Effect of Microsilica Addition on Properties of CMA72 Bonded Al_2O_3-MgO Castables

CMA72 bonded Al_2O_3-MgO castable is promising for application of steel ladle wall,because of unique combination of thermo-mechanical properties,slag corrosion resistance and cost benefit. In these castables,microsilica can be introduced to counterbalance the expansion generated by spinel formation. In this paper,the effect of microsilica dosage on properties of castables was evaluated. Expansion,expressed by the permanent linear change( PLC),is highly dependent on the dosage of microsilica. Unexpected expansion occurs when the dosage of microsilica is too low due to dominant effect of spinel and CA_6 formation. Too high dosage results in sintering shrinkage,which is related to amount of liquid phase generated by microsilica addition. In addition,HMOR declines dramatically with increasing microsilica dosage. Considering the balance between expansion control and hot property retention,1. 0 mass% of microsilica is recommended for the castable containing 4 mass%of magnesia.     

Alumina-spinel castable for steel ladles: An overview

Alumina-spinel castable has excellent refractory properties, including high volume and thermal stability, good hot strength, and excellent resistance against corrosion, erosion, and thermal spalling. Excellent refractory properties have made it a preferred lining for steel ladles, reducing the erosion and corrosion of molten metal and slag and improving the ladle life and efficiency for decades. These castables are also significant for the replacement of chrome-bearing refractories that cause several health hazards. The current review paper covers preformed and in situ spinel containing alumina castables. It focuses on the importance of these castables in the sidewall and bottom portion of the steel ladle in detail, the effect of spinel and MgO content, and the factors affecting castable properties. The review also covers the final properties of castable and the application areas of alumina-spinel castable in steel ladle, purging plugs, and RH-degasser.     

博耐特(Bonite)--一种新型的合成致密CA6耐火原料

介绍了基于六铝酸钙(CA_6)矿物相的一种新型合成致密耐火骨料——博耐特(Bonite);讨论了博耐特原料以及由博耐特、板状刚玉或者二者复合制备的多种试验用浇注料的理化性能;并结合博耐特的相关应用领域进行了博耐特耐火材料抗铝液侵蚀、热机械性能、热导率和微气孔等较为前瞻性的试验和探索。     

钢包粘渣与包衬耐火材料

阐明了钢包粘渣与包衬耐火材料存在一定的关系 ,抗渣渗透性差、容易出现开裂的包衬耐火材料容易粘渣。为防止钢包粘渣 ,适于采用抗侵蚀性和抗渣渗透性优良的尖晶石砖、铝尖晶石 (或铝镁 )浇注料、低密度浇注料以及抗剥落性好的刚玉 -锆英石浇注料作包衬耐火材料     

Steel ladle well block post mortem analysis

Spinel-containing castables are widely used as steel ladle refractory lining, due to their outstanding basic slag (calcium aluminate based) corrosion resistance. In order to understand their corrosion mechanism, a post mortem evaluation of a steel ladle well-block castable was carried out. The interaction among the refractory castable, slag and molten steel was mainly evaluated by light optical and scanning electron microscopy using SEM multielement mapping. The results indicated that an equilibrium state was attained, leading to the formation of a densified barrier that protected the original castable from corrosion located at the deepest regions, regarding the metal flow. Each one of these layers was evaluated, underscoring the damage that the refractory is liable to during application and also the possibilities of steel contamination, due to castable wear, and reoxidation. The experimental results were compatible with the literature, pointing out how corrosion takes place and the possibilities to reduce its negative effect.     

Comparative Study of Lightweight Corundum with Different Microstructures and Its Effect on Slag Resistance of Al_2O_3-MgO Castables

Corundum-spinel castables containing lightweight aggregates have drawn many attentions due to their potential for energy-saving,especially when applied in the high-temperature region,such as the work lining of refining ladle. One main aspect that restricts their application is the slag corrosion performance. In this study,one dense tabular corundum and three kinds of lightweight corundum were chosen as aggregates to prepare four different corundum-spinel castables. The slag resistance was compared through the induction furnace corrosion test. SEM-EDS,XRD,and thermodynamic and kinetics analysis were adopted for the discussion of the corrosion mechanism. Results show that the crystal grain size and shape of aggregates are important for the slag corrosion resistance of lightweight corundum-spinel castables under dynamic condition( enforced convection),yet the effects of pore characteristics are not dominated. Aggregates with large flake-like crystal grains show a thicker dissolution diffusion boundary layer and a lower dissolution rate,resulting in a favorable corrosion resistance of the castable. The poor microstructure of the aggregates,namely,larger pores and small and spherical grains,would cause deterioration of castables ' slag resistance.     

