Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (I) ‐ Decarburization Process and Influences of Some Technological Factors

A novel three‐dimensional mathematical model proposed and developed for the non‐equilibrium decarburization process during the vacuum circulation (RH) refining of molten steel has been applied to the refining process of molten steel in a 90‐t multifunction RH degasser. The decarburization processes of molten steel in the degasser under the conditions of RH and RH‐KTB operations have been modelled and analysed, respectively, using the model. The results demonstrate that the changes in the carbon and oxygen contents of liquid steel with the treatment time during the RH and RH‐KTB refining processes can be precisely modelled and predicted by use of the model. The distribution patterns of the carbon and oxygen concentrations in the steel are governed by the flow characteristics of molten steel in the whole degasser. When the initial carbon concentration in the steel is higher than 400 · 10⁻⁴ mass%, the top oxygen blowing (KTB) operation can supply the oxygen lacking for the decarburization process, and accelerate the carbon removal, thus reaching a specified carbon level in a shorter time. Moreover, a lower oxygen content is attained at the decarburization endpoint. The average contributions at the up‐snorkel zone, the bath bulk and the free surface with the droplets in the vacuum vessel in the refining process are about 11, 46 and 42% of the overall amount of decarburization, respectively. The decarburization roles at the gas bubble‐molten steel interface in the up‐snorkel and the droplets in the vacuum vessel should not be ignored for the RH and RH‐KTB refining processes. For the refining process in the 90‐t RH degasser, a better efficiency of decarburization can be obtained using an argon blow rate of 417 I(STP)/min, and a further increase in the argon blowing rate cannot obviously improve the effectiveness in the RH refining process of molten steel under the conditions of the present work.     

120 t RH-LF生产低碳钢QD08的工艺实践

介绍了芜湖新兴铸管有限责任公司炼钢厂采用RH-LF精炼法生产低碳钢QD08的工艺实践。通过对转炉出站钢水初始条件,RH真空脱碳原理和过程控制,后续LF冶炼3个方面的分析研究,结果表明,初始钢水控制条件为[C] 0.04%～0.10%,[0]>300×10^-6,转炉终点出钢温度T≥1 650℃。随真空处理时间延长,真空度降低,真空室内PCO减少,碳氧浓度积呈降低的趋势,真空室内因发生碳氧反应进行脱碳,RH真空脱碳满足热力学条件;脱碳速率的变化规律为先增大后减小,脱碳速率有一定的规律;RH真空处理后的钢水需在LF完成脱硫、升温、合金化等操作,并且需保证终渣量20～23 kg/t,终渣（FeO）+（MnO）<1.2%,碱度R≥3.5等工艺条件。     

RH真空精炼过程的动态模拟

建立了描述RH真空精炼装置内钢液动态脱碳（脱气）模型。对RH真空精炼时的脱碳、脱氧、脱氮和脱氢过程进行了动态模拟研究，考察了浸渍管直径、循环流量、吹氩量、氧含量和真空度对脱碳和脱气过程的影响。动态脱碳（脱气）模型考虑了反应机理，认为脱碳是通过上升管中Ar气泡表面、真空室中钢液的自由表面和真空室钢液内部脱碳反应生成的CO气泡表面进行的，并且考虑了精炼处理时的抽真空制度。该模型能全面描述RH精炼过程中不同时刻钢液中碳、氧、氮和氢的含量，能较好预测实际过程，可用于RH真空精炼过程的优化和新工艺开发。     

RH吹氧操作对超低碳钢脱碳速率的影响

以迁钢RH精炼炉为背景,建立了RH强制脱碳数学模型,确定了脱碳的4个反应地点:真空室内钢液自由表面,氩气表面,真空室钢液内部与飞溅液滴表面,并进行了RH强制脱碳机制研究。模型计算结果表明,在真空处理前期,钢液内部脱碳速率在4个脱碳地点中占据主导地位,而在后期以液滴脱碳为主;在迁钢现有的压降模式下,确定了第3分钟进行吹氧操作,保证40m3/min的吹氧流量为最佳的工艺处理方式,并通过迁钢实际生产炉次的对照验证了模型计算结果。     

