Casting Simulation of Calcium Titanate and Calcium Zirconate Nozzles for Continuous Casting of Aluminum-Killed Steels

The clogging of submerged entry nozzles (SENs) and tundish well nozzles is a common problem in the continuous casting of aluminum-killed steels. Clogging occurs when alumina attaches to the inside of the nozzle restricting the flow. This article explores the use of new nozzle materials that could prevent accretion growth through the formation of liquid phases at the inclusion-refractory interface. Casting simulation experiments were conducted using three nozzle refractory formulations: calcium titanate, calcium zirconate, and a 2:1 calcium titanate to calcium zirconate molar mixture. Nozzles fabricated from these materials cast more aluminum-killed steel without clogging than typical industrial alumina graphite nozzles. However, the nozzles constructed of calcium titanate dramatically outperformed alumina graphite, calcium zirconate, and the mixed nozzles. Microscopy investigation of spent nozzles found no accretion formation in the calcium titanate nozzles. The performance difference was due to the formation of a liquid calcium aluminum titanate phase, which prevented alumina accretions.     

Transient Inclusion Evolution During Modification of Alumina Inclusions by Calcium in Liquid Steel: Part I. Background,Experimental Techniques and Analysis Methods

In aluminum-killed steels, modification of solid alumina inclusions is often carried out by calcium treatment, converting the alumina to liquid calcium aluminates. When calcium treatment is performed, calcium can either react with sulfur in the melt or with solid alumina. Calcium sulfide inclusions are solid at steel casting temperatures and thus would be detrimental to castability if they remained in the steel after calcium treatment. The aim was to study the transient evolution of inclusions after calcium treatment, testing the hypothesis that calcium sulfide may form as an intermediate reaction product, which can subsequently react with alumina to form modified calcium aluminates. The first part gives the project background and describes the experimental and quantification techniques adopted, including the effect of sampler size in laboratory melts. Results of the formation of intermediate calcium reaction products in laboratory and industrial heats are presented in the second part.     

包钢小方坯连铸过程中的水口堵塞

中间包浸入式水口的堵塞是铝镇静钢连铸过程中普遍存在的问题,对于小方坯来说,问题尤为严重.包钢炼钢厂采用80 t转炉,钢包精炼炉(LF炉)和六流小方坯连铸机生产铝镇静钢.针对浸入式水口堵塞的问题,通过对LF炉精炼过程的优化,改善了钢水的浇铸性能,保证了小方坯铸机的顺利生产.     

Development of indices for quantification of nozzle clogging during continuous slab casting

Abstract

Deposition of alumina inclusions inside the submerge entry nozzle is a long standing problem in continuous casting of aluminium killed steel. Clogging of the casting nozzle severely affects productivity and also causes degradation of product quality. Unfortunately, very few numerical tools are available for precise quantification of the magnitude of clogging. Tools for quantifying the extent of clogging were developed during the present work and have been integrated with the control system of a running continuous slab casting shop. Reasonable match has been observed between the estimation from the developed program and the actual observations in the casting shop and subsequent products. In addition to process control, the tools were also found useful for comparing the castability of different steel grades. This feature has been utilised to study nozzle clogging during casting of steel grades that are commonly believed to have poor castability.     

铝锆碳浸入式水口异常堵塞原因分析

对钢液微合金化钛处理后引起堵塞的铝锆碳质浸入式水口进行分析,结果表明:堵塞物质为铝酸钙和钙钛矿。铝酸钙有变质体中的析出相,也有水口内壁处的原位反应产物,还有钢液中内生夹杂物。中包渣渗有钛处理和铝处理后的残留物,改变了原有属性,导致水口边滞留,为新生高熔点物质铝酸钙提供了物质来源,新生和内生铝酸钙及钙钛矿共同引起水口结瘤导致堵塞。     

Effect of Nozzle Base Material on the Rate of Clogging during the Continuous Casting of Aluminum‐Killed Steels

