Rapid Dissolution of Quicklime into Molten Slag by Internally Formed Gas

In steelmaking process, quicklime is used to produce CaO-based slag. Although rapid dissolution of quicklime is required for high-efficiency refining, it is known that the rate decreases when dicalcium silicate (C₂S) layer forms around the quicklime by reacting with slag. The equation that driving force is the difference of CaO content between in slag and a liquid phase of slag saturated by C₂S has been often used for estimating the dissolution rate of lime, in which this saturated value is thermodynamically determined. The authors, however, revealed that the quicklime used in actual operation showed much faster dissolving rate than that of completely calcined lime that is covered by C₂S layer during dissolution into slag. This was caused by a gas formation due to a thermal decomposition of residual limestone existed in quicklime. In this study, the dissolution rate of quicklime with the gas formation is quantitatively investigated.     

Development of a numerical model simulating the desulphurisation of liquid steel

A comprehensive numerical model is developed simulating the batch process of liquid steel desulphurisation. Special emphasis is placed on the exact figuring of real process engineering conditions. The model includes time dependent intensive parameters such as the aluminium content and the oxygen content of the liquid steel as well as the temporal course of the CaO-, CaS, Al₂O₃-component activities in the refining top slag. Mass transfer coefficients are derived from practical experience. The computations prove the outstanding influence of the stirring intensity on the rate of the refining reaction. Its progress is delayed by the dissolution of the lime charge at the beginning of the stirring treatment. The simulation model can also be applied to optimize the desulphurisation process with respect to stirring time, state of deoxidation and amount of refining slag.     

Dynamic Model of Basic Oxygen Steelmaking Process Based on Multi-zone Reaction Kinetics: Model Derivation and Validation

A multi-zone kinetic model coupled with a dynamic slag generation model was developed for the simulation of hot metal and slag composition during the basic oxygen furnace (BOF) operation. The three reaction zones (i) jet impact zone, (ii) slag–bulk metal zone, (iii) slag–metal–gas emulsion zone were considered for the calculation of overall refining kinetics. In the rate equations, the transient rate parameters were mathematically described as a function of process variables. A micro and macroscopic rate calculation methodology (micro-kinetics and macro-kinetics) were developed to estimate the total refining contributed by the recirculating metal droplets through the slag–metal emulsion zone. The micro-kinetics involves developing the rate equation for individual droplets in the emulsion. The mathematical models for the size distribution of initial droplets, kinetics of simultaneous refining of elements, the residence time in the emulsion, and dynamic interfacial area change were established in the micro-kinetic model. In the macro-kinetics calculation, a droplet generation model was employed and the total amount of refining by emulsion was calculated by summing the refining from the entire population of returning droplets. A dynamic Fe_tO generation model based on oxygen mass balance was developed and coupled with the multi-zone kinetic model. The effect of post-combustion on the evolution of slag and metal composition was investigated. The model was applied to a 200-ton top blowing converter and the simulated value of metal and slag was found to be in good agreement with the measured data. The post-combustion ratio was found to be an important factor in controlling Fe_tO content in the slag and the kinetics of Mn and P in a BOF process.     

沙钢管线钢LF精炼的低成本深脱硫工艺

 根据沙钢对管线钢的生产需求及制造成本的控制,结合LF钢包精炼深脱硫的相关理论,开发了适用于管线钢的深脱硫精炼渣和低成本深脱硫工艺。使用该工艺,可完全不使用CaF2,只需使用石灰、铝脱氧产物和转炉下渣即可完成造渣,减少了石灰的消耗,降低了生产成本。180t LF生产实践表明:该工艺可将管线钢的硫含量稳定控制在10×10-6以下,精炼平均脱硫率高于85%。同时,该精炼渣具有较强的夹杂物吸附能力,精炼终点的非酸溶铝含量为（20~100）×10-6。     

Investigation on the removal efficiency of inclusions in Al-killed liquid steel in different refining processes

Industry trials were carried out to study the removal efficiency of inclusions in Al-killed liquid steel in the processes of BOF–LF–RH–CC and BOF–RH–CC. It was found that the removal efficiency of inclusions has a high dependence on inclusion types. Solid inclusions are more easily to be removed than liquid inclusions. The removal efficiency of solid Al₂O₃ inclusions is higher than that of solid CaO–Al₂O₃–MgO inclusions. As liquid CaO–Al₂O₃–MgO inclusions coexisted with solid CaO–Al₂O₃–MgO inclusions in the liquid steel, the low removal efficiency of inclusions in RH degassing process was found in BOF–LF–RH–CC process. However, high removal efficiency and ultra-low total oxygen (T.O) content were obtained in BOF–RH–CC process because the inclusions were mainly composed of solid Al₂O₃ although initial T.O content before RH degassing was relatively high. This is due to the fact that solid Al₂O₃ tends to form cluster-shaped inclusions which have both a higher contact angle and a lower work of adhesion with steel than calcium aluminate, resulting in easier removal by RH degassing. Therefore, it is proposed to weaken steel–slag reaction and calcium treatment before RH degassing to retain solid Al₂O₃ inclusions in the steel.     

