连铸机异钢种混合浇铸生产实践

针对宽厚板生产线品种多、小批量合同多,订单复杂的特点,为减少完成合同所用生产浇次,降低生产成本,通过将中包钢水降至极限,实现了不同钢种之间的连续浇铸。该方法的实施使某钢铁厂宽厚板连铸机每个生产浇次的平均连浇炉数由实施前的8.6炉提升至16炉,平均每月减少浇次25个,显著提高了生产连续性,进而降低了耐材消耗及头尾坯的数量,同时优化了宽厚板生产线的产品结构。     

板坯连铸异钢种连浇混浇坯长度及成分变化模型的开发及应用

基于建立的连铸中间包及结晶器内钢液混合过程的物理模型,开发了板坯连铸异钢种连浇过程混浇坯长度及成分变化模型。以某钢厂单流板坯连铸机220 mm×1560 mm断面Q235与Q335Ti钢的混浇过程为研究对象,采用水模型试验结合数值模拟确定模型的关键参数,并通过开展现场试验对混浇坯取样验证模型的准确性。结果证明:混浇坯成分取样与模型预测的成分偏差小于5%,且模型预测的混浇坯长度与人工确定的一致。故采用该模型可跟踪不同混浇工况下中间包内及铸流上钢液的混合行为,准确预测混浇坯的长度以及成分变化规律。采用该模型研究了拉速及中间包内剩余钢液质量对混交坯长度及不同浇注长度铸坯C元素质量分数变化的影响规律。发现当拉速保持不变时,中间包内剩余钢液越多,混浇坯越长;当中间包内剩余钢液质量保持不变时,拉速越大混浇坯越短。相比而言,中间包内剩余钢液质量比拉速对混浇坯长度的影响更大。另外当拉速不变时,随着中间包内剩余钢液质量的增加,C元素质量分数由0.16%变化到0.18%的速率减慢;当中间包内剩余钢液质量不变时,随着拉速的增加,C元素质量分数由0.16%变化到0.18%的速率增加。因此异钢种连浇过程,适当提高拉速以及减少中间包内剩余钢液质量,可有效减少混浇坯长度,成分变化速率降低。      

连铸钢板坯内部裂纹的研究

首先介绍了内部裂纹的定义和分类 ,继而分析了板坯凝固壳横截面变形、应力与内部裂纹之间的一般规律 ,最后指出了现行标准YB T 4 0 0 3- 1991的不足 ,同时也概括了影响内部裂纹的因素。     

Intermixing model of continuous casting during a grade transition

To investigate the composition distribution that develops in continuously cast steel during a grade change, an efficient, accurate, and user-friendly computational model has been developed. The model is fully transient and consists of three submodels, which account for mixing in the tundish, mixing in the liquid core of the strand, and solidification. The first submodel of mixing in the tundish consists of two plug flow zones, two back-mixing boxes, and two dead volumes. The second submodel solves a one-dimensional (1-D) diffusion equation in series with two back-mixing boxes to calculate concentration histories in the strand, and the third submodel transforms these histories into slab compositions. The model was calibrated using both concentration histories measured on tundish water models and calculations from a three-dimensional (3-D) model. It was then verified with several sets of composition measurements along the surface and centerlines of slabs. The model is capable of tracking mixing phenomena for arbitrary tundish filling and casting speed histories. It has been used to compare the effects of different grade change procedures on the amount of intermixed steel, including standard sequence casting, flying tundish change, and insertion of grade separators. Mixing in the strand was found to be very important. Without a grade separator, a flying tundish change had very little benefit on reduced intermixing, for the typical conditions considered.     

Study on the non-uniform slab shrinkage of special steel during slab continuous casting

A full-scale finite-element stress model of a slab and its mould was developed to analyse the non-uniform slab shrinkage of special steel in a vertical caster during slab continuous casting. The stress model was based on the heat transfer model which was validated by comparing the calculated temperature with the measured ones. According to the shrinkage calculation, the single linear taper is not suitable for the continuous casting of this special steel, and the narrow face taper need to be calculated and optimised. It will provide a helpful tool for further improving the casting parameters and operations for special steel.     