One approach to solving the problem of nozzle clogging during the continuous casting of aluminum‐killed steels is through careful selection of nozzle materials. In this study, the rate of clogging was measured while casting steel through simulated nozzles produced from alumina, zirconia, magnesia, zirconia‐graphite, and alumina‐graphite ‐ three common base materials and two common carbon‐containing nozzle materials. Spent nozzles were characterized using optical and cathodoluminescence microscopy. Interactions between the nozzles and steel were not observed in the alumina, zirconia, and zirconia‐graphite nozzles. Slight interactions were observed in the magnesia nozzles as alumina inclusions within the steel interacted with the nozzle to produce alumina‐magnesia spinel. Greater amounts of interaction were observed with alumina‐graphite nozzles. No statistical differences in the mean rate of clogging were observed between all of the pure oxide nozzles and zirconia‐graphite nozzles. However, the alumina‐graphite nozzles clogged at a much higher rate than the other nozzles. The higher rate of clogging is thought to be due to refractory‐steel interactions.     

Fluid flow and heat transfer with nail dipping method in mould during continuous casting process

ABSTRACT

The character and cause of sliver defect on IF steel sheet surface are studied by means of SEM, unstable flow in mould could induce surface velocity and level fluctuations, leading to surface defects during continuous casting of steel. The nozzle clogging is a serious problem during the continuous casting of steel, due to its influence on the casting operations and products quality. In this study, the nail dipping method for measuring surface velocity and flow direction in molten steel were employed. The fluid flow in mould of whole casting sequence was investigated, especially during the nozzle clogging conditions. The results showed that when nozzle clogging occurred in the 7th heat, the flow velocities on R and L side of nozzle were 0.280 and 0.402?m/s, respectively. The surface defect ratio of hot-rolled and cold-rolled plates increases with the increase of heat flux deviation on both sides of the mould copper. The different clogging per cent on both sides of the nozzle will lead to asymmetry flow, the surface velocity is higher with the small clogging per cent side compared to that of relatively large per cent clogging side.     

Influence Factors of SEN Clogging of Rare-Earth Steel Continuous Casting and Solve Ideas of Japanese Steel Enterprises

The clogging behavior of submerged entry nozzle (SEN) is the main reason restricting the continuous casting of steel, which seriously affects the application and popularization of rare-earth (RE) steel. Through literature analysis, herein, the main influencing factors and mechanism of RE steel continuous casting immersion outlet clogging, and sorts out the main ideas and practices of relevant Japanese enterprises in solving SEN clogging in recent years, are summarized, mainly including the following: 1) optimizing SEN materials to reduce nozzle clogging reactions; 2) using Ar-blowing SEN; 3) applying electromagnetic field to eliminate charge and inhibiting clogging reaction; and 4) and regulating the composition of molten steel to reduce the possibility of clogging, etc. The combination of these advantages and measures is a feasible way to solve the nozzle clogging of RE steel continuous casting nozzle.     

铝镇静冷镦钢CaS结瘤机理及改进

 对铝镇静冷镦钢在浇铸过程中出现的浸入式水口结瘤问题进行了系统研究,结瘤物中主要为C12A7(12CaO·7Al₂O₃)、CaS以及少量的MgO、TFe等,CaS所占比例达到36.91%,CaS含量过高,是造成水口结瘤的主要原因。结合生产过程分析发现,当钙处理时钢水中硫含量偏高,或喂入钙含量过多时,则生成大量的CaS夹杂,促使水口结瘤。通过改进脱氧造渣工艺、优化钙处理工艺等一系列措施,将钙处理前钢水中硫质量分数控制在0.005 0%以下,钙处理后钢水中钙质量分数控制在0.001 4%～0.002 6%,使钢水中Al₂O₃夹杂改性充分,同时避免生成CaS夹杂造成水口结瘤,有效解决了CaS夹杂引起的水口结瘤问题,提高了铝镇静冷镦钢钢水浇注性能,使连浇炉数由最低的10炉/中间包提高至16炉/中间包以上。     

生产轴承钢用浸入式水口的堵塞机理

 由于生产轴承钢水口的堵塞,严重影响生产的顺利进行。利用化学分析、相分析和岩相分析的方法对浸入式水口堵塞物及其耐火材料进行研究。结果表明,发生水口堵塞的位置主要在水口渣线部,堵塞物化学成分主要以金属Fe为主,其它含有Al、Cr、Si、C等物质。而水口内壁物质主要是Al2O3、SiO2、CaO、Cr2O3、FeO等氧化物。从X射线分析看,这些物质主要是熔点较高的CaO和Al2O3形成的CaO·2Al2O3和CaO·6Al2O3。由此分析得出,钢水金属冷凝、连铸保护浇铸不好和钢水不洁净是造成水口堵塞的主要原因。同时给出了防止水口堵塞的技术措施。     

