Application of Semi—rebonded Magnesite—Chrome Bricks of LRF at RH Lower Vessl of NKK Keihin Wroks

The application results of semi-rebonded magnesite-chrome bricks at RH lowe vessel of NKK Corporation Keihin Works have been analysed,The results indicate that the main reasons that cause the damage of the refactory brcks include:chemical attack of slage to the semi-rebonded magnesite-chrome bricks;pene-tration of molten stel,slag into the bricks;and therma spalling due to temperature fluctua-tion during steel making operation.The results of multiple effection of these factors lead to alternative action of erosion(chemical attack and penetration)and spalling(thermal spalling and structure peeling) resulting in the damage of the brik ,In order to improve the performance of the bricks ,it is necessary to promote the resistance to erosion and thermal shock resistance as well as to keep the accurate dimensions of the brick,The measures of improvement of resistance to erosion of magne-site-chrome bricks taken by the researches mainly include:lowering the contents of impu-rities in the bricks(mainly including SiO2,CaO,and next Fe2O3 and Al2O3);promoting the extent of direct bond of the brick;forming a large amount of magnesia-chrome composite spinel well-distributed in the bricks through adding a large amount of synthesized materi-als;enhancing the resistance to erosion by adding a little amount of high-effective additives,Improvement of thermal shock resistance of the bricks is mainly through introducing some additive to make a certain amount of mi-cro-cracks occur in the brick so as to obtain an effect of increasing toughnes or through for-mation of second high temperature solid phase in the brick by adopting additive,In addition,it is needed to improve the quality of the brick appearance and ensure accurate dimensions of the brick,The purpose of this paper is to further iprove the service life of the refractory bricks by making use of the improvement mea-sures taken on the basis of the analysis results of the used bricks.     

Application of Semi—rebonded Magnesite—Chrome Bricks of LRCO at RH Lower Vessl of NKK Keihin Works

The application results of Semi-rebonded Magnesite-Chrome bricks at RH lower vessl of the NKK Corporation Keihin Works have been analysed.The results indicate that the main reasons that cause the damage of the refractory bricks include chemical at-tack of slag to the Semi-rebonded Magnesite-Chrome bricks;penetration of molten steel and slagn into the bricks;and thermal spalling due to teperature fluctuation during steel making operation. The re-sulits of multiple effection of these factors lead to alternative action of erosion(chemicl attack and penetration) and spalling (thermal spalling and structure peeling) resulting in the damage of the brick,In order to improve the performance of the bricks,it is necessary to promote the resistance to ero-sion and thermal shock resistance as well as to keep the aurate dimensions of the brick .The measures to improve the resistance to erosion of magnesite-chrome bricks taken by the researchers mainly in-clude:lowering the contents of impurities in the bricks (mainly including SiO2,CaO,and next Fe2O3 and Al2O3);promoting the extent of direct bond of the brick;forming a large amount of magnesia-chrome composite spinel well-distributed in the bricks through adding a large amount of synthe-sized materials ;enhancing the resistance to erosion by adding a little amount of high-effective addi-tives,Improvement of thermal shock resistance of the bricks is mainly through introducing some addi-tive to make a certain amount of micro-cracks occur-ing in the brick so as to obtain the effect of increase toughness or through formation of second high tem-perture solid phse in the brick by adopting addi-tive,In ddition,it is needed to improve the quality of the brick appearance and ensure accurate dimen-sions of the brick ,The purpose of this paper is to describe the further improvement of the service life of refactory brick by the measures taken on the basis of the nalysis results to the used bricks.     

Chemical Corrosion Mechanisms of Magnesite-chrome Bricks by Converter Slag

The corrosion resistance of four kinds magnesitechrome bricks against converter salg was investigated by static crucible slag tests. The microstructures of the asdelivered and tested refractories were analyzed by means of SEM and EDS. The results showed that： Different magnesite-chrome bricks have different slag resistances. Generally, the slag resiantance sequence is as follows： rebounded fused magnesite-chrome brick 〉 semi-reboun- ded magnesite-chrome brick 〉 direct-bonded magnesitechrome brick 〉 silicate bonded magnesite-chrome brick. Slag reacts with the periclase of magnesite-chrome refractories, which results in the dissoving of periclase in fayalite slag. However, the complex spinels have superior slag resistance.     

Study on Mechanism of Reaction Between AOD Slag and Rebonded Magnesite—Chrome Brick

The influence of the composition of AOD slag on the corrosion of rebonded magnesite-chrome brick has been studied by analyzing the residual bricks at the tuyere zone of AOD .It indicates that the corrosion degree increased with the increase of the basicity of slag and decreased with the increase of the content of MgO ,Cr2O3 and Al2O3 in slag.And the addition of refractories to slag up to satura-tion could decrease the corrosion abiliy of sag.It is important to make a resonable slagmaking rule and ensure the percentage of MgO in slag more than 11wt% for pro-longing the service life of lining.     