Modeling of Liquid Level and Bubble Behavior in Vacuum Chamber of RH Process

In the Ruhrstahl-Heraeus (RH)refining process,liquid steel flow pattern in a ladle is controlled by the fluid flow behavior in the vacuum chamber.Potassium chloride solution and NaOH solution saturated with CO 2 were respectively used as a tracer to investigate the liquid and gas flow behaviors in the vacuum chamber.Principal compo-nent and comparative analysis were made to show the factors controlling mixing and circulation flow rate.The liquid level and bubble behavior in the vacuum chamber greatly affect fluid flow in RH process.Experiments were per-formed to investigate the effects of liquid steel level,gas flow rate,bubble residence time,and gas injection mode on mixing,decarburization,and void fraction.The results indicate that the mixing process can be divided into three re-gions:the flow rate-affected zone,the concentration gradient-affected zone,and their combination.The liquid steel level in the vacuum chamber of 300 mm is a critical point in the decarburization transition.For liquid level lower than 300 mm,liquid steel circulation controls decarburization,while for liquid level higher than 300 mm,bubble behavior is the main controlling factor.During the RH process,it is recommended to use the concentrated bubble injection mode for low gas flow rates and the uniform bubble injection mode for high gas flow rates.     

Mathematical Model of RH Blow Argon Mode Affecting： Decarburization Rate in Ultra-Low Carbon Steel Refining

 A mathematical model in present study has been established to investigate the effect of Rheinstahl Heraeus (RH) blow argon mode on the decarburization rate in ultra-low carbon steel refining based on the RH equipment of Shougang Qian′an Iron and Steel Co Ltd (SQISCO). The calculated results show that the increase of argon flowrate promotes the carbon elimination from argon gas bubble surface, molten steel free surface in vacuum as well as splash droplet surface, while reduces that from the interior of liquid steel. It has been found the critical turning point of flowrate ascension is at the 5th minute and the optimum blow argon flowrate in later stage is 2100 L/min in accordance with the 2 stages argon blow mode, which have been confirmed in the commercial production in SQISCO.     

武钢120t RH炉MFB顶枪的应用

介绍了120 t RH炉MFB顶枪在真空室烘烤、去除真空室积渣及吹氧脱碳等方面的应用;考察了真空室预热烘烤煤氧比和流渣煤氧比,得出其最佳值分别为1∶0.75和1∶1.5;讨论了真空脱碳过程中合适的吹氧量,认为[O]质量分数保持在200×10-6以上,可以避免对脱碳速度的制约;另外,还讨论了挽救低温钢水事故过程中合适的加铝量及升温效果。     

RH真空室内气泡行为的研究

Ruhrstahl-Hereaeus (RH)上升管内的气液两相流是整个装置的重要动力源,并对钢液的流动、混匀及精炼过程有重要影响.上升管及真空室内的气液两相流决定了钢包内钢液的流动状态,为了研究真空室及上升管内气液两相流,通过1:6的300 t RH的物理模型模拟了RH上升管及真空室内气泡行为过程,并测量了RH循环流量的变化用于计算上升管内含气率以及气泡运动速度最终得到气泡在真空室内的停留时间,同时记录了气泡在真空室内的存在形式.气泡在真空室的存在形式的主要影响因素为提升气体流量,研究发现了气泡从规则独立的大气泡经历聚合长大,碰撞破碎成小气泡,最后变成小气泡和不规则大气泡共存的现象.液面高度达到80 mm之后,气泡在真空室内的停留时间达到一个平衡值,不再随真空室液面高度的增加而发生改变.当提升气体量达3000 L·min-1,气泡停留时间减小趋势弱,对应3000 L·min-1情况下,真空室内气泡开始聚合长大.研究认为对于300 t RH的真空室液面高度应为80 mm,提升气体量应在3500 L·min-1左右,优化后,脱碳时间由原工艺的21.4 min缩短至现工艺的17.5 min.      

含锰钢RH真空过程锰的迁移行为

Ruhrstahl Heraeus（RH）精炼炉是重要的二次精炼装备,但在真空处理过程中会遇到钢液易挥发合金元素的损失量大的问题,且造成钢液真空喷溅的结瘤及对后续钢液的二次氧化。针对含锰钢RH真空处理过程锰的气化导致的元素损失及真空喷溅等问题,跟踪和研究了120 t RH不同真空处理模式下钢液中Mn元素的变化规律及迁移行为。分析了锰元素损失与其挥发和真空喷溅的关系,并在RH真空室内壁不同位置结瘤物的解剖实验中得到验证。研究表明,钢液中Mn元素在RH真空过程中存在着明显损失,真空前期损失量最大;RH真空室内壁结瘤物中锰氧化物的质量分数整体占比高达14%～70%;热力学计算结果显示:温度、钢中Mn的含量以及真空度对Mn的挥发行为均有着很大的影响,是真空过程锰迁移的关键影响因素。通过改进真空压降模式,采用步进式抽真空,元素锰的损失由原先的2×10?4降低至1×10?4,结果对现场生产具有很强的指导意义,通过改进真空压降模式可以有效的抑制钢液的喷溅和挥发,进而减少合金元素锰的损失。      

