Interaction of BN‐ZrO2‐SiC Ceramics with Inclusions in Si‐killed Steel

Boron nitride (BN)‐based ceramics are often used as containment refractory in thin‐strip steel production. The interaction of this material (BN‐ZrO₂‐SiC:‐MYCROSINT^® SO43) was studied using a steel‐inclusion system in a laboratory setup. Isothermal interaction tests were performed to evaluate the interaction of inclusions with this refractory. It was determined that corrosion of the BN refractory occurs through a dissolution mechanism and it was more severe in contact with steel compared to slag. A thermodynamic model was developed using FactSage to study the change in liquid steel/slag composition with refractory interaction. Thermodynamic predictions were in agreement with the experimental data obtained through isothermal interaction tests.     

Influence of calcium aluminate cement in magnesia castable on total oxygen content of interstitial free steel

Abstract

Samples of interstitial free (IF) steel buried in MgO castable bonded by calcium aluminate cement (CA) in graphite crucibles were heated at 1600°C for 90 min. Total oxygen content (TOC) of the steel was examined after heating and the refractory was investigated by SEM and EDS. It was found that TOC was higher in IF steel samples in contact with MgO castables containing 3 or 5 wt-% CA than with castables containing 7 wt-% CA or without CA. A liquid layer formed between refractory oxide and molten steel separates the refractory oxides from molten steel and inhibits direct dissolution of oxides in the molten steel. Transfer of oxygen between the refractory oxide and molten steel occurs by the formation of CaO.Fe₂O₃ at the boundary between the refractory oxide and the liquid layer, diffusion of CaO.Fe₂O₃ in the liquid phase layer, decomposition of CaO.Fe₂O₃ and dissolution of FeO into the molten steel. W ith increasing CA content in MgO based castables the CaO content in molten steel increases, but iron oxide content decreases, leading to the result mentioned above.     

不锈钢设备的连多硫酸应力腐蚀开裂机理与防护

探讨了不锈钢设备连多硫酸应力腐蚀开裂的机理,对连多硫酸的形成,及其对不锈钢设备应力腐蚀的过程,以及影响不锈钢设备的连多硫酸应力腐蚀开裂的因素进行了分析,并提出了若干种预防连多硫酸应力腐蚀开裂的措施。     

A comparative study on the slag resistance of dense corundum-spinel refractory and lightweight corundum-spinel refractory with density gradient

Lightweight corundum-spinel refractory with a density gradient structure from exterior to interior was fabricated. Slag resistance of lightweight and dense corundum-spinel refractory is investigated by X-ray diffraction, scanning electron microscopy, energy dispersive analysis, mercury intrusion porosimetry and Factsage. The results show that lightweight corundum-spinel refractory with high apparent porosity exhibits comparable slag resistance to dense corundum-spinel refractory, especially with superior slag penetration resistance. The dense exterior with small pore size in the lightweight corundum-spinel refractory can effectively hinder slag penetration. Corrosion product phases (C₂S, CA₂, CA₆, and C₂M₂A₁₄) with high melting point and inconsistent melting temperature, most of Fe and Mn elements in steel slag solubilizing in spinel, especially strip CA₆ around corundum aggregate, prevent the refractory from further slag penetration and corrosion.     

Influence Parameters on Properties of Dolomite Bricks Containing Different Bonding Systems

Pitch and tar bonded dolomite bricks are extensively used in ladles and converters for long time because of their superior properties such as. steel melt refining, easy production as well as low production cost. Recently, resin bonded dolomite bricks are presented for using in steel plants. Generally, quality and final cost of steels are affected by properties of refractories especially dolomite bricks. Therefore, recognition of influence parameters on dolomite refractory properties is very important. In this study, the effects of tar and resin as bonding systems, and addition of graphite （ 2wt% ） on the properties of dolomite refractory bricks have been investigated. Properties such as ： density and porosity, cold crushing strength, hydration time and depth of slag penetration have been studied. Results show that the bonding sys- tems and graphite have a great effect on the mentioned properties especially cold crushing strength and hydra- tion time. In addition to their low rate of pollution, resin bonded dolomite bricks show higher performance with proper technical specifications.     