Corrosion and Penetration Resistance of Corundum Bricks to High Phosphorus Oolitic Hematite Reducing Materials

The paper aims at investigating whether corundum bricks can be used for the bottom of the direct reduction furnace of high phosphorus oolitic hematite. The reducing materials including high phosphorus oolitic hematite,bitumite,Ca(OH)_2 and Na_2CO_3 at a mass ratio of 1 0. 15 0. 15 0. 03 were mixed and pressed into carbon containing cylindrical specimens with the size of Φ 15 mm× 20 mm. The specimens were placed on the corundum bricks and reduced in a high temperature tube furnace at 1 200 ℃ for 40,60,80,140 and 220 min,respectively. The corrosion and penetration resistance of corundum bricks to high phosphorus oolitic hematite reducing materials were analyzed with XRD,SEM and EDS. It shows that the reducing slag formed in the reduction process corrodes the surface of corundum bricks to form a product layer of anorthite and hercynite,retarding the further corrosion of the reducing slag; the reducing slag which has penetrated into the interior of the brick goes through the gaps between the particles and generates anorthite and hercynite,filling the gaps and hindering the reducing slag penetration.     

Development of Semi—Graphite Carbon—Silicon Carbide Brick and Its Application in Slag Forming Zone of Large—sized Blast Furnace

Based on the damage mechanism of the lining at the slag forming zone of the blast furnace and the charactieristics of various refractory ma-terials,the methods to increase the service life of the lining at the slag forming zone have been found:(1) to improve the capacity of the blast furnace brick lining subjet to heat impact;(2) to reduce the working side temperature of the brick lining.On this basis,the semi-graphitized ,high temperature electrically calcined anthracite and silicon carbide etc ,were used as the main raw materials,Through a lot of experiments the proper raw material mix and grain size compo-sition were determined,In addition ,a suitable amount of additives and binders was added.After high pressur forming,high temperature firing and grinding ,the semi-graphitic carbon-silicon carbide bricks with close dimension tler-ances and ideal physical and chemical properties have been made.They have been applied in some blast furnaces,such as No.11(2580 m^3) and No.6(1050 m^3) blast furnaces etc.at Anshan Iron and Steel Company,and the problem of short service life at slag forming zone of blast furnace has been solved.     

A Discussion on Stability of Mg-Al-spinel Crown of Glass Melters

In order to understand the failure mechanism of magnesia-alumina spinel crown of glass melters,a discussion on the stability of Mg-Al-spinel crown of glass melters was given in this paper.The discussion focused on the weight balance in the crown arch made of spinel or silica bricks,the creep of spinel crown bricks at high temperatures,the thermal stress distribution in crown bricks as well as at brick joints,and the displacement behavior of crown arch during heat-up of glass melter.It is believed that the tangential stress in spinel crown is much higher than that in silica crown due to the large differenee in their densities,and that the thermal stresses in the crown brick result in opening of a part of the brickto-brick joints at the cold side of the crown,and increase of the tangential stress needed for balancing the weight of the crown.Both defect migration in lattice or along grain boundary and viscous flow in glass phase at grain boundary contribute to the creep of crown bricks at high temperatures.The creep of the matrix of spinel brick is more significant than that of coarse grains because impurities,such as silica and calcia,are concentrated in it.For keeping the crown stable during heat-up period it is important to adjust properly the horizontal positions of each skew brick as temperature increasing based on correctly evaluating the thermal expansion according to the thermal expansion coefficient of the crown brick.     

Development of Long Life Magnesia—carbon Brick for UHP Electric Arc Furnace

The corrosion mechanism of high ferric oxide slag to the magnesia-carbon brick for UHP furnace was analyzed,and the magnesia-carbon brick with high ferric oxide slag resistance was develped by selecting specially processed fused magnesite and changing size distrbution and the additives.The magnesia-carbon brick has good affinity to the slag and could adhere the slag efficiently in usage,It has better slag corrosion resistance and high temperature strength than the ordinary magnesia-carbon brick It showed better adaptable to the high ferric oxide slag when it was first used in 1999 in 150t UHP furnace of Tianjing Steel Pipe Company ,and achieved 400 heats service life.     

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.     

