镁硅质防粘渣涂料的防粘渣试验及其应用

为了验证以菱镁矿、石英、黏土、氧化铬微粉及磷酸盐为原料制成的镁硅质防粘渣涂料的防粘渣性能,采用静态坩埚法(1 600℃3 h,空气气氛)对比研究了转炉钢包渣线用普通镁碳砖和VOD钢包渣线用低碳镁碳砖在涂覆该涂料前后的防粘渣性能,分析了试验后涂料的显微结构,探讨了涂料的防粘渣机制,并在宝钢进行了实际使用试验。结果表明:防粘渣涂料在熔渣与镁碳砖之间形成了明显的隔离层,起到了较好的防粘渣作用。这是由于,防粘渣涂料在1 600℃的平衡物相为MgO、M2S及MA与MK的固溶体,无液相出现,隔离了镁碳砖与熔渣的接触,不易被钢渣溶解,也不与镁碳砖发生烧结反应,还在一定程度上保护炭素不被氧化,加之其较大的体积收缩和排气反应,使其容易与粘附在其表面的熔渣一起脱落,从而起到防粘渣的作用。实际使用表明,该涂料大大减轻了钢包的粘渣程度,并延长了渣线和包口镁碳砖的使用寿命,得到了钢厂的认可。     

Evaluation of oxidation resistance of MgO-C bricks in oxy-combustion and air-combustion

There are important advantages in oxy-fuel technology over conventional combustion, such as the reduction in fuel consumption and gaseous emissions. However, before its use in the steel industry, it is essential to know that the alteration of the firing system can lead to an increase in the wear of the oxide-carbon refractories. In the present work, four types of MgO-C bricks were fired under oxy-fuel and air-fuel conditions in a semi-industrial furnace, simulating the heating of a steelmaking ladle. The fired bricks were evaluated in terms of weight loss, thickness of the decarburized layer, and phases and microstructure formed in this layer. The results indicated few differences in the properties of the bricks fired in the two systems. The brick with 12% carbon and Al antioxidant showed the highest oxidation resistance among all bricks investigated. The most important factor for the use of the oxy-fuel system was the correct selection of the refractory microstructural properties, including the utilization of antioxidant additives.     

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.     

The Effect of Graphite Particle Size on Properties of Low Carbon MgO-C Composite Materials

The effects of graphite granularity on the properties of low carbon MgO-C based materials have been investigated in the work. Large crystal fused magnesia, natural flake graphite with different particle sizes and anti-oxidant were adopted as raw material for preparation of specimens. However, the results show that the physical properties oxidation resistance and thermal shock resistance of low carbon MgO-C materials with content of 4.0 wt% graphite are improved obviously through the use of special and suitable size graphite. The excellent performance achieved was considered as a result of microstructure modification of MgO-C materials. Therefore, it is suggested that both fine and micro grade natural flake graphite used for production of low carbon MgO-C bricks.     

Properties of MgO–Fe–C refractories as linings of vanadium-extraction converter

For the purpose to extend the service life of MgO–C bricks used as linings of vanadium-extraction converters, MgO–Fe–C bricks with different carbon content were designed and the properties of this novel refractory were investigated by comparing to the traditional MgO–C bricks. The results showed that the poor service life of MgO–C bricks was due to the poor sinterability of the oxidized layer at 1400 °C, whereas the oxidized layer of MgO–Fe–C brick was well sintered due to the oxidation of Fe particles in the oxidized layer and formation of MgO–FeO_ss in air atmosphere. Excellent oxidation resistance and corrosion resistance against vanadium containing slag were also obtained due to the increase of compactness of oxidized layer and concentration of FeO in the oxidized layer compared to MgO–C bricks, and it is considered that MgO–Fe–C brick is a favorable substitute of MgO–C refractory to be used as linings of vanadium-extraction converters.     