CaO含量对刚玉质浇注料性能与显微结构的影响

通过控制铝酸钙水泥加入量,研究了CaO含量分别为0、0.5%、1.3%、1.7%、2.5%、3%、3.5%、4.9%、5.6%和7.5%时对刚玉质浇注料烧结性能、抗热震性和显微结构的影响,同时借助XRD、SEM、EDS和高温热膨胀仪等手段对浇注料的物相变化、热膨胀系数和显微结构进行了分析和观察。结果表明:刚玉质浇注料中CaO含量显著影响着浇注料的烧结性能、抗热震性及其显微结构,当CaO含量低于2.5%时,随着CaO含量的增加,浇注料中片状CA6逐渐增多,并伴随着大量的体积膨胀,导致浇注料体积密度下降,显气孔率上升;当CaO含量超过2.5%时,随着CaO含量增加,浇注料中CA2相含量增加,CA6相含量逐渐减少,浇注料体积密度开始增加,显气孔率下降,线膨胀率减小,CaO含量高于5.6%的浇注料出现了收缩;刚玉质浇注料的抗热震性与显微结构密切相关,CaO含量为4.9%～7.5%的刚玉质浇注料具有很好的抗热震性,这是由于浇注料基质中粒状CA2与片状CA6相互穿插,刚玉骨料边缘片状CA6向基质中生长,强化了基质与骨料的结合,同时CA2相具有低膨胀性,导致浇注料具有较高的强度保持率和抗热震性。     

Spinel Castables for Steel Ladle Lining:In-Situ Versus Preformed

The paper discusses the difference in the formulation concepts of alumina-spinel (spinel containing) and alumina-magnesia (spinel forming) castables and the influence on their physical properties. The individual property profile is discussed with respect to the requirements of refractory lining materials for the different zones of a steel ladle.     

The corrosion resistance of microsilica-containing Al2O3–MgO and Al2O3–spinel castables

Microsilica addition in Al₂O₃–MgO and Al₂O₃–spinel castables helps to improve their flowability and partially accommodate their residual expansion after firing. Nevertheless, there is a lack of conclusive statements in the literature regarding the effects of microsilica on one of the main requisites for steel ladle refractories: corrosion resistance. In the present work, the performance of alumina–magnesia and alumina–spinel with or without microsilica when in contact with a steel ladle slag was evaluated based on three aspects: the material's physical properties, its chemical composition and the microstructural features before the slag attack. According to the attained results, microsilica induced liquid formation and pore growth during sintering, favoring the physical slag infiltration. Moreover, due to this liquid, CA₆ was formed in the matrix, mainly for the Al₂O₃–spinel composition, which also favored the castable dissolution into the molten slag.     

Effects of aggregate microstructure on slag resistance of lightweight Al2O3-MgO castable

Corundum-spinel castables using lightweight aggregate have drawn much attention due to their energy-saving potential, in particular when they are applied in high-temperature areas, such as the work lining of refining ladle. One of the main issues which hinder their application is their relatively poor slag corrosion performance. In this study, one type of dense tabular corundum and three types of lightweight corundum were chosen as aggregates to prepare four different model corundum-spinel castables. Their slag resistance was evaluated by an induction furnace corrosion test method. As well as SEM, EDS, and XRD characterizations, thermodynamic and kinetic analyses were carried out to assist understanding the corrosion mechanism. Results indicated that size and shape of crystalline grain in aggregate were important for the slag corrosion (dissolution) resistance of lightweight corundum-spinel castables under dynamic condition (enforced convection), whereas the effects of pore characteristics were not significant. Use of aggregates having large average crystal size and flake-shaped crystals led to a thicker diffusion boundary layer and lowered dissolution rate, i.e., good corrosion resistance, whereas use of aggregates with small and spherical crystals and larger pores led to poor slag resistance.     

Multifunctional Refractory-lined Vessel: Ladle Aggregate

A ladle primarily is a container used to transport molten steel from the steelmaking unit to the casting facility.The essential requirements are heat resistant,insulative and strong enough to hold molten steel up to 300 t,with a structure of multilayered refractory lining in a steel shell vessel.When a ladle is assembled with three-phase graphite electrodes,a ladle furnace forms,starting steel refining process with/without the vacuum tank degasser and RH circulating degasser,in order to meet the growing demand on high purity and higher quality steel.The working lining is under aggressive conditions that comprise the chemical reaction with molten steel,the severe corrosion of liquid slag,the disaggregation through oxidation,and the strong stress due to the impacting of the melts and gases and the effects of thermomechanical behaviors.Magnesiacarbon brick is one of the major materials,being indispensable for the slagline of a ladle furnace.Alumina-magnesiacarbon brick has played an important role to substantially increase the service life in the metal zone,from the early lining materials of high alumina and doloma bricks.The permanent lining must assume sufficient responsibility to allow finishing the process of the engaged charge in case of a failure in the working lining.The insulation layer must be as thin as possible in order to maximize the ladle’s capacity,and reduce the shell temperature for saving energy.In this issue,several integrant refractories are reviewed or investigated in order to compile a lining overview,and to contribute a prolonged service life under aggressive working conditions of the ladle furnace.     