Production of Low-P Steel

Production of low phosphorus steel using the basic oxygen steelmaking process is conventionally achieved by maintaining a highly basic slag. This leads to high flux consumption, generates a large volume of slag and restricts recycling of the slag due to presence of free lime. The environmental impact goes further, since the calcined lime involves depletion of a mineral resource, consumption of fossil fuels and release of CO₂. However, recent studies indicate that adequate dephosphorisation is possible in the BOF even if the slag basicity is reduced from the current practice (3.3–3.6) to a level of 2.7–2.8. Phosphorus partitioning deviates considerably from equilibrium and post stirring of bath helps in lowering bath phosphorus. Induction furnace is widely used to produce structural grade steel. Since lining is usually acidic, effective phosphorus removal is not achieved. But using basic lining reasonably low phosphorus steel could be produced.     

大型转炉优化造渣工艺提高脱磷的效果

 针对转炉冶炼存在的转炉前期化渣速度慢,冶炼终点钢水、炉渣氧化性高,终点磷含量控制不稳定等问题,利用炉渣熔化性测定、热力学平衡计算、炉渣矿相分析的方法研究了260 t转炉造渣、供氧工艺。结果表明,转炉初期渣熔化温度为1 330 ℃,不利于转炉前期化渣;终渣熔化温度为1 200 ℃,不利于转炉后期的炉衬维护;终点钢水磷含量与渣钢间磷平衡值差距较大,说明转炉吹炼终点动力学条件不足;炉渣中游离氧化钙含量较高,有部分未熔化的石灰。通过优化转炉渣料加入顺序和数量,强化转炉终点氧枪枪位控制、底吹搅拌等技术措施,可获得较高的转炉终点脱磷率和渣-钢间磷分配比,使终点渣-钢间磷含量更接近平衡;终点炉渣发育良好,游离氧化钙含量适中。     

洁净石油管坯钢27CrMoNbV的生产实践

攀钢27CrMoNbV钢的流程为采用铁水预处理-120 t顶底复吹转炉-LF-RH-360 mm×450 mm坯连铸工艺,通过铁水预处理深脱硫,转炉双渣法冶炼脱磷,转炉出钢及LF精炼深脱硫、采用（1.6～2.2） CaO/Al₂O₃精炼渣系、RH处理喂Ca-Si线处理、保护浇注等工艺优化,生产的27CrMoNbV钢化学成分稳定,P≤0.010%,S≤0.004%,[H]≤1.5×10^-6,T[O]≤0.0011%,非金属夹杂A、B、C、D、Ds均≤1.0级,完全满足技术要求。     

转炉炼钢少渣冶炼技术的探索实践

介绍转炉少渣冶炼、炉渣热循环利用实践.可分两个阶段,脱碳出钢留渣、冶炼中期脱磷倒渣留渣与脱碳出钢留渣同时进行（留渣＋双渣）.脱碳留渣冶炼,通过出钢后倒渣、调渣过程控制,抑制留渣造成吹炼前期的喷溅.留渣冶炼使吨钢石灰消耗降低28.6％.“留渣＋双渣”试验,控制转炉前期炉渣碱度及全铁,选择合适脱磷渣倒炉点及温度,保证前期渣脱磷率和泡沫化,最终前期脱磷率大于60％,排渣率大于50％.“留渣＋双渣”技术,吨钢石灰消耗降低46.9％.     

