Improvement Of Medium-high Temperature Performance And Damage Mechanism Of Al₂O₃-C Unfired Slide Gates

With the continuous improvement of the role and position of slide gates in steelmaking process,the processing and manufacturing technology of slide gates is also being improved.In order to reduce production cost,energy consumption and environmental pollution,slide gates without high-temperature firing,tar immersion and low-temperature treatment is the development direction.The Al₂O₃-C unfired slide gates as refractory components with function of flow controlling for continuous casting have been widely used,due to their significant advantages such as low energy consumption,low cost,short production cycle and environment-friendly.But unfired slide gates still exist a series of problems including hole expanding,easy peeling,cracking and so on.At present,there are many researches on the high-temperature performance of Al₂O₃-C unfired slide gates,but few studies on the medium temperature performance of the Al₂O₃-C unfired slide gates.In this paper,the apparent porosity,bulk density,oxide layer thickness,compressive strength and thermal shock resistance of Al₂O₃-C unfired slide gates specimens with the addition of Zn powder,Mg-Al alloy powder and microsilica were studied after heat treatment at 600?,800?and 1000?for 3 h.The optimum formula was selected to make Al₂O₃-C unfired slide gates.Field experiments were carried out in Shandong Laiwu Iron and Steel Co.,Ltd.to analyze the damage of the residual bricks after pouring steel once.The results show that the medium and high temperature properties of the slider can be improved by introducing proper amount of Zn powder into the Al₂O₃-C unfired slide gates.The addition of Zn powder changed the reaction process of Al powder and strengthened the metal bonding of the Al₂O₃-C unfired slide gates.The mid-temperature performance defects of Al₂O₃-C unfired slide gates was improved.The apparent porosity of slide plate samples at 600?,800?and 1000?was reduced,the cold crushing strength was improved,the thermal shock resistance was improved and antioxidant activity has also been improved.However,excessive addition of Zn reduced its performance,and the amount of Zn powder should not exceed 1.5%.When Mg-Al alloy powder replaces part of Al powder with the increase of Mg-Al alloy powder,the compressive strength of the sample increases after heat treatment at 600?.The addition of Mg-Al alloy powder can improve the low-temperature properties of Al₂O₃-C unfired slide gates.However,when the heat treatment temperature rises to 800?and 1000?,the apparent porosity increases and the bulk density decreases,the surface oxidation of the sample is obvious,and the performance of the slider decreases obviously.After the addition of microsilica in the Al₂O₃-C unfired slide gates,the apparent porosity decreases and the bulk density increases.Under the oxidation atmosphere,because microsilica can prevent oxygen from entering,the oxide layer thickness of unfired slide gates with microsilica decreases.Microscopic analysis of the Al₂O₃-C unfired slide gate brick with the addition of Zn powder after pouring steel once shows that the damage of the working belt around the casting hole is more serious.There are only a small amount of steel slag and scratches appear on the slide surface due to the mechanical damage and chemical erosion of the flowing molten steel and slag.