连铸中间包水口堵塞机理及防止措施

介绍了连铸中间包水口堵塞的主要类型,总结分析国内外关于Al2O3黏附堵塞的机理及其防止措施的研究现状,并讨论防止水口堵塞措施的研究方向。针对水口堵塞问题,国内外开展了多方面防止水口堵塞措施的研究,取得了一定的效果,但水口堵塞问题仍未得到彻底解决。前人的研究结果表明,改进水口材质是可能从根本上解决水口堵塞的方法。目前,单一材质已不能满足连铸发展的要求,多样化、复合化是水口材质的发展趋势,其中碱性的尖晶石材料和低浸润材料将是重要的方向。夹杂物向水口内壁传递是水口堵塞的控制性环节,由于钢液高温不可见,目前多采用数值模拟方法进行研究。基于EDEM-FLUENT耦合的模拟方式可以更客观地描述夹杂物颗粒传递过程和考虑颗粒间的相互作用,将是数值模拟研究高熔点质点黏附机理的一个重要方向。     

连铸中间包上水口及浸入式水口结瘤物分析

水口结瘤一直是困扰连铸生产的问题,对连铸生产中发生结瘤的中间包上水口和浸入式水口从上到下做了全面的解剖分析,通过SEM、EDS、X-RD等手段对水口的结瘤物进行分析研究。结果表明,中间包上水口结瘤严重,钢水完全凝结;在浸入式水口渣线以上,发生了严重的结瘤,厚度约为16 mm,渣线下的结瘤较轻,结瘤物主要是Al2O3夹杂着钢水凝结而成,由于钢水中的酸溶铝含量较高,水口处Al2O3的富集使钢水凝结,堵塞水口。根据研究得出,中间包上水口和浸入式水口结瘤堵塞的原因为钢水酸溶铝含量较高,钢水在水口处温降过大、拉速过低等。     

Clogging in submerged entry nozzles

Casting high quality steel grades requires the use of a submerged entry nozzle (SEN) to prevent oxygen and nitrogen pick‐up and to achieve favourable steel flow conditions in the mould. Clogging of the SEN leads to instability of the casting operation as well as to a decrease in slab quality. To understand the interactions between liquid steel and the SEN, 156 nozzles from the Sidmar steel plant were investigated with respect to the amount of clogging. A linear relation between the clogging volume and the clogging weight was observed. This indicates that the clogging material's density remains constant during the clogging process for the different steel grades. A distinct relationship was also found between the amount of clogging and the cast steel weight. No relation between the amount of clogging and the superheating of the steel nor the steel flow rate was noticed, however. It was also concluded that for AI killed steels the high Mn (> 3000 ppm) and high C (> 500 ppm) grades cause less clogging than AI killed steel grades with low Mn content (< 3000 ppm) and that Al/Si killed steel grades cause less clogging when compared to AI killed steel grades. When comparing these different steel grades with respect to their total oxygen concentration in the ladle, it appears that steel grades, which have a low total oxygen concentration, cause less clogging in the SEN. Based on these observations three combinations SEN/steel grade were selected for further analysis with electron microscopy.     

改善321含钛钢水口堵塞及结晶器“结鱼”现象的工艺实践

针对浙江永兴不锈钢股份有限公司321连铸易堵塞水口及结晶器结鱼问题,进行理论研究及现场随炉试验,通过一系列工艺改善来提高钢水纯净度,降低钢水中[N]及[O]的含量,同时适当调整连铸操作工艺,最终冶炼出较高纯净度的钢水：熔炼样钢水[N]≈0.01%,[O]≈0.0028%,成品夹杂物等级控制在国家标准范围内（GB/T 10561）,从结果来看,连铸水口堵塞现象大大改善,结鱼现象消失,顺利实现了两炉以上连浇,同时铸坯表面及内部质量良好,符合后续轧制要求。     

界面活性元素对低碳钢连铸过程水口结瘤的影响

水口结瘤问题是低碳钢、超低碳钢连铸过程中亟需解决的关键问题之一,其直接影响铸坯质量及生产过程顺行.从水口结瘤机理的角度出发,介绍了界面活性元素的基本含义及当前的研究方向,总结了常见的界面活性元素,并比较了连铸中界面活性元素对两相间润湿性及夹杂物形态、尺寸、分布的影响,分析了界面活性元素对水口结瘤的影响机制,对预测实际生...     