不锈钢冶炼用铁水包Al2O3-SiC-C内衬砖的性能与侵蚀机理

铁水包内衬材料长期服役于间隔周期较长的高、低温交替环境,极易发生剥落与侵蚀损毁。为了探索影响铁水包内衬材料使用寿命的主要因素,对市面上四种铁水包Al₂O₃-SiC-C内衬砖的化学成分、物相组成、物理性能和微观结构进行了分析,并以高炉渣为侵蚀介质,重点研究了不锈钢冶炼用铁水包Al₂O₃-SiC-C内衬砖的侵蚀机理。结果表明:铁水包Al₂O₃-SiC-C内衬砖中Al₂O₃含量越高,高温下制品的液相量越低,越有利于提高耐火砖的高温力学性能;随着含碳量的增加,铁水包Al₂O₃-SiC-C内衬砖的抗渣性得到明显改善,但抗氧化性及高温抗折强度呈下降趋势;高炉渣中CaO、MgO向耐火砖中渗透,与耐火砖中的Al₂O₃、SiO₂发生反应形成高熔点的镁铝尖晶石及低熔点的钙长石等,生成的低熔相会加剧耐火砖的侵蚀。     

Structure and properties of lightweight magnesia refractory castables with porous matrix

To improve the energy-saving capacity of magnesia refractory castables for working lining of high-temperature kilns, this study presents the researches on microstructure and properties of lightweight magnesia refractory castables with porous matrix fabricated by direct foaming method. The results show that formation of closed-pores in the matrix significantly enhanced high-temperature thermal insulation performance of castables with minor changes of slag corrosion resistance. The thermal conductivity of the lightweight magnesia castables at 1000 °C was below 1.2 W/m·K, which is 47.8% lower than that of the referenced magnesia castable. The increasing content of SDS (foaming agent, over 0.02 wt%) led to increments of size and number of large-sized pores, resulting in the significantly decreased density and mechanical performances. The slag resistance mechanism reveals that, in addition to intergranular penetration, the accumulation of slag and penetration between adjacent pores were the major ways of slag mass transfer in lightweight magnesia castables. In conclusion, controlling the size (below 53.2 μm), number and distribution of closed-pores in the matrix is effective to realize the coupling of high thermal insulation, mechanical properties and slag resistance for lightweight magnesia castables used in the metallurgical field.     

矾土基高铝—尖晶石质钢包浇注料的研制和应用

以特级铝矾土、矾土基尖品石和烧结镁砂等为主要原料，采用超细粉凝聚结合，并对基质的化学矿物组成进行优化，开发出了矾土基高铝—尖晶石钢包浇注料。其烘烤特性良好，施工性能、物理性能及抗渣性比传统水玻璃结合的铝镁浇注料有显著提高。经在全国十多家钢厂的中小型钢包上使用，在绝大多数情况下其寿命比传统水玻璃结合的铝镁浇注料或铝镁炭发砖提高了１００％以上。     

钢包渣线用镁锆铬质无炭浇注料的研制

精炼钢包渣线使用含炭耐火材料存在着使钢水增碳的问题 ,需要研制抗渣侵蚀和渗透能力较强的无炭钢包渣线材料。以轻烧氧化镁和锆英石为原料 ,采用湿法共磨工艺 ,合成了镁锆质熟料 ,并以此合成料为主要原料 ,加入工业Cr2 O3细粉、锆英石细粉及硅微粉等研制了无炭的镁锆铬质钢包浇注料。实验证明 ,制得的镁锆铬质浇注料高温强度较高 ,高温收缩率较小 ,抗渣侵蚀和渗透能力较强。     

A low bulk density,low thermal conductivity permanent lining castable for tundish obtained by adding pearlescent sand

