.al / Si Composite Of Al <sub> 2 </ Sub> The O <sub> 3 </ Sub>-c Materials, High Temperature Properties, Microstructure And Developed

Al₂O₃-C material possesses relatively well high temperature properties and is universal used in continuous casting for the steel making. To improve the hot strength of Al₂O₃-C material as well as to meet with the clean steel technology, high temperature properties, such as, changes in phase composition during heating process, the relationship between microstructure and properties, MOR and stress-strain behavior at different temperature, thermal shock resistance, oxidation resistance and changes in microstructural characteristics of Al/Si metal bonded Al₂O₃-C material have been investigated. On the basis, low firing temperature and low carbon content Al/Si metal bonded Al₂O₃-C slide plates have been developed and successfully used in large and medium size ladles giving satisfactory performance.The effects of Al content on phase composition, properties and microstructure of Al metal bonded Al₂O₃-C material during heating in carbon embedded condition have been studied. The results show: at low temperature range (600-800℃), Al melting which fills in the pores and contributes to sintering, densification and increase in cold and hot strength; at medium temperature range (800-1200℃), Al reacts with C and N₂ to form much Al₄C₃ and minor AlN which fills in the corundum skeleton structure leading to further densification and strength increasing noticeably of the material; at high temperature range (1200-1400℃), Al disappear, some Al₄C₃ reacts with N₂ to form AlN, Al₄C₃ and AlN form the nonoxide bonded corundum skeleton structure and take strengthening effect, the strength of the material is further increased; at high temperature range (1400-1600℃), the crystals of Al₄C₃ and AlN increase and some Al_xCO_yN_z is formed, the high cold and hot MOR of the material is retained.MOR and stress-strain behavior of Al/Si metal bonded Al₂O₃-C material at different temperatures have been studied. The results show: at low temperature range, the strength decreases with temperature increase; at medium temperature range, the strength increases noticeably with temperature rise; at high temperature range, the strength continuously increases with a slow rate. The relationship between stress and strain is characterized: the material exhibits plasticity stage at low temperature; up to 1400℃, the plastic state is remained and no viscous flow stage is observed.The effects on high temperature properties of the material with Al and Si powder addition in Al₂O₃-C material have been studied. The results show: when Al addition increases from 5% to 11%, HMOR of the material increases, thermal shock resistance and oxidation resistance are also improved; When 8% Al and 1.5～3% Si powder is incorporated into Al₂O₃-C material, HMOR of the material further increases, thermal shock resistance retains at the high level and oxidation resistance is improved noticeably.The relationship between properties and microstructure of Al/Si metal bonded Al₂O₃-C material has been studied. The results show: the bonded phase of the material is carbon at room temperature; the metal bonded phase is dominant at low temperature; at medium temperature, Al and Si react with C and N₂ in-situ forming nonoxides, the bonded phase converts gradually from metal to nonoxide; the bonded phase is nonoxide at high temperature, which takes toughening and strengthening effect leading to increase in thermo-mechanical properties of the materials. The morphology change of Al particles in Al₂O₃-C material at low temperature has been studied by using fractal theory. The results show: Al particles in the material possess fractal characteristics and the extent of metal bonded can be quantificationally described by fractal index.On the basis of the above research results, Al/Si metal bonded Al₂O₃-C slide plate material has been developed by low temperature sintering process. This new type slide plate is characterized by low carbon content, exhibit higher hot strength, better thermal shock resistance and better oxidation resistance than conventional Al₂O₃-C and Al₂O₃-ZrO₂-C plates which are fired at much higher temperature. They have been successfully used in large and medium size ladles, giving service performance of consecutive heats better than conventional Al₂O₃-C plates and about the same as Al₂O₃-ZrO₂-C plates, the bore diameter enlargement of the used slide plates is uniform and galling and cracks on the plate surface are less.The failure mechanism of the Al/Si metal bonded Al₂O₃-C slide plate in practical use is analyzed. The results show: it is the oxidation but not corrosion is the main reason cause the material damage. The process of wear may be that the nonoxides in the working section of the plate are oxidized first leading to weakening of structure and lowering of strength which would cause enlargement of bore diameter and roughening on the sliding surface. The improvement of slide plate material in the coming days should be focused on improving oxidation resistance and increasing strength of the material after oxidized. The material is simulative analyzed by finite element method, the results show: the arised thermal stress of the slide plate in practical use mainly results from the initial temperature.