Dissolution behavior of spent MgO–C refractory in the CaO–SiO2–FeO slag system as a steelmaking flux

A large amount of spent MgO–C refractory is generated in steel plant every year. Because of the similarities in chemical and mineralogical composition of slag formers and MgO–C refractory, it is possible to reuse the spent MgO–C refractory as a steelmaking flux. To achieve this goal, it should promote the dissolution of MgO–C refractory during slag forming. In this study, the effect of slag composition on the dissolution behavior of spent MgO–C refractory in the CaO–SiO₂–FeO slag system and the dissolution kinetics were investigated. It showed that the dissolution rate of MgO–C refractory was controlled by surface chemical reaction. The dissolution of MgO–C refractory led to an increase in the MgO content in slag while the FeO content decreased because the graphite in refractory was oxidized by FeO. Increasing temperature significantly promoted the dissolution of MgO–C refractory. The MgO–C refractory was readily dissolved in the low-basicity slag. A higher FeO content in slag was beneficial for the oxidation of graphite in refractory, resulting in better dissolution. The dissolution thickness of MgO–C refractory could exceed 4.0 mm under these conditions and its dissolution supplied some MgO to slag.     

Post-mortem analysis of alumina-magnesia-carbon refractory bricks used in steelmaking ladles

Post-mortem studies in secondary steelmaking ladles are an important way to determine the factors related to Alumina-Magnesia-Carbon (AMC) refractory corrosion. AMC refractory bricks installed in the impact zone of a steelmaking ladle bottom were analyzed after 100 castings. X-ray diffraction, X-ray fluorescence chemical analysis, reflected optical light microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, density and porosity measurements, and mercury porosimetry were used to analyze the chemical and physical characteristics of the slag, the unused refractory and the slag+steel attacked bricks. The corrosion process produced a specific microstructure characterized by: i) a thick discontinuous slag layer composed by secondary spinel+steel+liquid; ii) a thick dense, cracked, and continuous layer consisting of calcium aluminates+steel+liquid at the slag/refractory interface; iii) next to this layer, a wide densified layer with a uniform microstructure in which corundum aggregates and spinel crystals were linked together by elongated CaAl₁₂O₁₉ crystals.The formation of these reaction layers constituted a barrier that effectively suppressed the massive slag penetration and surely reduced the wear rate. Thermodynamic calculations based on simplified and complex condensed phase equilibrium diagrams, were used to further understanding of the corrosion mechanism.     

Study of the Corrosion of High Alumina Refractories by Al2O3-CaO Slag as a Reactive Impregnation Mechanism

The corrosion of refractories results from reactive transport,namely,transport of agents and chemical reactions of these agents with impregnated medium. On one hand,the transport involves either diffusion or impregnation depending on the state of the corrosive agents and the microstructure of the host media. On the other hand,chemical reactions may be very numerous and complex.This study focused on the reactive impregnation of Al2O3- CaO slag into porous high alumina refractory. The transport properties of the refractory material were identified by means of a dedicated capillary rising test. Chemical reactions between the solid high alumina skeleton and Al2O3- CaO slag involve successive dissolution / precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamic properties of the binary system,the kinetics of these solid / liquid reactions is not well known.Corrosion tests associated with the quenching method,XRD analyses were performed for a better understanding of the kinetics. The results of this study open up a coupling approach for predicting the corrosion wear of refractory.     

Oxidation kinetics of MgO–C in air with varying ash content

Abstract

MgO–C refractories are extensively used in metallurgical vessels in the steel industry. The graphite plays a vital role owing to its non-wettability with slag. Though quality is very important for graphite, little published data is available on the effect of varying ash content on oxidation. Since MgO–C bricks manufactured from graphite with different ash contents are regularly used for lining converters and steel ladles at SAIL plants, a study has been conducted to select an optimum graphite with low cost. Graphites with 2·8, 4·4, 12 and 20% ash content were used to make MgO–C samples in the laboratory, and oxidation properties were evaluated using an electrically heated tube furnace. Kinetic analysis shows that a chemical reaction mechanism operates in the earlier part of oxidation, followed by a diffusion mechanism in the latter part. MgO–C manufactured from graphite with 4·4% ash content was observed to have the best oxidation resistance, with an activation energy of 43·4 kJ mol^?1 during the earlier stage followed by 34·2 kJ mol^?1 in the latter.     

