Al/Si复合Al₂O₃-C材料的高温性能、显微结构及研制

【作者】 石凯；

【导师】 钟香崇；

【作者基本信息】 郑州大学 ， 材料学， 2007， 博士

【摘要】 由于铝碳材料具有相对较好的高温性能，而广泛应用于连铸功能性耐火材料中，为进一步提高其高温性能，满足洁净钢技术的发展要求，本论文研究了Al／Si复合Al₂O₃-C材料的高温性能及显微结构，包括加热过程物相组成、结构及性能的变化，不同温度的抗折强度和应力—应变关系，Al／Si加入量对高温强度、抗热震性能和抗氧化性能的影响以及显微结构特征的变化。在此基础上，研制了低温烧成、低碳Al／Si结合Al₂O₃-C滑板制品，在大中型钢包上取得了较好的使用效果。研究了在埋碳加热过程中Al复合Al₂O₃-C材料组成、性能及结构的变化。结果表明：600～800℃的低温阶段，Al熔化，填充空隙，使材料致密，常温和高温强度提高；800～1200℃的中温阶段，随着温度升高Al与C反应生成大量的Al₄C₃，少量的Al与N₂反应生成AlN，Al₄C₃和AlN填充在刚玉骨架结构中，使材料进一步致密，常温和高温抗折强度显著增加。1200～1400℃的高温阶段，Al消失，部分Al₄C₃与N₂反应转化为AlN，AlN和Al₄C₃形成非氧化物结合的结构，起强化作用，使材料的强度进一步提高；1400～1600℃的高温阶段，AlN和Al₄C₃晶体发育长大，使材料保持较高的常温和高温强度，并观察到少量的Al_xCO_yN_z。研究了Al／Si复合Al₂O₃-C材料在不同温度下的抗折强度和应力—应变关系，结果表明：低温阶段随着温度升高材料的强度降低，中温阶段其强度显著增加，高温阶段材料的强度继续增加，但增加的幅度减小。材料应力—应变关系特征为：低温时即呈现塑性状态，一直到1400℃仍处于塑性变形范围，未观察到粘滞流动现象。研究了Al／Si加入量对材料高温性能的影响。结果表明：Al从5％增加到11％，材料的高温抗折强度提高，抗热震性能和抗氧化性能得到改善。在8％Al的基础上加入1.5～3％Si，材料的高温抗折强度进一步提高，抗热震性能保持较高水平，抗氧化性能明显改善。研究了材料的显微结构与性能的关系。结果表明：常温时材料的结合方式是碳结合，低温阶段以金属结合为主，中温阶段Al／Si与C、N₂原位反应生成非氧化物，材料由金属结合逐渐向非氧化物结合转变，高温时形成非氧化物结合，起到增强增韧作用，使材料具有较好的高温机械性能。用分形理论研究了材料中金属铝颗粒低温阶段的形貌变化，结果表明：金属铝颗粒的形貌具有分形特征，可用分形维数来定量描述Al₂O₃-C材料金属结合方式的程度。根据上述研究结果，采用低温烧成工艺，研制了Al／Si结合Al₂O₃-C滑板制品。该滑板与高温烧成的Al₂O₃-C和Al₂O₃-ZrO₂-C质滑板相比，碳含量低，高温强度高，具有较好的抗热震性和抗氧化性。经大中型钢包的批量使用表明，其连续使用次数高于烧成的Al₂O₃-C滑板，与Al₂O₃-ZrO₂-C滑板相当。用后滑板的扩孔均匀，拉毛较少，裂纹微细。对Al／Si结合Al₂O₃-C滑板用后的残砖进行了分析研究，结果表明，滑板在使用时的损毁过程是：表面工作层中的非氧化物首先被氧化，导致结构疏松，强度降低，在铸孔处由于高温钢水冲刷引起铸孔扩大，在滑动面处因机械摩擦造成滑动面拉毛。因此该滑板材料今后改进的重点应是提高其抗氧化性及氧化后的强度。用有限元进行了模拟分析，结果表明：滑板在使用过程中产生的热应力主要决定于其初始温度，根据应力分布情况可以优化滑板结构。更多还原

【Abstract】 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.更多还原