再生镁碳砖和铝镁碳砖在精炼钢包上的应用

介绍了采用64%～88%质量分数的用后钢包再生料制造的再生镁碳砖和再生铝镁碳砖的性能以及在精炼钢包上的应用情况。使用结果表明,根据使用条件和再生料的特点,把镁碳砖的制造技术和使用条件结合起来设计制造的再生镁碳砖,其使用效果显著好于原镁碳砖:在300 t精炼钢包渣线上的使用寿命提高15%,在50 t LF-VD炉渣线上的使用寿命提高50%以上。     

Method of raw materials selection for production of the MgO-C bricks of comparable properties using PCA and K-medoids

MgO-C refractories are zonally installed in most of the key heat devices of steel and iron metallurgy with the exposure to various corrosive factors. One of the most significant factors is low-temperature decarburization resulting in the oxidation of carbon in MgO-C refractories and loss of its properties. Moreover MgO-C materials are exposed for direct attack of liquid slag or steel melt which easily infiltrate the porous, decarburized hot face of the bricks. Cost of MgO-C materials of high quality is important for refractories user. For this reason researches try to develop materials of high quality but with lower cost by substituting fused raw materials with sintered ones or with recycled MgO-C. In this article, method of selecting the raw materials for production of MgO-C bricks with comparable properties is shown. Twenty different variants of MgO-C materials were prepared with the use of various quality raw materials. Basic properties of the industrially produced MgO-C bricks were measured. To select recipes with similar quality principal components analysis method and K-medoids algorithm were applied. To verify the results corrosion resistance of selected MgO-C materials were tested with the use of induction furnace of medium frequency.     

Effect of Ti （C,N） on Properties of Low-carbon MgO- C Bricks

The effect of Ti （ C, N） on properties of low-carbon MgO - C bricks was investigated. The phase composition and the microstructure of the matrix of low-carbon MgO - C brick containing Ti （ C, N） were studied by XRD and SEM analysis together with EDS. The results showed that Ti （ C, N） distributed in the matrix of lowcarbon MgO - C brick uniformly after being treated at 1 600 ~C for 3 h in coke powder bed, and Ti （C, N） and MgO formed a solid solution. After the treatment at 1 600 ℃ for 3 h in coke powder bed, the bulk density and cold crushing strength of low-carbon MgO - C brick with Ti （ C, N） decreased, and the apparent porosity and linear change rate of specimens increased. The oxidation resistance of low-carbon MgO - C brick with Ti（ C, N） was superior to that of low-carbon MgO - C brick with no additives, but inferior to that of low-car- bon MgO - C brick with Al powder. The slag resistance of the specimen with Ti （ C, N） was excellent as well.     

几种钢包用含碳耐火材料对IF钢增碳的比较

通过感应炉试验分析了钢包渣线用3种碳含量不同的镁碳砖(C的质量分数分别为8.3%、15.5%和17.9%),钢包底用蜡石-碳化硅砖(C的质量分数为3.71%)以及实验室开发的MgO-Al2O3-SiC质钢包渣线浇注料(C的质量分数为4.07%)对IF钢增碳的影响,并对其增碳的机理进行了初步分析讨论。试验结果表明:渣线镁碳砖的碳含量越高,对IF钢造成的增碳量越大;包底蜡石-碳化硅砖对IF钢水的增碳量达到渣线镁碳砖的7.73倍;MgO-Al2O3-SiC质浇注料也对IF钢产生明显的增碳效果,不宜用作冶炼超低碳钢的钢包渣线材料。     

Thermal conductivity of MgO-C refractory ceramics: Effects of pyrolytic liquid and pyrolytic carbon black obtained from waste tire

In the present study, thermal conductivity and mechanical properties of MgO-C refractory ceramic bricks were investigated. Pyrolytic liquid and pyrolytic carbon black obtained from pyrolysis of waste tires were used as a resin and carbon source, respectively. The pyrolysis of the tires was conducted in a fixed bed reactor at the temperature of 500?°C with a 15?°C/min heating rate under nitrogen flow (0.5?lt/min). Before using in MgO-C refractory ceramic blends, pyrolytic products were purified with the acidic extraction methods which resulted in 61and 66?wt%. decreases in sulfur and ash contents in pyrolytic carbon, respectively. After this treatment of pyrolytic liquid, the sulfur content was reduced by 24?wt%. Eight different blends of MgO-C refractory ceramics consisting of different pyrolytic product contents were prepared, pressed, and tempered at 250?°C, and then characterized in terms of porosity, thermal conductivity, and density. The mechanical behavior of the samples was tested using a three-point bending test. Archimedes test was employed to determine the porosity and density. Surface properties of the bricks were analyzed by scanning electron microscopy (SEM). The obtained results were compared with a reference consisting of graphite and resin. The results revealed that mechanical and thermal properties of the developed bricks were highly sensitive to the porosity and the carbon source as well as the type of binder.     