Ti对超低碳钢浸入水口堵塞的影响

针对鞍钢股份有限公司炼钢总厂2150 ASP中薄板坯铸机在浇注含Ti超低碳钢时水口堵塞严重的问题,分析了超低碳钢中Ti含量对水口堵塞的影响,通过优化RH工艺、顶渣改质、保护浇铸及提高耐材烘烤温度等措施,铸流换水口的频率由原来的平均1.7次/浇次降低到1.2次/浇次,单支浸入式水口的使用寿命由原来的平均88 min延长到119 min。     

Interracial Fluctuation Behavior of Steel/Slag in Medium-Thin Slab Continuous Casting Mold With Argon Gas Injection

The flow field of molten steel and the interfacial behaviour between molten steel and liquid slag layer in medium-thin slab continuous casting mold with argon gas injection were studied by numerical simulation, in which the effects of nozzle submergence depth and port angle, casting speed, and argon gas flow rate on the flow and the level fluctuation of molten steel were considered. The results show that the molten steel is jetted from the submerged entry nozzle (SEN) with three ports into the mold and forms three recirculation zones including one upper recirculation zone and two lower recirculation zones. Argon gas injection results in a secondary vortex flow in the upper zone near the nozzle. For a given casting speed and argon gas flow rate, increasing the side port angle and submergence depth of nozzle can effectively restrain the steel/slag interfacial fluctuation. Increasing the casting speed would prick up the level fluctuation. For a fixed casting speed, argon gas flow rate has a critical value, the interfacial fluctuation with argon gas injection are stronger than the case without argon gas injection when the argon gas flow rate is less than the critical value, but when the argon gas flow rate exceeds the critical value, the level fluctuation is calmer than that without argon gas injection.     

Interfacial Fluctuation Behavior of Steel/Slag in Medium-Thin Slab Continuous Casting Mold With Argon Gas Injection

 The flow field of molten steel and the interfacial behaviour between molten steel and liquid slag layer in medium-thin slab continuous casting mold with argon gas injection was studied by numerical simulation, in which the effects of nozzle submergence depth and port angle, casting speed, and argon gas flow rate on the flow and the level fluctuation of molten steel were considered. The results show that the molten steel jet from the submerged entry nozzle (SEN) with three ports into the mold and form three re-circulation zones including one upper re-circulation zone and two lower re-circulation zones. Argon gas injection results in a secondary vortex flow in the upper zone near the nozzle. For a given casting speed and argon gas flow rate, increasing the side port angle and submergence depth of nozzle can effectively restrain the steel/slag interfacial fluctuation. Increasing the casting speed would prick up the level fluctuation. For a fixed casting speed, argon gas flow rate has a critical value, the interfacial fluctuation with argon gas injection are stronger than the case without argon gas injection when the argon gas flow rate is less than the critical value, but when the argon gas flow rate exceeds the critical value, the level fluctuation is calmer than that without argon gas injection.     

中薄板坯流程生产IF钢中包水口结瘤控制

采用扫描电镜、能谱分析等方法,对BOF-RH-CC中薄板坯流程生产含钛IF钢浸入式水口结瘤的原因进行了分析。结果表明,含钛IF钢水口结瘤的原因为水口本体内部的C与SiO2发生反应产生氧化性气体,氧化性气体和钢水中的[Al]、[Ti]反应在水口内壁上形成反应层,反应层促进了钢水中原有的Al2O3和Al-Ti-O复合夹杂物快速向水口内壁沉积。Ti的存在加重了水口结瘤的发生。以全流程氧位控制为目标,通过转炉终点控制、RH精炼、顶渣改质、中薄板坯连铸等工艺优化,使RH出站钢水T[O]质量分数控制在35×10^-6以下,中包钢水T[O]质量分数控制在30×10^-6以下,水口结瘤现象得到明显改善,单支水口平均连浇炉数由1.2炉提高至3炉,单支水口连浇时间提高到177 min。