Comments on Modification of International Standard －Refractory bricks－Dimensions

Comments on modification of International standard ISO 5019/1,5019/2,5019/3 relating to the dimensions of rectangular bricks,arch bricks and rectangular checker brick for regenerative funaces have been put forward.It is considered that the thickness dimensions of the bricks in these international standards should be revised because they are converted from inch and are not multiples of 5,which brings some problems for bricklaying.The disance be-tween the big end and small end of arch bricks should be paid more attention.     

Slag erosion-resistant coating for periclase-magnesia-aluminum spinel brick

The magnesia-carbon bricks are used at the ladle slag line adds carbon to molten steel and thus has an adverse effect on the smelting process. Steel production enterprises hope to remove carbon from the ladle slag line. This study presents a Silica sol (SS)–magnesium aluminate spinel(MA) coating that can be applied to the surfaces of periclase–MA spinel brick (spinel brick) to improve their slag erosion resistance, facilitating the elimination of carbon from the ladle slag line. The slag corrosion resistance mechanism of a spinel brick covered with the SS–MA coating was analyzed through scanning electron microscopy and simulation using FactSage software. The results show that increasing the SS content (C_SS) led to the formation of fine cracks during the coating-drying process and was detrimental to the slag erosion resistance of the coating. The optimum C_SS was 20%. In the high-temperature slag erosion experiment, the MA in the coating was capable of forming solid solutions with Fe and Mn in the slag, and the nano-SiO₂ in the coating interacted with the slag, increasing the viscosity of the slag and reducing its penetration. In addition, the presence of the coating extended the penetration path of the slag and reduced the contact area between the slag and the spinel brick and their chances to undergo chemical reactions, thereby protecting the spinel brick from slag erosion. The coated spinel bricks outperformed the magnesia-carbon brick in terms of slag erosion resistance, providing a basis for selecting carbon-free refractory materials for the ladle slag line.     

锰渣与再生砖骨料制备免烧砖的性能及应用

锰渣与再生砖骨料均属于大宗固废,提升大宗固废利用率具有重要的环境效益和经济效益。本文利用锰渣、再生砖骨料等制备了免烧砖,探究了锰渣掺量对免烧砖各项性能的影响,且对其微观结构及有害物质浸出行为进行了分析。结果表明:制备的免烧砖外观质量优良,色泽均一,尺寸标准;结合强度要求和抗冻性要求,锰渣掺量不超过10%(质量分数)时,可制备出强度、耐水性和耐久性优异的MU20免烧砖,锰渣掺量不超过15%时,可制备出性能优异的MU15免烧砖;掺适量锰渣的免烧砖中形成了较多的钙矾石相,有利于强度发展。锰渣和再生砖骨料制备的免烧砖可以应用于人行道等市政工程,应用效果良好。研究结果可为锰渣低碳资源化利用以及生态砖制品的生产和应用提供技术支持。     

气化炉用后高铬砖的渣蚀机理

采用扫描电镜和XRD等分析方法,对石油焦气化炉和水煤浆气化炉用后高铬砖及渣蚀试验砖的显微结构进行了观察与分析。根据高铬砖显微结构变化,研究了在不同气化炉内高铬砖受熔渣侵蚀损毁的机理。结果表明:石油焦气化炉用高铬砖中的Cr2O3与熔渣中的V2O5接触反应,在低温下形成液相而被熔蚀,是其蚀损的主要原因;水煤浆气化炉用高铬砖蚀损的主要原因是Cr2O3在熔渣里的溶解和ZrO2的熔蚀;LIRR-HK95砖由于成分和结构的优化,抗石油焦渣侵蚀性能好。     

4喷嘴对置式气化炉耐火砖蚀损影响因素浅析

简述了4喷嘴对置式气化炉耐火砖的结构形式和蚀损情况;分析介绍了其使用寿命短的影响因素及相应的技改措施：①气化炉烧嘴空间偏小,应增加气化炉长径比;②烧嘴物料喷入速度偏高,应控制其喷入速度;③拱顶耐火砖预制块结构不合理,则应改造其结构;④熔渣侵蚀,则砖壁应保留一定量的固态渣;⑤热应力破坏,则应保持稳定操作。结果表明：技改后气化炉拱顶砖的使用寿命由最初的780h提高到超过4300h。     

