Preliminary Investigation of Mathematical Modeling of Stainless Steelmaking in an AOD Converter: Mathematical Model of the Process

Mathematical modeling of stainless steelmaking in an AOD (argon‐oxygen decarburisation) converter with side and top combined blowing has been preliminarily investigated. The actual situations of the side and top combined blowing AOD process were analysed. A mathematical model for the whole refining process of stainless steel has been proposed and developed. The model is based on the assumption that one part of the oxygen blown through a top lance reacts with CO escaping from the bath, another part of the oxygen oxidizes the elements in the molten steel droplets splashed by the oxygen jet, and the remaining oxygen penetrates and dissolves into the molten steel through the pit stroked by the jet. All the oxygen entering into the bath oxidizes C, Cr, Si, and Mn dissolved in the steel and also the Fe of the steel melt, but the FeO generated is also an oxidant of C, Cr, Si, and Mn in the steel. During the process, all possible oxidation‐reduction reactions occur simultaneously and reach their equilibria, respectively their combined equilibrium, in competition at the liquid/bubble and liquid/slag interfaces. In the simple side blowing after the top blowing operation is finished, the possible reactions take place simultaneously and reach a combined equilibrium in competition at the liquid/bubble interfaces. The overall decarburization rate in the refining process is the sum of the contributions of both the top and side blowing processes. It is also assumed that at high carbon concentrations, the oxidation rates of elements are mainly dependent upon the supplied oxygen rate, and at low carbon contents, the rate of decarburisation is primarily related to the mass transfer of carbon from the molten steel bulk to the interface. It is further assumed that the non‐reacting oxygen blown into the bath does not accumulate in the steel and will escape from the bath and react with CO in the atmosphere above the bath. The study presents calculations of the refining rate and the mass and heat balances of the system for the whole process. Additionally, the influences of the operating factors, including addition of slag materials, scrap, and alloy agents, the non‐isothermal conditions, the changes in the amounts of metal and slag during the whole refining process, and others have all been considered.     

Effects of BOF top blowing and bottom stirring conditions on suppressing excessive oxidation

Abstract

The effects of top blowing and bottom stirring conditions during steelmaking in a 6 t basic oxygen furnace (BOF) were investigated in studies with the aim of suppressing excessive oxidation. With low oxygen feed rate and high stirring energy, the apparent partial pressure of CO P′_CO was calculated from the equilibrium of carbon and oxygen in molten steel as being <1 atm. The relationship between top blowing/bottom stirring conditions and mass transfer at the slag/metal interface was analysed. It is proposed that mass transfer at the hot spot is significantly affected by the reaching rate of oxygen to the steel bath and bottom stirring. Mass transfer at the slag/metal interface, outside the hot spot, is sufficient to allow equilibrium to be attained in combined blowing BOF processes. Thus, the oxygen that is not consumed for decarburisation is distributed between steel and slag, i.e. deoxidation from steel to slag takes place, which makes it possible to obtain P′_CO <1 atm under atmospheric conditions. The decarburisation model developed based on the analysis reproduces the suppression of excessive oxidation under a decreased, top blown oxygen feed rate and is in good agreement with results from both 6 t BOF experiments and 350 t commercial BOF operation.     

Mathematical modelling of decarburisation and degassing during vacuum circulation refining process of molten steel: application of the model and results

The mathematical model for decarburisation and degassing in the vacuum circulation refining process of molten steel, proposed and presented earlier, has been applied to the refining process of molten steel in a multifunction RH degasser of 90 t capacity. The decarburisation and degassing processes in the degasser under the RH and RH‐KTB operating conditions have been modelled and analysed using this model. It was demonstrated that for the RH and RH‐KTB refining processes, the results predicted by the model are in good agreement with some plant data. The mean contributions of the three refining sites in six circulation cycles to decarburisation are 10.5 – 11.6, 37.4 – 38.0 and 50.5 – 52.1 % of the overall amount of decarburisation, respectively. The KTB operation can markedly accelerate the decarburisation of molten steel. Using the top blowing oxygen of 6 min with the flow rate of (600 ‐ 1000) m³(STP)/h, the initial carbon mass content of the liquid steel for the RH refining process may be increased to (550 ‐ 700) · 10‐⁴ from 400 · 10‐⁴ %. And the treatment time needed for reducing the carbon mass content in the steel to a level of ≤ 20 · 10‐⁴ % may be shortened over 3 ‐ 4 min. The effectiveness of decarburisation and degassing cannot be obviously improved by increasing the lifting argon blow rate to 900 from 600 I(STP)/min under the operating modes examined in the present work.     

