOD furnace linings. Magnesia calcia bricks can be divided into sintered dolomite bricks, pitch binding dolomite bricks, resin binding dolomite bricks and so on. Different grades of dolomite refractory bricks can be used for different parts of AOD furnaces. When smelting temperature is very high, carbon containing refractories will have oxidation and reduction reaction and is not suitable for using. Except for dolomite bricks, magnesia calica lining joint material, magnesia calcia lining gunning mix, magnesia calcia chamotte and so on.