The precise control of molten steel temperature in tundish is a key factor to ensure the quality of the cast billets, so it is important to develop permanent lining castables for tundish with low thermal conductivity and bulk density. In this work, the hydrophobic modification of pearlescent sand was carried out with hydrogen silicone oil, and 3% of modified pearlescent sand was added to mullite-bauxite castable to realize its low thermal conductivity and light weight. It is found that modified pearlescent sand still has good hydrophobicity at 350°C, the addition of modified pearlescent sand effectively increases the apparent porosity and reduces the bulk density of the castable. At 1500°C, the bulk density of modified pearlescent sand-castable is 25.54% less than that of conventional castable. Compared with conventional castable, the mechanical properties and thermal shock resistance of modified pearlescent sand castable are worse, but they are sufficient to meet the use conditions of tundish permanent lining castable. At 600–1000°C, the thermal conductivity of the modified pearlescent sand castable is about 30% lower than that of the conventional castable, which proves that the addition of modified pearlescent sand can significantly improve the thermal insulation performance of mullite-bauxite castable.     

多孔球形莫来石基浇注料的制备及性能研究

为制备保温性能及机械性能均较优异的高温窑炉用隔热耐火材料,以多孔球形莫来石、矾土细粉、α-Al₂O₃微粉、硅微粉和Secar71水泥为主要原料,制备了多孔球形莫来石基浇注料,研究了矾土细粉掺量对多孔球形莫来石基浇注料机械性能、导热系数、抗侵蚀性能及热震稳定性的影响。结果表明,改变矾土细粉的掺量,可使多孔球形莫来石基浇注料在保持较高机械性能的基础上提高保温性、热震稳定性和抗侵蚀性能。随着矾土细粉掺量的增加,多孔球形莫来石基浇注料的机械性能变化不大,但导热系数小幅降低,抗侵蚀性能出现较大差异,热震稳定性先提高后降低。当矾土细粉掺量为28%(质量分数)时,多孔球形莫来石基浇注料的机械性能、热震稳定性及抗侵蚀性能良好,在1 000 ℃时导热系数为0.905 W·m^-1·K^-1。多孔球形莫来石基浇注料的导热系数低于中间包和钢包永久层用高铝浇注料,可替代中间包、钢包永久层用高铝浇注料以减少热损失。     

Effect of carbon black on corrosion resistance of Al2O3–SiC–C castables to SiO2–MgO slag

Metallurgical solid waste recycling is the shape of things to come in green development of Chinese iron and steel industry. Utilization of ironworks slag for producing mineral wool at high temperature is an important approach. However, refractory lining is seriously corroded by the SiO₂–MgO based slag at 1600 °C during the production process. Different production steps need different atmospheres, the changeable service atmospheres (air and reducing atmosphere) put forward high requirements for slag resistance. The Al₂O₃–SiC–C castables containing carbon black are usually used in iron runner, which faces high-temperature service condition of 1450 °C–1500 °C. Nevertheless, the function of carbon black in the Al₂O₃–SiC–C castables at 1600 °C is till essentially unknown. In the current study, the carbon black was introduced to tabular alumina based Al₂O₃–SiC–C castables to improve corrosion resistance to SiO₂–MgO based slag at 1600 °C. The result showed that 0.4 wt% carbon black was suitable for the castables, which the slag resistance of castables was significantly improved. The carbon black had contributed to block slag by wettability resistance. By comparison with the castables without carbon black, the corrosion index and penetration index had been reduced by 20.2% and 28.0%, respectively, under air atmosphere. And there were little corrosion or penetration under reducing atmosphere for castables with 0.4 wt% carbon black. For the mechanical properties, the Al₂O₃–SiC–C castables with 0.4 wt% carbon black could serve production process although the carbon black impaired the physical properties.     

CaO含量对Al2O3-MgO-CaO系浇注料性能的影响

高纯度的Al2O3-MgO-CaO系浇注料正广泛应用于精炼钢包的透气砖、座砖、工作衬及包壁修补料等,纯铝酸钙水泥既是Al2O3-MgO-CaO系统浇注料的结合剂,同时又是浇注料中CaO的主要来源.本试验通过改变纯铝酸钙水泥的加入量来改变CaO的含量,探究高温下形成的CA6等矿相对体系性能的影响.结果发现:氧化钙以本研究中的纯铝酸水泥形式引入时,随其引入量的增加,材料经110 ℃处理后的物理性能呈现优化的趋势;CA6形成产生的体积膨胀在促进结构的致密化的同时,当达到一定程度时,会导致材料结构劣化,因此材料经1550 ℃处理及5次热循环后,其物理性能呈现先提高后降低的趋势.综合各项性能认为,纯铝酸钙水泥加入量在5wt%~8wt%时其高温强度及抗热震性能较为优异.