马钢CSP流程RH精炼钢水温度预测模型

基于冶金机理和传热学计算,分析研究了RH精炼过程中脱碳、吹氧加铝、脱氧、合金化、喷粉、真空室状态以及钢包等级等各类因素对钢水温度的影响。结合现场实际生产数据,建立了RH精炼钢水温度预测模型,经过对实际生产跟踪验证表明,模型预测的钢水终点温度与实测值偏差在±5 ℃以内的命中率为87.42%,偏差在±8 ℃以内的命中率为100%。     

RH强制脱碳与自然脱碳工艺生产IF钢精炼效果分析

西昌钢钒厂由于转炉热量不足而以转炉—LF精炼—RH精炼—连铸工艺生产IF钢,为探究RH强制脱碳与自然脱碳工艺生产IF钢精炼效果,采用生产数据统计、氧氮分析、夹杂物自动扫描、扫描电镜和能谱分析等手段,对不同脱碳工艺对顶渣氧化性以及钢的洁净度影响进行了详细研究。结果表明:（1）与自然脱碳工艺炉次相比,采用强制脱碳工艺的炉次在转炉结束与RH进站钢中的平均[O]含量更低;（2）两种工艺脱碳结束钢中的[O]含量基本在同一水平;（3）强制脱碳工艺的炉次在RH结束时渣中平均T.Fe的质量分数降低了1.3%。在能满足RH脱碳效果的前提下,尽量提高转炉终点钢液碳含量、降低钢液氧含量,后续在RH精炼时采用强制吹氧脱碳工艺,适当增大吹氧量来弥补钢中氧,可显著降低IF钢顶渣氧化性。自然脱碳工艺与强制脱碳工艺控制热轧板T.O含量均比较理想;与自然脱碳工艺相比,强制脱碳工艺可有效降低IF钢[N]含量,这与强制脱碳工艺真空室内碳氧反应更剧烈所导致的CO气泡更多和气液反应面积更大有关。脱碳工艺对IF钢热轧板中夹杂物类型、尺寸及数量没有明显影响,夹杂物主要由Al₂O₃夹杂、Al₂O₃–TiO_x夹杂与其他类夹杂物组成,以夹杂物的等效圆直径表示夹杂物尺寸,以上三类夹杂物平均尺寸分别为4.5、4.4和6.5 μm,且钢中尺寸在8 μm以下的夹杂物数量占比高于75%。在RH精炼过程中,尽量降低RH脱碳结束钢中[O]含量,有利于提高钢液洁净度。      

RH浸渍管内径对钢液精炼与洁净度的影响

使用不同内径尺寸的RH浸渍管进行工业生产试验,试验结果表明:浸渍管内径越大,钢液脱碳、脱氢速率越高、浸渍管耐材侵蚀率降低、洁净度提高.浸渍管内径由450 mm扩大到510 mm,钢液初始碳质量分数0.05％ 经过RH深脱碳至0.01％ 以下,时间缩短了8 min,效率提高了61.5％;经过真空循环脱气后,钢液氢质量分数...     

LF钢包吹氩过程的数值模拟

根据对LF钢包吹氩过程的模拟结果,得出最佳喷吹流量,这样可以提高吹氩气体对钢液的搅拌效率、加快温度的均匀化,同时也有利杂物的去除.通过对气泡脱碳的研究,能准确控制钢中碳含量、提高钢水品质、优化钢的质量.     

超低碳钢RH冶炼脱碳过程的数学模型

在充分考虑RH平衡碳氧浓度的前提下,建立脱碳反应数学模型.以210 t超低碳钢RH冶炼工艺为背景,详细给出数学模型的建立原则与过程.将模拟结果与实际测量数据进行对比发现,数学模型与实际测量数据有很好的吻合度.碳元素在钢液内存在一定的不均匀性,真空室自由液面下降管上方碳元素质量分数最小,钢渣界面处上升管右侧碳元素质量分数最大,循环20 min后,二者相差0.0025%左右.      