Wear of MgO-C Refractories in EBT Type Furnaces Experienced at Iranian Mobarakeh Steel Plant

Mobarakeh Steel Company produces 3 million tons ofsteel annually with eight 180 tons EBT furnaces. Differ-ent types of magnesia-carbon refractories have been em-ployed at slagline during last 5 years. In the present studythe wear and corrosion of MgO-C refractories of these fur-naces have been studied via post-mortem analysis of usedbricks and the observation of operational effects. Laborato-ry corrosion tests were also arranged to investigate the effectof slag chemistry and the mechanism of chemical corro-sion. Characterization of different magnesia-carbon bricksclarified that the crystal size, type and chemistry of mag-     

Corrosion mechanism of MgO-C bricks used as linings in a vanadium extraction converter

To extend the service life of MgO-C bricks used as linings in vanadium extraction converters, their corrosion mechanism was investigated using stationary immersion and rotary crucible methods at 1673 K. The effects of oxides in vanadium slag were studied using the slag invasion method. The results showed that a decarburization layer was formed but was not effectively sintered under vanadium extraction conditions, resulting in it having a loose structure and poor binding strength. When slag-splashing technology was applied to protect the converter, the decarburization layer and slag-splashing layer easily fell off due to scouring by the molten pool. Consequently, the poor strength of the decarburization layer was the main reason for the poor anti-erosion performance of the MgO-C bricks and the weak effect of slag-splashing technology. In addition, higher contents of SiO₂ and TiO₂ in vanadium slag could form low melting point compounds and increase the thickness of the decarburization layer, thereby accelerating the MgO-C brick corrosion rate. Higher contents of FeO in the vanadium slag not only formed low melting point compounds but also caused a decarburization reaction with the MgO-C bricks. However, with increases of V₂O₃ in the slag, the formation of high melting point compounds decreased the corrosion rate and corrosion depths.     

低碳MgO-C耐火材料结构和性能优化的研究进展

MgO-C耐火材料作为钢铁冶炼用关键基础材料,被广泛用作转炉衬砖、电弧炉炉壁和钢包渣线用砖。寻求制备高性能低碳MgO-C耐火材料的新方法对耐火材料及冶金行业的发展至关重要,本文从纳米碳源的引入、骨料表面的改性和镁基骨料的引入、酚醛树脂的改性、抗氧化剂的引入及陶瓷相的原位形成角度出发,综述了改善低碳MgO-C耐火材料结构和性能的研究进展,以期为进一步推动低碳MgO-C耐火材料的发展提供参考,并对MgO-C耐火材料未来的研究方向进行了展望。     

精炼钢包渣线镁碳砖被侵蚀的显微分析

通过静态和动态抗渣实验,考查了精炼钢包用渣线镁碳砖被侵蚀的情况,并从显微分析的角度研究了镁碳砖被侵蚀的原因.研究表明,在静态实验中,镁碳砖中的氧化镁会溶解到熔渣中去,方镁石晶粒间的杂质在高温下形成低熔相成为熔渣侵入的通道并促进了该溶解过程.在动态实验中,由于镁碳砖中的石墨会溶解到钢水中,位于钢水和熔渣界面的熔渣进而渗透到镁碳砖中,加上钢水的冲刷等因素造成镁碳砖的损毁.     

Development of a Thermoplastic Magnesia Carbon Brick ——＂A Cold Process Flexible System＂

1IntroductionMagnesia carbon brick(hereinafter called MgO-C)was developed around30years back,and is nowwidely used in all steel making furnaces.Its use isgradually extended to different other area like tandemfurnace,RHdegasser etc.Conventionally such bric…     

Nano carbon containing MgO-C refractory: Effect of graphite content

Development of low carbon containing MgO-C refractories has been studied containing a fixed 0.9 wt% of nano carbon and 1–9 wt% of flake graphite. Refractory compositions were prepared and processed as per the conventional manufacturing techniques of MgO-C refractory. Properties of the different compositions were evaluated and also compared against the conventional MgO-C refractory containing 10 wt% graphite prepared under exactly similar conditions. Addition of 3 wt% of flake graphite in combination with 0.9 wt% of nano carbon black was found to be optimum and resulted in better/comparable properties to that of conventional MgO-C refractory.     