优化炼钢模型控制超低碳钢转炉冶炼终点

超低碳钢终点氧含量直接关系到后续工艺处理及最终产品质量。包钢金属制造公司对转炉冶炼过程底吹、副枪模型系统计算参数进行了优化,提高了冶炼过程底吹供气强度,加强底吹对熔池搅拌,同时针对超低碳钢制定了底吹供气模式。结果表明,采取以上工艺,能够降低终点氧含量,提高超低碳钢终点碳含量、温度、氧含量命中率,为后续工序提供较好的钢水条件。     

120 t转炉底吹CO2工艺研究及应用

介绍了某钢厂采用底吹CO2工艺,转炉冶炼CSP中低碳钢过程的变化,探究底吹CO2的工艺优势,为后续工艺优化提供借鉴.通过在120 t顶底复吹转炉进行底吹CO2工艺试验研究,分析了底吹CO2对钢水成分、炉渣成分、氧气消耗、钢中氮氧含量的影响.试验结果表明:底吹CO2工艺替代常规工艺切实可行,且有明显的工艺优势.底吹0.9...     

攀钢半钢炼钢技术进步及效果

介绍了攀钢在半钢炼钢工艺的技术进步及其效果，通过采用铁水预处理，使用活性石灰造渣，改进造渣工艺和终点控制制度，实施溅渣护炉等措施，有效地控制了终点钢、渣氧化性，缩短了冶炼周期，提高了生产率，提高了炉龄，提高了钢质量。     

EAF+LF+VOD/VHD冶炼超级双相不锈钢工艺实践

介绍了抚钢超级双相不锈钢冶炼工艺流程,进行了VOD炉真空吹氧去碳、包底吹氮、二次造渣及喂线处理生产实践。研究表明,通过设定合理的吹氧、吹氮工艺,实现了低碳含量、准确氮含量的控制。通过在还原过程中调整合适的炉渣碱度,对钢液进行喂线处理,强化脱硫脱氧,从而改性夹杂物形貌,以确保钢液精准的化学成分及良好的纯净度控制,为热加工创造有利条件。     

RH精炼过程中吹氧量对IF钢洁净度的影响

无间隙原子钢（IF钢）主要用于汽车、家电等行业,除需要极低的C、N含量外,对最终产品的表面质量也有严格要求。钢中O含量和夹杂物对产品的表面质量影响很大。快速降低钢中C含量、同时保证钢的高洁净度是非常重要的。为此,通过在Ruhrstahl Hereaeus（RH）精炼?连铸过程密集取样,采用ASPEX扫描电镜详细研究了RH吹氧强制脱碳工艺下吹氧量对IF钢洁净度的影响。结果表明,本实验条件下,吹氧量对精炼?连铸过程中夹杂物的类型和形貌没有影响。吹氧量对RH精炼前期（加Al后4 min内）钢液洁净度影响较大,而对后期生产过程中钢液的洁净度影响不大;精炼前期,吹氧量高,钢液中总氧（T.O）含量和夹杂物的量增加。簇群状夹杂物主要出现在RH破空之前,真空精炼结束后钢液中很难发现簇群状夹杂物。中间包钢液洁净度与RH吹氧量相关性不大,而与加Al脱氧前钢液中O含量相关性很大,加Al脱氧前钢液中O含量高,中间包钢液洁净度差;为提高中间包钢液的洁净度,应尽量减少加Al脱氧前钢液中的O含量。随着生产的进行,钢液中T.O含量、夹杂物的量呈下降趋势,洁净度逐渐提高。      

CO2顶吹比例对转炉终点控制的影响

结合CO₂的高温反应特性,针对性地制定了CO₂冶炼工艺,并对转炉顶吹CO₂比例对终点磷、氮和碳氧浓度积的影响进行了工业试验研究。结果表明:随着转炉冶炼前中期CO₂顶吹比例由4.84%逐渐提高到9.68%,转炉终点磷的质量分数先下降后基本不变,氮的质量分数逐渐下降,碳氧浓度积与渣中TFe变化趋势基本相同,均为先降低后增加,对于不同指标最佳顶吹CO₂比例不同。试验转炉终点磷、氮的质量分数、碳氧浓度积与渣中TFe均下降,下降比例最高分别为20.4%、34.3%、12.92%和8.89%。      

高热装铁水比冶炼工艺的优化

 针对电弧炉炼钢过程中石灰消耗较高、炉渣中FeO含量过高的问题,研究了温度、炉渣成分、渣量、流渣时机对脱磷的影响以及终点碳含量、炉渣的碱度、吹氧强度对终点渣中FeO含量的影响,并对吹氧制度、造渣制度进行了优化。工业应用表明：石灰的消耗从每吨铁34. 3kg降到25. 2kg,氧气的消耗从每吨铁48. 2m3降到42. 5m3,终渣中w(FeO)从33. 4%降到25. 1%,终点w［C］从0. 07%提高到0. 15%。     

全冷装平炉异位双流双枪顶吹氧炼钢工艺试验

介绍１００ｔ特钢冷装平炉异位双流双枪顶吹氧炼钢工艺。此工艺较单流单枪顶吹氧工艺可进一步缩短冶炼时间，降低消耗，提高炉顶，炉底寿命和配碳合格率，减少化学成分波动，可作为特钢平炉挖潜改造的有效途径。     

VOD冶炼超纯铁素体不锈钢脱碳工艺的研究

针对不锈钢冶炼特点,通过脱碳热力学和动力学分析,研究了VOD精炼工艺参数对超纯铁素体不锈钢脱碳速度和终点碳含量的影响,并进行了大量工业生产试验.结果表明,提高冶炼温度、增加吹氧流量和吹氩流量、降低氧枪的供氧压力和枪位有利于提高脱碳速度,获得更低的终点碳含量.     

