1. Thermomechanical erosion
The first thing that occurs when the slide gate plate is in use is thermomechanical corrosion. The temperature of the slide gate plate before use is very low. During pouring, the inner hole of the slide gate plate suddenly comes into contact with high-temperature molten steel (1600C) and suffers strong thermal shock (the temperature change is about 1400C). ), So a tensile stress exceeding the strength of the sliding plate is generated outside the casting hole, resulting in the formation of radial micro-cracks centered on the casting hole. The appearance of cracks is conducive to the diffusion, accumulation and penetration of foreign impurities, and accelerates the chemical attack. At the same time, the chemical corrosion reaction promotes the formation and expansion of cracks, and this cycle makes the slide hole gradually expand and damage. In addition, the scouring of high-temperature molten steel will damage the refractory material at the friction part of the steel, and cause peeling and block loss.
2. Thermochemical erosion
Thermal chemical erosion is another major cause of slide gate plate damage. Refractories for slide gate plates come into contact with high-temperature molten steel and slag during use, and a series of chemical reactions occur, causing chemical corrosion. According to the different chemical damage mechanisms of different steel grades to the sliding plate, the steel grades currently produced by Baosteel can be divided into three categories, namely, killed steel, high-oxygen high-manganese steel, and calcium-treated steel. Then according to different conditions of use, choose the corresponding material of the slide gate plate, which can increase the service life of the slide gate plate and reduce the cost of refractory materials.
The chemical mechanism of Al2O3-C and ZrO2-AI2O3-C mass slide damage:
(1) Oxidation of carbon. There are two main ways for the oxidation of graphite and carbon:-It is the oxygen in the molten steel, especially the high-oxygen steel, that oxidizes the carbon to form pores, and then the iron penetrates into the pores and makes the surface of the sliding plate adhere to the molten steel: the second is the oxygen in the air to oxidize the carbon. After the low-melting material is formed, the low-melting material continues to corrode and penetrate along the pores.
(2) Decomposition of mullite. After use, the mullite decomposes to varying degrees, transforming into columnar and crystalline corundum crystals, forming a porous structure, destroying the original dense eutectic structure composed of mullite and clinoperite, making the structure Porosity, deterioration of the structure, greatly reduced strength and corrosion resistance, accelerated the damage of the slide gate plate.