氧化铝微粉加入量对低碳镁碳砖性能的影响

以电熔镁砂、石墨、金属Al和氧化铝微粉为主要原料,热塑性酚醛树脂为结合剂,制备了w(C)5%的低碳镁碳砖试样,研究了氧化铝微粉加入量(其质量分数分别为0、3%、5%、7%、9%)对低碳镁碳砖的常温物理性能、抗热震性和抗氧化性的影响。结果表明:(1)随着氧化铝微粉加入量的增加,低碳镁碳砖试样的体积密度、常温强度和高温强度均先升高后降低,显气孔率则先降低后升高;抗热震性和抗氧化性随微粉加入量的增加呈先改善后变差的趋势;其中,微粉加入量为5%的低碳镁碳试样综合性能最好。(2)低碳镁碳砖试样性能的改善主要是由于加入的氧化铝微粉和MgO在高温下原位反应生成连续分布的尖晶石,增强了基质的陶瓷结合;但氧化铝微粉加入量过大时,由于大量原位反应引起材料产生过大的体积膨胀,会导致基质结构疏松,从而恶化镁碳砖的性能。     

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。     

Role of Calcium Magnesium Aluminate in Carbon-containing Bricks for Steel Ladle

Calcium magnesium aluminate,with the commercial name of MagArmour,is a synthetic material consisting of 70 mass%Al₂O₃,20 mass%MgO and 10 mass%CaO,approximately.It is characterized by porous microstructure,intergranular aluminates phases and micro-crystalline spinel.Since globally launched in 2017,MagArmour has been successfully applied to various carbon-containing refractories serving for steel refining process.Lots of cases have demonstrated the role of MagArmour in enhancing the service life of carbon containing bricks for ladle lining.The benefits embody in formation of protective coating on hot surface,relief of drilling corrosion in joint positions,and elimination of grooves or cracks caused by mechanical stress concentration.In addition,MagArmour is effective in protecting graphite from deep oxidization so as to be capable of replacing the metallic or carbide anti-oxidants in carbon-containing bricks entirely.By means of chemical analysis and microstructural dissection,postmortem investigations on the used MgO-C bricks from both metal and slag zones of 120t steel refining ladle were conducted to clarify the working mechanism of MagArmour.The formation of protective coating on hot face is attributed to the dissolution of micro-crystalline spinel into contacting slag,which changes the slag chemistry so as to enhance viscosity.The improvement in corrosion/erosion resistance is highly related to the porous microstructure and dispersive aluminates.As well known,evaporation of Mg,Al and SiO,and/or internal migration,occurs in MgO-C bricks at elevated temperatures.The gaseous phases are absorbed by MagArmour particles due to the high surface area of porous microstructure and condense as corresponding oxides.These oxides react with the intergranular calcium aluminates forming liquid phase.With increasing temperature,the liquid phase seeps into the matrix under capillary force.The increased liquid amount improves the flexibility of the matrix and thus releases the internal stresses concentration resulting from mechanical stress and temperature gradient.Meanwhile,densification of the matrix microstructure occurs under the static pressure generated by liquid steel and molten slag,which blocks the channels of oxygen infiltration.     

Effects of expanded graphite content on the performance of MgO-C refractories

Expanded graphite was introduced into a MgO-C refractory to suppress its thermal expansion and thus enhance thermal shock resistance. The refractory was prepared by mixing MgO powders (particle size = 75 μm and 1 mm), antioxidant and curing agents, flake and expanded graphite, and a novolak-type phenolic resin at 50°C. This was followed by aging at 20°C for 24 h, compacting by uniaxial pressing, curing at 210°C for 5 h, and heat treatment at 1500°C. With an increase in expanded graphite content from 0 to 4 wt.%, the bulk density decreased, apparent density remained unchanged, and apparent porosity increased. The gaps created in the vicinity of MgO particles because of this increase in apparent porosity buffered the thermal expansion of MgO. This increased resistance to thermal shock up to 1500°C. However, the increase in expanded graphite content also had a detrimental effect reflected in the decrease in fracture strength and increase in the residual strain after repeated thermal shock. This contradiction indicates that composition optimization is important for the practical performance enhancement of MgO-C bricks. The optimum content of the expanded graphite was determined as 2 wt.%.