120 t RH自然脱碳精炼低碳钢QD08的生产实践

基于生产数据对120 t RH精炼低碳钢QD08(/%:≤0.07C,0.15～0.35Si,0.25～0.45Mn,≤0.035P,≤0.035S)进行了RH碳氧反应的热力学、动力学分析和自然脱碳分析,得出RH精炼自然脱碳的优化工艺。结果表明,BOF终点温度≥1650℃,RH初始温度≥1 600℃,BOF终点[C]0.04%～0.10%,[P]≤0.018%,出钢前加顶浇石灰200 kg,出钢不加合金和脱氧剂,RH真空度4～8 kPa,6～8 min可使钢水[C]≤0.05%。     

120t BOF-LF-VD-CC流程生产磨球钢B2的工艺实践

磨球钢B2（/%:0.75~0.85C,0.70~0.90Mn,≤0.030P,≤0.030S,0.40~0.60Cr,≤0.20Ni,≤0.20Cu,0.010~0.060Al）的生产工艺流程为120t BOF-LF-VD-180mm×220mm/260mm×300mm坯CC。通过转炉枪位及供氧强度控制、转炉留渣量及底吹流量的优化、转炉全铝一次脱氧;LF精炼渣系精炼渣碱度由3.44提高到4.25、控制VD氩气流量,VD后软吹≥15min;连铸使用整体塞棒包、全保护浇注工艺、钢水10~25℃过热度操作、使用磨球钢专用保护渣和结晶器电磁搅拌320A,4Hz末端300A,10Hz,提高了磨球钢铸坯的内部质量,钢材的各项指标满足标准要求。     

转炉冶炼轴承钢GCr15的生产工艺研究

分析了转炉冶炼轴承钢的优势,对转炉轴承钢氧含量、钛含量偏高和精炼工艺存在的问题进行了讨论,认为精确控制转炉吹炼终点,实现高碳低氧出钢、控制出钢下渣量成为转炉冶炼轴承钢的重要环节;在精炼方面,应加强钢包顶渣脱氧、保证一定的钢水[ALs]含量和提高氩气搅拌效果.     

宝钢含锌粉尘用于转炉前期化渣的工艺实践

对宝钢含锌尘泥的厂内循环利用进行了研究，将含锌尘泥用于改善转炉前期造渣的试验表明，促进了石灰溶解，改善了前期化渣，提高了脱硫率，LT压块和矿石的耗量减少。造渣剂加入未引起钢水的明显增硫，对钢水和炉渣成分没有影响。     

无缝管用低硅ST30A1钢LF精炼过程钢水硅含量控制

分析了低硅钢ST30Al（/%:0.06~0.10C,≤0.05Si,0.30~0.45Mn,≤0.015P,≤0.005S,0.025~0.050Al）在LF精炼过程中钢水回磷量、钢水铝含量、精炼渣二元碱度、精炼渣Al₂O₃含量等因素对钢水增硅量的影响,得出转炉下渣量、钢水铝含量、精炼炉渣碱度是影响增硅的主要因素。通过控制转炉下渣、降低原辅料中的硅含量、调整精炼渣中SiO₂、Al₂O₃含量、控制精炼渣二元碱度14,渣中Al₂O₃为27%,控制钢水铝含量0.010%~0.020%,LF钢水增硅量由原0.033%~0.047%降低到0.004%~0.018%,成品钢水硅含量≤0.035%。     

Utilization of Multiphase Fluxes for the Dephosphorization of Hot Metal

Although steelmaking slags have been usually treated and studied as homogeneous liquids, they are actually mixtures of a liquid and solids in practical processes. CaO‐based refining flux that does not contain fluxing agents such as CaF₂ inevitably forms a heterogeneous slag in normal cases, and hence, it is defined as a “multiphase flux.” Efficient utilization of this type of flux would decrease the consumption of resources and the emission of CO₂, and thus, would reduce the load on the environment. Metallurgical studies on multiphase fluxes are limited, however, the physical chemistry and reaction kinetics of the same are important for the development of advanced refining processes. The reaction mechanism of dephosphorization using a multiphase flux at hot metal temperatures was investigated in this study. The reaction of a P₂O₅‐containing slag with solid CaO was studied by immersing a CaO disc in the slag. A CaO‐FeO layer was formed near the interface, and a solid solution of Ca₂SiO₄‐Ca₃P₂O₈ was observed in this layer. The Fe‐P‐Si alloy reacted with calcium ferrites at 1673 K, and the samples were analysed by XMA. The same solid solution (Ca₂SiO₄‐Ca₃P₂O₈) was observed near the slag‐metal interface, which suggests that the phosphorus removed from the metal gets concentrated in the solid phase. The experimental results were reproduced with a kinetic simulation model. The simulation program was also applied to the reaction of the CaO‐FeO droplet in a hot‐metal bath.     