EXPERIMENTS IN DEAD-BURNING DOLOMITE AND MAGNESITE1

Stability of calcined dolomite; effect of fineness of raw material, nature of flux and temperature of burning .—Dolomite is difficult to dead-burn because the absorption of moisture from the air produces a gradual slacking due, probably, to the hydration of lime and various lime compounds, and this tends to cause disintegration. With all the fluxes tried, 100 mesh raw material gave greater resistance to slacking than 8 mesh size. This resistance decreased, however, with increasing temperature of calcining, by an amount which seems to depend on the silica and alumina content of the flux, being greatest for basic open hearth slag and kaolin, less for flue dust, and iron ore, and least for roll scale. The stability also varied with the proportions of flux used, being greater, as a rule, for smaller proportions. Shrinkage, porosity and vitrification of calcined dolomite; effect of flux and burning temperature .—The shrinkage and porosity curves for mixtures containing flue dust, iron ore or roll scale are very similar. The higher the proportion of flux, the lower the temperature required to get maximum shrinkage and minimum porosity. Kaolin and basic open hearth slag behaved peculiarly in that vitrification depended more on the burning temperature than on the proportion of flux used. Experiments in making dolomite brick .—It was found that ageing of the wet calcined material was necessary to prevent cracking of the bricks upon drying. With 5 per cent MgCl₂ as binder, comparatively strong brick were obtained. High shrinkage on firing caused excessive cracking, but the bricks were extremely dense and did not disintegrate until after four to six months. Unfired tar-bonded brick were made with sufficient strength to stand shipping and with a storage life of about four months. Fired tar-bonded brick showed less shrinkage and cracking than similar brick made with water. If dipped in tar to protect them from moisture, such brick will last five or six months before disintegration. It is possible, then to make dolomite brick with a storage life long enough to allow shipping and placing in furnaces. Stability, shrinkage and porosity of calcined magnesite; effect of flux and temperature of burning .—Unlike dolomite, magnesite showed less slacking effect the higher the temperature of burning. Roll scale gave greater stability than iron ore, probably because of its lower silica content. The product was comparatively porous and with low shrinkage, even with high proportions of roll scale.     

Behavior of magnesia bricks in furnaces for the production of manganese alloys

Conclusions The application of dense magnesia bricks contributes to increased durability of the lining in metal manganese and manganese slag producing furnaces.The life of magnesia brick linings with an 11 to 13% porosity amounts to 45 days.The employment of large-size bricks hightens the resistance of the furnace bottom.Periclase-spinel brick proved unsuitable in the production of manganese slag.It is suggested that bricks with a porosity of 14 to 16% be tested for the purpose of determining optimal porosity.     

Post-mortem analysis of MgO–Al2O3–C bricks containing bauxite used in steel ladle walls

A serious problem with integrated masonry linings ladle was that the ladle wall bricks were difficult to be partially replaced. Thus, the service life of the ladle was determined by the properties of ladle wall bricks. In this study, the new generation of MgO–Al₂O₃–C bricks with bauxite aggregates was tested in a ladle lining of an integrated steel ladle for 103 cycles, and the corroded microstructure of the used brick was investigated. A multilayered structure of bauxite aggregates could be observed in the used brick, which inhibited the slag penetration along the boundary of the magnesia aggregates and reduced the degree of the aggregates fall off from the used bricks. Besides, during the process of slag penetration, bauxite aggregates could melt into the slag, which increased the viscosity of the slag and weakened the penetration ability of the slag. The MgO–Al₂O₃–C bricks with bauxite addition could improve the service life of the ladle to a certain extent.     

镁锆砖和镁铬砖的抗RH炉渣侵蚀性对比

为取代RH炉用镁铬材料,以电熔镁砂为主原料,分别加入单斜锆、脱硅锆、单斜锆与脱硅锆的混合粉、锆英石制备了ZrO2质量分数分别为15%和20%的镁锆砖,并利用静态坩埚法对比研究了镁锆砖和镁铬砖的抗RH炉渣侵蚀性。结果表明:对于Al2O3含量高且碱度(CaO/SiO2比)大的RH炉渣,镁锆砖抗侵蚀性能优于镁铬砖的;镁锆砖的侵蚀机理是砖中的ZrO2与渣中的CaO迅速反应,形成高熔点物相CaZrO3,能堵塞砖中的孔隙而形成致密保护层,从而阻止钢渣对镁锆砖的进一步侵蚀;而镁铬砖的侵蚀机理是渣中的Al2O3、Fe2O3等R3 和镁铬尖晶石中Cr3 交换,渣与砖反应生成的镁铝尖晶石和镁铁尖晶石使得材料变性,同时由于体积效应使镁铬材料鼓胀开裂,从而导致镁铬砖的严重侵蚀。     

Study on Microstructure and Slag Corrosion Mechanism of High Chrome Bricks for Gasifier

1 Introduction The gasifier like Texaco style is of important tech- nical equipment for ammonia synthesis and production of carbamide, carbinol and ethylene etc. Due to differ- ent energy resource structure, petroleum coke is adopt- ed as rawmaterial in A…