节能降碳的蓄热式加热炉烟气反吹关键技术

摘要：蓄热式加热工艺是大型钢铁企业轧钢工序普遍采用的加热技术,但该工艺高频率换向蓄热燃烧导致公共管道内的燃气交替排入大气造成环境污染和能源浪费,使其成为钢铁生产流程中少有未进行污染物治理的生产工序。基于消除蓄热式加热炉热工制度缺陷,系统介绍了蓄热式加热炉烟气反吹扫技术及与之匹配的加热炉烟气反吹安全联锁与防爆技术、烟气反吹工艺设计与时序调控技术。该成果应用于某钢铁企业蓄热式加热炉（160t/h）建设国内首套换向残留燃气反吹技术示范线,该加热炉燃气放散体积分数由9.0%降低至0.208%,CO放散减排率达92%以上,轧钢燃气耗量节约4.38%。其后承建多家钢铁企业19条蓄热式轧钢加热炉烟气反吹改造工程,均取得较好效果,节能、环保及社会效益显著,同时减少碳氧化物的排放量,助力国家实现双碳目标。     

60 t BOF-LF(VD)-150 mm×150mm连铸生产GCr15轴承钢的工艺实践

济源钢铁公司采用60 t顶底复吹转炉高拉碳操作法,控制转炉终点[C]0.08%～0.20%,出钢过程钢包底吹氩并加铝铁脱氧,LF采用CaO-Al₂O₃-SiO₂高碱度渣精炼,连铸钢水过热度20～30℃,M+F电磁搅拌,全程吹氩保护浇铸,铸坯堆垛缓冷工艺生产150 mm×150 mm GCr15轴承钢铸坯。实践表明,GCr15轴承钢的氧含量为（6.3～11.9）×10^-6,平均氧含量为9×10^-6,连铸坯的低倍组织良好。     

转炉采用热补偿工艺提高终点命中率的研究

根据转炉的生产实践,分析了造成转炉终点后吹的主要原因和危害。研究采用吹炼终点前加入碳质固体提温剂,对转炉进行热补偿,可以减少铁的氧化损失,抑制钢水过氧化,提高终点碳命中率,减少以致消除后吹。转炉采用碳质固体提温剂进行热补偿实现终点控制的方法,收到了良好的效果,可大幅度提高炼钢成品率,降低生产成本。     

现代电弧炉炼钢过程物理化学行为及应用

本文研究了现代电弧炉炼钢过程的冶金物理化学变化。研究表明钢水中铁、磷、碳与氧枪吹入的氧气发生直接氧化反应,而钢水中的溶解氧无氧化能力、渣中氧化铁无脱磷能力;钢水中碳与氧气的反应最为剧烈,可通过调整配碳量与吹氧强度可对其它各反应进行控制。在实际生产熔炼过程中,通过及时加入碳粉、焦炭或石墨块,还原渣中氧化铁,可以提高钢水收得率。冶炼过程化清后,通过强化吹氧至接近终点氧,减缓升温速度,流渣换渣,可以深度脱磷,并有效抑制“回磷”。     

120 t顶底复吹转炉终点碳含量控制对钢水脱磷的影响

研究了120 t转炉在终点钢水平均温度1630℃,平均终渣碱度4.0时,终点[C]（0.029%~0.176%）对终点[P]和磷分配比的影响。34炉次冶炼结果表明,终点出钢磷含量随着碳含量的减小而降低,当碳含量低于0.06%时,有利于实现磷含量低于0.005%出钢;随着终点碳含量的降低,渣钢间的磷分配比增大,炉渣脱磷能力增强;在同等工艺条件下,终点碳含量越低,供氧时间越长,吹氧和碳氧反应对熔池的搅拌作用有利于进一步脱磷。     

电弧炉超音速集束氧枪吹炼的钢水留碳操作实践

建立了70 t电弧炉冶炼中高碳钢的留碳操作的数学模型。按照出钢时钢水碳含量的要求,基于入炉废钢和铁水成分,控制超音速集束氧枪的吹炼参数,合理使用炉门自耗式碳氧枪和采用相应的炉渣碱度,以实现目标留碳操作。0.55%C钢的冶炼实践表明,当热装铁水30%时,电弧炉终点[C]为0.40%～0.65%的炉次≥85%,显著降低了冶炼成本。     

转炉多元喷吹提钒的基础研究

转炉提钒是实现钢-钒分离的关键环节,反应动力学条件弱严重影响转炉提钒效果.基于此,提出转炉多元气体喷吹提钒,通过热力学研究了 CO2与C、V反应的选择性氧化转化温度,根据物理热及化学热两方面分析了多元气体的综合冷却效果,并利用熔池搅拌能量密度量化了多元气体的搅拌能力.研究表明:利用多元气体喷吹提钒是可行的,CO2的物理...     

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.