Engineering implementation of enhanced furnace count
The smelting process and operational studies have shown that, when the bath temperature is above 1700e, the etch rate of the refractory material is increased by 1 time for each 50e increase. When AOD smelts stainless steel, the temperature of the molten pool in the decarburization period is about 1750e, and the lining refractories work at high temperatures for a long time, and the refractories are required to have high high temperature strength.
In addition, according to the characteristics of AOD refining, it is required that the refractory material should have high slag corrosion resistance and thermal shock resistance. Therefore, the refractory material should have low impurity, high content of main crystalline phase, and dense microstructure. The choice of furnace lining refractories The early use of Mg-Cr bricks by TISCO AOD has led to the development of the use of magnesia-calcium bricks due to its high price and large environmental pollution (see the physical and chemical indicators).
The high temperature strength of Mg-Cr bricks is high, but the slag erosion resistance with thermal shock resistance and alkali resistance greater than 115 is not as good as magnesium calcium bricks. Magnesium calcium bricks have good high temperature performance and can withstand high temperatures above 1750e, and can adapt to the wide range fluctuations of alkaline slag basicity. Compared with Mg-Cr bricks, magnesium-silver bricks contain a higher proportion of CaO.CaO and SiO2 in the slag can generate a dense layer of C2S (dicalcium silicate), so that the protective brick is no longer etched. In addition, CaO has a large creep at high temperatures, which can delay the thermal shock cracking caused by temperature shock. The high temperature strength and waterproof performance of calcium bricks are not as good as those of magnesium chrome bricks. In addition, the price of magnesia-calcium bricks is lower than that of Mg-Cr bricks, and the environmental pollution is also small. Therefore, at present, TISCO has adopted magnesium-silica bricks as lining refractories of AOD. In addition, the lining thickness in the tuyere area was increased for the case where the lining etch rate was faster in the tuyere area.
Rational connection between baking system and process Because of the characteristics of refractory materials, it is not suitable for quenching and heating during use, otherwise it will cause flaking of refractory materials and greatly reduce the service life of lining. Therefore, it is necessary to formulate a reasonable AOD lining baking system, so that the new lining brick can slowly rise to high temperatures, and ensure that the lining brick is baked thoroughly, and baking of the lining is required when there is a long time waiting for steel. Avoid lining refractories because of the rapid heat in contact with molten steel, or excessive temperature drop when molten steel is left for a long time, resulting in flaking of refractories, so in the production to ensure the convergence between processes.
Smelting process adjustment In the case of certain lining refractories and steel grades, the life of AOD is a function of temperature and refining time. The final temperature of stainless steel oxidation is controlled at about 1720e, and the furnace age is inversely proportional to the refining time. Therefore, the refining time should be minimized while controlling the temperature and alkalinity. Taking 304 stainless steel smelting as an example, Taigang AOD refining time was 7580min in 2003. After several technical improvements and equipment reforms, it has now dropped to 5560min. Slag basicity and composition Adjustment of slag basicity, composition has a great influence on the lining life.
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