太钢VOD冶炼超纯铁素体不锈钢的工艺技术进步

阐述了超纯铁素体不锈钢的超低碳氮的特点及其熔体降碳去氮困难的原因,利用真空降碳去氮的理论结合这方面的研究成果分析和讨论了影响VOD脱碳脱氮的影响因素,并利用VOD现场冶炼的具体数据进行了这些因素的统计分析,在此基础上提出了提高真空度、加强底吹氩搅拌强度、提高入炉钢液温度、提高人炉碳含量和降低人炉氮含量、增加VOD吹氧脱碳时的供氧量、高真空吹氩纯沸腾工艺、选用无碳、或低碳还原料等工艺技术措施,最后介绍了太钢这几年在VOD冶炼超纯铁素体不锈钢采取上述措施后所取得的效果。     

Bubble Entrapment on Solidified Shell caused by Unsteady Steel Flow in Mold

The molten steel flow in the continuous casting mold and entrapment of inclusions and bubbles on the inner surface of the solidified shell are examined to clarify the mechanism of internal defects in steel products. Defects on steel sheets are caused by bubbles and inclusions entrapped on the solidified shell during casting. It was found that bubbles penetrate deeply due to an unbalanced time‐dependent flow. This phenomenon can be explained by the Large Eddy Simulation model, which can predict the time‐dependent flow. The number of inclusions increases as the bubble diameter and the distance of the position of entrapment from the top free surface increase. This indicates that bubbles collect inclusions while traveling in the molten steel in the continuous caster. A simple mathematical model is presented to explain the mechanism by which inclusions become attached to bubbles.     

超低碳钢RH混合喷吹Ar-CO2冶金反应特性

 钢铁生产过程CO₂的资源化利用对中国“碳达峰,碳中和”目标的实现起着重要作用。氩气驱动的RH(ruhrstahl-heraeus)真空装置是超低碳钢精炼的关键设备,利用高真空下钢水循环流动可有效脱碳、脱气和去除夹杂物。由于真空条件下CO₂可直接与钢水中碳反应生成CO,在实现脱碳的同时可促进熔池搅拌。因此,尝试将Ar-CO₂混合气体作为提升气体引入超低碳钢RH脱碳过程。首先,针对CO₂在RH脱碳条件下的冶金反应行为,通过热力学理论分析了不同压力下Fe-C-O熔体与Ar-CO₂的反应特性。其次,搭建了Ar-CO₂混合气体作为RH提升气体的工业试验平台,通过工业性试验研究了超低碳钢RH脱碳过程混合喷吹Ar-CO₂对钢水脱碳、脱氮和温降的影响。Fe-C-O熔体与Ar-CO₂反应热力学表明,在低于100 kPa和超低碳条件下,Ar-CO₂混合气体中的CO₂仍可能与钢水中碳反应,从而促进RH脱碳和脱气。工业性试验表明,喷吹100% CO₂、50% Ar+50% CO₂和100% Ar炉次出站平均碳质量分数分别为0.001 50%、0.001 57%和0.001 19%,因而混合喷吹Ar-CO₂并不会显著影响RH脱碳效率。同时,由于CO₂与钢水中碳反应十分有限,与喷吹100% Ar相比,喷吹100% CO₂和50% Ar+50% CO₂对RH脱氮效率和钢水温降没有明显影响。因此,超低碳钢RH脱碳时,完全可采用CO₂取代部分或全部氩气作为提升气体,尽管无法提高精炼效率,但仍具有显著的经济价值和环保优势。     

RH碳酸盐分解CO2脱碳工艺

 提出RH碳酸盐分解CO2脱碳工艺。通过从RH上升管喷吹碳酸钙粉剂实现钢水脱碳和净化钢液的目的。分析RH碳酸盐分解CO2的脱碳机理,并进行工业试验,考察RH碳酸盐分解CO2脱碳工艺对钢水洁净度的影响。结果表明,采用RH碳酸盐分解CO2脱碳工艺缩短RH精炼处理时间3 min,吨钢成本降低3～5元。铸坯的平均[w(T[O])]可达0.001 0%以下,显著提高钢水的洁净度。     

Thermal analysis of walls in a new-type billet caster tundish with a vacuum shell

To reduce thermal loss from molten steel in a tundish during continuous casting production, a new tundish fabricated by welding radiation-proof steel plates onto the steel plates of the exterior walls of a billet caster tundish was proposed.This new tundish was used to investigate the effect of pressures inside the vacuum chamber on the uniformity of the temperature of molten steel and the thermal conditions of the vacuum layer.The results show that the conversion radiation coefficient is not sensitive to pressure and its value at high temperatures is merely 1.5 times greater than that at low temperatures.Pressure is the key factor af-fecting additional factor of conversion convection.This factor is more than 100 times greater at 105 Pa than at 102 Pa, and the temperature at inner points at 102 Pa is, on average, 4 K higher than that at 105 Pa. Meanwhile, the local temperature difference of the inlet at 102 Pa is 1 K higher than that at 105 Pa.Thus, the proposed vacuum billet caster tundish can achieve low superheat teeming of steel because of the ther-mal preservation capability of the vacuum, which helps to reduce the tapping temperature and improve the uniformity of the temperature of steel.