The main chemical components of magnesium-calcium refractory materials are MgO and CaO, and the main phases are cristobalite and Calcite, which brings together the advantages of MgO and Ca0.
Compared with magnesium-chromium refractory materials, the magnesium-calcium-based refractory materials used in AOD furnace lining are:
(1) The raw material resources are rich, the price is low, and it does not contain chromium, so it will not increase the chromium inclusion in the molten steel. It is very important to control not only chromium-free steel liquid but also chromium content of chromium-containing steel liquid.
(2) The main components MgO and CaO have high melting points (2800℃ and 2570℃, respectively), low vapor pressure and stable thermodynamic properties.
(3) The MgO-CaO combination has a larger two-sided angle than the MgO-MgO combination, which is beneficial to improve the resistance to slag permeability and resistance to slag corrosion. The thermal shock resistance of magnesium-calcium-based materials is better than that of magnesium-chromium-based materials.
(4) Magnesium-calcium-based materials are very resistant to oxidation and reduction, even in AOD furnaces and at high temperatures.
(5) Magnesium-calcium-based materials exhibit obvious creep properties at temperatures as low as 1260°C. It shows that this kind of material has strong resistance to spalling on the hot surface, so it can become a dense material with maximum corrosion resistance when used.
(6) The magnesium-calcium refractory contains highly reactive f-CaO (free calcium oxide can repair the cracks of this type of material and form a very dense impervious working surface, so it has a very high Corrosion resistance.
(7) The presence of f-CaO can purify molten steel, and is especially suitable for smelting pure steel.
In recent years, with the rapid development of steelmaking technology, as one of the important refractory materials for the steel industry, magnesium-calcium refractory materials have been used in steelmaking, continuous casting tundish, refining furnace, especially in smelting special steel and pure steel It is far superior to other refractory materials.
Magnesia-calcium refractory materials are mainly used in converters at the bottom of the furnace, the molten pool and the front and rear surfaces. Since the 1960s, China has developed a variety of magnesia dolomite fired bricks and implemented a variety of magnesium-calcium refractory composite furnaces on the converter, which has achieved good results and improved the furnace age of the converter. Increased steel production. In the late 1980s, my country began to use a large number of magnesia-carbon bricks, which made magnesium-calcium-based refractories subject to strong impact. It is undeniable that magnesia-carbon bricks are a more excellent refractory material, but compared with them, magnesium-calcium refractory materials also have certain advantages: it is low in price, generally 1/3~1/2 of magnesia-carbon bricks , CaO in this material reacts with SiO2 in the slag to produce high-melting-point minerals 2CaO·SiO2 and 3CaO·SiO2, which makes the slag thick and easily forms a slag layer on the lining, thereby protecting the lining and also making the lining working surface more It is easy to stick together with the furnace repair material, which improves the furnace repair effect. The synthetic magnesium dolomite clinker and fired oil-immersed brick developed in my country have formed a scale.
For a long period of time, magnesium-calcium materials are still used in certain parts of the converter, such as the bottom of some converters, the front and rear two large surfaces and other parts that erode light and easy to repair the furnace. Now, although magnesium-calcium-based refractories are basically not used on the lining, CaO-containing spray repair materials and front and rear large-scale repair materials are gradually being expanded.