Methods for improving thermal shock stability of converter magnesium chromium refractory materials
Due to the intermittent operation characteristics of the converter, strict requirements are put forward for the thermal shock stability of the magnesium chromium refractory materials. Increasing the thermal shock resistance of the refractory materials can be achieved by preventing crack propagation, consuming crack propagation power, increasing material fracture surface energy and plasticity, reducing linear expansion coefficient, increasing thermal conductivity and so on.
(1) Appropriate porosity.
Surface cracks do not cause fracture immediately, but spalling and fracture caused by internal thermal stress are serious. When the porosity is appropriately increased, the cracks length of the products becomes shorter and the number increases under the action of thermal shock. The cracks are interlaced and the degree of mesh formation is enhanced. Therefore, the fracture energy required for the products to break is increased, which can effectively improve the thermal shock stability of the products. The optimum porosity of refractory products is usually controlled at 13% to 20%.
(2) Control the particle gradation of raw materials, and select raw materials with low expansion, high thermal conductivity. In order to obtain magnesia chrome refractory materials with good thermal shock resistance, it is required to increase the critical particle size and reduce the fine powder content in the chrome ore particles. The raw materials having high thermal conductivity and low linear expansion coefficient are used.
(3) Increase micro-fine cracks and form a network structure. Using the inconsistent refractory products particles and matrix linear expansion coefficient inconsistent characteristics and phase change volume effect, resulting in fine cracks in the products, has a significant effect on resisting product catastrophic damage, such as thermal spalling or fracture.
Experiments have shown that the thermal shock stability of magnesia chromium refractories can be significantly improved by increasing the Al203 content in the refractory materials or adding an appropriate amount of ZrO2 to the magnesia-chromium refractory materials. Compared with the sample incision, the sample with ZrO2 has a large number of fine cracks inside. It is because of the existence of these fine cracks that the energy of crack propagation is absorbed, which enhances the thermal shock stability of the samples, but the amount of ZrO2 added should not exceed 5%.
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