Decomposition,Reduction and Dissolution Mechanism of Calcium Sulfate in Iron Oxide Dust Pellet

Iron oxide dust generated during oxygen blowing in the BOF process contains a high content of iron. This iron oxide dust can be used as a material of iron source in the BOF slag reduction process or as de‐siliconisation flux or dephosphorization flux of hot metal pretreatment. One of the most practical uses of iron oxide dust is recycling as a form of pellets in the BOF considering easy application and the amount that can be recycled. In the process of making iron dust pellets cement is used as a binder that contains a lot of calcium sulfate. This calcium sulfate is reduced and dissolved in the molten metal during refining in the BOF. If the oxygen content in slag and molten steel is high enough, the reduced sulfate cannot be dissolved into molten metal and it can be removed as SO_x gas. The behaviour of calcium sulfate has been studied using of 50kg high frequency induction furnace and industrial‐scale plant tests were carried out at a 300ton BOF. The results show that for low carbon steels the evaporation of decomposed sulfate increases with increasing oxygen content in the slag while for high carbon steels the decomposed sulfate is reduced into the molten metal.     

美国的炼钢技术现状

综合介绍了美国转炉钢厂的铁水脱硫、转炉溅渣护炉的终点控制、出钢控制和钢包渣２、二镒燃烧、钢色精烧等技术,以及电弧炉钢厂的电弧炉吹氧、氧燃加热、泡沫渣操作、废钢预热、直接还原铁和电弧炉粉尘处理技术的现状和特色。     

钢水精炼配渣模型

考虑钢包带渣量和成分的变化,对CaO-SiO2-MgO-Al2O3(-CaF2)精炼渣系建立配渣模型.模型根据是否用铝还原钢包带渣的SiO2,可分两种情况通过化学计量计算达到目标渣成分时精炼渣各成分加入量.     

Importance of Kinetic Models in the Analysis of Steelmaking Reactions

In this paper, examples of the use of a kinetic model in the analysis of a steelmaking process will be discussed. In decarburization by BOF, the relation between C and O contents is different from that obtained by equilibrium calculations. By the use of kinetic models, it was clarified that the O content in the metal is controlled not only by the C content but also by the FeO activity in the slag. In the vacuum degassing process, the partial pressure calculated on the basis of the relation between C and O contents is much higher than the operation pressure. The kinetic model which considers the circulation between the molten steel in the vacuum vessel and that in the ladle is well known; furthermore, various decarburization mechanisms were proposed. Hot metal dephosphorization occurs under non‐equilibrium conditions because the oxygen potential of the slag and that of the hot metal are different. Process analysis is performed by considering the reaction kinetics based on the coupled reaction model. Recently, a new reaction model has been proposed; this model considers the solid slag, liquid slag, and liquid metal phases and the reaction between the solid and liquid slag, in addition to the reaction between the liquid slag and liquid metal.     

Thermodynamic Simulation of the Influence of the Temperature and the Basicity of a Boron-Containing Slag on Steel Desulfurization

The results of thermodynamic simulation of the desulfurization of a medium-carbon steel by slags of the CaO–SiO₂–MgO–Al₂O₃–B₂O₃ system are presented. The HSC Chemistry 6.12 software package is used for the simulation. The thermodynamic simulation is performed for 20 various chemical compositions of slags with various B₂O₃ contents (1–4%)¹ and basicities ((CaO)/(SiO₂) = 2–5). The computations are performed using the Equilibrium Compositions module in the temperature range from 1500 to 1700°C with an increment of 50°C at a gas phase pressure of 0.1 MPa. The main results of the calculations are presented as the dependences of the change in the sulfur content in steel [S] on the temperature, the content of B₂O₃, and the slag basicity. An increase in the temperature of metal desulfurization from 1500 to 1700°C exerts a favorable effect on the sulfur content for the studied range of slag basicities. In particular, the sulfur content in steel decreases from 0.012 to 0.009% when steel is processed with the slag having 3% B₂O₃ and a basicity (CaO)/(SiO₂) = 2. A positive effect of an increase in the slag basicity from 2 to 5 on metal desulfurization is observed: the degree of desulfurization increases from 61.1 to 97.2% at 1600°C and 3% B₂O₃ content in the slag. As the B₂O₃ content in a slag increases from 1 to 4%, its refining properties decrease significantly in the range of basicity not higher than 2. In the range of high slag basicities (3–4), the negative effect of acidic oxide B₂O₃ on the refining properties of the slag decreases, providing low sulfur contents (which do not exceed [S] = 0.003–0.004% at 4% B₂O₃). At a slag basicity of 5, the sulfur content in steel decreases to 0.001%, all other things being equal. The simulation results can be used for the calculation of steel desulfurization processed by slags containing B₂O₃.