Corrosion mechanism of lightweight microporous alumina-based refractory by molten steel

Lightweight refractory linings for industrial furnaces have become important subjects of development in high-temperature industries. The reaction mechanism between a lightweight microporous alumina-based refractory material and molten steel was investigated in this study. The main mechanism of refractory damage was structural spalling, caused by steel penetrating the pores. The many micropores in lightweight microporous alumina have high specific surface area and reactivity, inducing the formation of FeO–Fe₂O₃–Al₂O₃ phases. This impeded the further penetration of molten steel and the direct dissolution of refractory oxides, promoting greater resistance to molten steel than that shown by common tabular alumina-based refractories, in which Fe does not react and steel penetration through the pores cannot be retarded.     

Kinetics of Corrosion of BN–ZrO2–SiC Ceramics in Contact with Si‐Killed Steel

The mechanism and kinetics of corrosion of BN–ZrO₂–SiC (MYCROSINT^®SO43) by molten Si‐killed steel was studied. Isothermal corrosion tests were performed for duration between 2 and 8 h. Refractory and steel composition and morphology changes were investigated. A kinetic model using process simulation software METSIM and thermochemical software FactSage was developed to understand refractory–steel interactions. The corrosion process showed a deviation from parabolic kinetics and was fitted by a combination of linear and parabolic terms. It was determined that corrosion of the BN–ZrO₂–SiC refractory was governed by dissolution of SiC and BN and removal of ZrO₂ as the other phases were eliminated.     

Performance of a ceramic frit anti-oxidation coating on a MgO-C refractory brick

In steel production, ladles must be preheated to minimize the heat loss of the steel melt, prevent thermal shock of refractory bricks (MgO-C), and to maximize the lining life of ladle. Partial oxidation of MgO-C bricks begins in the graphite bond during the preheating. Oxidation of graphite bond also causes a decrease in performance of the bricks because of an increase in the brick porosity. In this article, coating on a MgO-C brick surface by a ceramic film to protect against carbon oxidation was studied. Coated and un-coated bricks were heated at 1200 °C, cooled to room temperature, then the brick properties investigated. The oxidization resistance properties of brick with coating were much better than those without coating, which should lead to longer refractory service life.     

水性超薄型防火涂料的制备及其性能

以有机硅改性丙烯酸树脂为基础树脂,聚磷酸铵、季戊四醇、三聚氰胺为化学阻燃剂,可膨胀石墨为物理阻燃剂,制备了结构钢用水性超薄型防火涂料。采用高温加热、垂直燃烧法、扫描电子显微镜、热重分析、X射线衍射等研究了基础树脂与不同阻燃剂的配比对涂料防火性能的影响。结果表明:基础树脂、化学阻燃剂与物理阻燃剂的质量比为7∶11∶2时,所配制涂料的膨胀倍率达17.78倍,耐火时间为52 min且生成了高质量的炭层。该涂料刷涂方便,可明显提高结构钢到达屈服极限的时间,增加高温使用寿命。     

Reaction mechanism between MgO crucible and AerMet100 steel during vacuum induction melting

AerMet100 steel has strict composition and inclusion requirements. Therefore, its reaction with MgO refractory during vacuum induction melting cannot be ignored. In this study, the reaction mechanism between the MgO refractory and AerMet100 steel during the refining stage was investigated using a MgO crucible. The influence of the MgO crucible on AerMet100 steel composition and inclusions under refining vacuum pressures of 50–100 and 5–10 Pa was compared. The results indicate that SiO₂, Al₂O₃, and MgO in the crucible decompose and are reduced by C in the liquid steel, which results in the increase of Si, dissolved Al (Als), and dissolved Mg (Mgs) content in the liquid steel. The increase of Ca content is due to the reduction of CaO in the crucible by C in the liquid steel. The reaction of Al₂O₃ inclusions and Mgs in the liquid steel is the primary generation method of MgO·Al₂O₃ spinel inclusions. As the Mgs content in the liquid steel increases, Al₂O₃ inclusions transform into MgO·Al₂O₃ spinel inclusions along the path Al₂O₃ + Mgs → Al₂O₃ with a small amount of MgO + Mgs → MgO·Al₂O₃ spinel. In contrast, the vacuum pressure of 50–100 Pa is more effective at controlling the composition and inclusions of AerMet100 steel and is a more appropriate choice for the refining vacuum pressure.     

钢基体表面熔覆层的耐蚀性

用热等离子弧在Q 235钢基体表面熔覆材料为Stellite N i60商用镍基自熔性合金粉的涂层,涂层厚1 mm。对熔覆层的耐蚀性能进行了研究,并对耐蚀机理进行分析,结果发现,熔覆层耐碱的腐蚀性最好,其次是耐食盐水腐蚀,耐盐酸的腐蚀性相对较差。     

Insights into ZrO2- and Al2O3-based submerged entry nozzle clogging for the continuous casting of RE-treating sulfur resistant casing steel

The ZrO₂- and Al₂O₃-based submerged entry nozzle (SEN) clogging during continuous casting of a RE-treating sulfur resistant casing steel is studied experimentally based on morphological analysis and the related thermodynamic calculations. The results show that the ceramic cloggings exists both in the inner-wall and outlet regions of SEN, while the latter is the main reason for terminating the casting with its clogging reaching 77% in the nozzle cross section area. The clogging is caused by RE-containing inclusions from molten steel and reoxidation products by the reaction between RE in molten steel and the initial formed cloggings on nozzle refractory. The possible existence state of RE in molten steel with its content has been discussed, and the clogging mechanism studied in detail. To prevent nozzle clogging, suggestions are given for continuous casting of the RE-treating steel with a modified RE treatment strategy for less solid inclusions and solute [RE] presented in liquid steel during refining process. Additionally, the optimization of nozzle geometry and its refractory materials may help as well.     

Effect of different metal powder anti-oxidants on N220 nano carbon containing low carbon MgO-C refractory: An in-depth investigation

Effect of three different metal powder antioxidants, namely, Al, Si, and Mg was studied on the development of N220 nano carbon containing low carbon MgO-C refractory. The study was also extended to conventional MgO-C refractory compositions with 16% graphite content. All the refractory compositions were processed as per conventional MgO-C refractory manufacturing techniques and were evaluated for physical, mechanical, thermo-mechanical properties, oxidation resistance and static corrosion resistance against steel converter slag. Microstructural developments and in-situ ceramic phase formation in the compositions were also studied. The results show that nano carbon containing low carbon MgO-C refractory compositions have better properties than conventional composition and among the three anti-oxidants, the aluminum metal powder has shown the improved properties.     

Use of aluminum phosphate as a bond for refractory corundum products and washes

Summary The use of aluminum phosphate is desirable for preparing corundum products and washes based on commercial calcined alumina.A composition was developed ensuring strong bonding of corundum refractories and also of corundum refractories with steel and graphite.The bonded refractory components (corundum) are tightly held on graphite components of thermocouples after 15 h operation in the walls of electric arc furnaces at 2000°C.Aluminophosphate bond increases the spalling resistance of corundum products and also raises their strength.     

稀土对金属表面钝化作用研究进展

总结了碳钢和不锈钢以及铝、锌、铜、镁等金属及其合金稀土钝化处理的国内外研究状况。阐述了稀土钝化膜的防蚀机理。指出了稀土钝化工艺在取代铬酸盐钝化中的优势及其应用前景。     

钢水的钙处理及含尖晶石耐火材料的开发利用

钙处理铜水中［Ｃａ］在钢水、耐火材料界面上与材料中的ＳｉＯ２进行化学反应，生成的ＣａＯ又被吸附在耐火材料表面上。因材料材质不同，表面所形成的矿物不同及液相比的差异，导致抗侵蚀能力的不同。含尖晶石耐火材料则可以提高这种抗侵蚀能力。利用对ＭｇＯＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２四元系研究结果，指出尖晶石耐火材料的性能除了与Ａｌ２Ｏ３、ＭｇＯ、尖晶石含量有关外，还与其它矿物组成有密切关系，并指出最佳的矿物组成范围。