中锰耐磨钢连铸板坯分层缺陷分析

基于连铸现场参数收集、相关实验室研究,分析了中锰耐磨钢连铸板坯分层缺陷的发生原因,并基于生产实践,探讨了相关分层缺陷的控制途径。研究表明,热轧板分层缺陷产生的原因一是来料铸坯严重的中心疏松,二是铸坯在二次切割时断面形成的碳化物组织富集造成铸坯不同部位存在较大的温差,产生热应力集中,从而形成(微)裂纹,在轧制时产生开裂。通过采取控制连铸过热度、改善铸坯中心疏松、保证铸坯二次切割温度使铸坯二次切割时产生的热应力弥散分布等措施,可以改善板坯分层缺陷的产生。     

Modeling and control of dynamic soft reduction in continuous slab casting

The centerline segregation in continuous casting steel is known to be formed by the interdendritic enriched liquid flow at the solidification end in strand.At present,several methods,such as thermal soft reduction, electromagnetic stirring and dynamic soft reduction,are available to reduce the center segregation and to improve the internal quality.Although some methods could alleviate center segregation to some extent,they can also give rise to new problems.For instance,thermal soft reduction can lead to surface cracking during casting of some steels and electromagnetic stirring can result in white band.Dynamic soft reduction is an effective technology for the improvement of strand quality in continuous slab casting.In this paper,the key parameters of dynamic soft reduction technology,such as soft reduction region,the total reduction amount,for low carbon steel have been studied based on experimental and theoretical analysis.The soft reduction region was related to the segregation of chemical composition,slab bulging of narrow side and avoiding internal crack of slab.The total reduction amount was composed of natural thermal shrinkage and actual reduction amount depending on critical strain.For low carbon steel with slab dimension of(950 - 1 950) mm×170 mm,the solid fraction range in soft reduction region was recommended from 0.4 to 0.8,the total reduction amount was 2.0 -2.8 mm,and the optimized reduction rate was 0.4 - 1.2 mm/min,respectively.Furthermore,a dynamic soft reduction system in continuous slab casting, Visual Cast-Dynamic,has been developed by multithreading method.It demonstrated that the dynamic soft reduction model in this study was correct with the ability of online control.     

IF钢连铸坯及热轧板夹杂物研究

夹杂物是影响IF钢表面质量的重要因素。对某厂生产的IF钢连铸坯和热轧板取样, 采用光学显微镜、扫描电镜、能谱、大样电解等多种检测分析方法, 分析了夹杂物的形貌、尺寸、数量、分布以及成分等。研究发现, 热轧工艺的轧制作用使连铸坯宽度方向1/4处聚集的夹杂物向边部迁移, 最终造成热轧板边部夹杂物指数最高, 说明夹杂物聚集带在轧制过程中具有遗传性。热轧板中20 μm以下夹杂所占百分比与连铸坯中夹杂相比稍有增大, 50 μm以上夹杂所占百分比稍有降低。热轧工艺的轧制作用将连铸坯中大颗粒氧化铝夹杂挤压变形为热轧板中的长条状, 容易形成表面条状缺陷。夹杂物在连铸坯距内弧侧30 mm处存在聚集现象, 热轧板中距内弧侧0.5 mm处夹杂物指数最高, 这是由于等效应变不同使夹杂物聚集带向表层迁移。IF钢连铸坯和热轧板中主要有4类显微夹杂, 分别为Al₂O₃类、TiN、Al₂O₃-TiO_x和SiO₂类复合夹杂, 且两者中各类夹杂物所占百分比差别不大。      

AH32船板内部裂纹成因分析

以鞍钢股份有限公司AH32船板钢为研究对象,利用Thermo-Calc热力学软件对钢中MnS的析出行为进行了模拟计算;研究了平衡状态下元素含量的变化对MnS析出规律的影响以及AH32船板钢凝固过程特点;利用Quanta-400型扫描电镜对AH32船板内部裂纹进行了微观观察及能谱分析,最终认为共晶反应形成的片状MnS析出物为裂纹产生的主要原因.生产中采取了降低硫含量、二冷弱冷、低拉速、优化电磁搅拌工艺及钙处理等多项措施,取得了明显效果.     

微合金钢薄板坯连铸边角裂纹控制

微合金钢薄板坯连铸过程高发边角部裂纹,致使热轧卷板边部产生翘皮、烂边等质量缺陷,是钢铁行业的共性技术难题。本文立足于某钢厂QStE380TM低碳含铌钛微合金钢薄板坯连铸生产,检测分析了铸坯角部组织金相结构与碳氮化物析出特点、不同冷却与变形速率条件下钢的断面收缩率,并数值仿真研究了不同结构结晶器和二冷区铸坯温度与应力的演变规律。结果表明:微合金钢薄板坯连铸过程存在明显的第三脆性区,且变形速率越大,第三脆性区越显著。传统薄板坯连铸工艺条件下,结晶器的中上部及其出口至液芯压下段的二冷高温区,铸坯角部冷速较低,致使其组织晶界含铌钛微合金碳氮化物呈链状析出。铸坯在液芯压下过程,低塑性角部因受较大变形与应力作用而引发裂纹缺陷。实施沿高度方向有效补偿坯壳凝固收缩的窄面高斯凹型曲面结晶器及其足辊区超强冷工艺,可分别提升铸坯角部冷速至10和20 ℃·s?1以上,从而促使铸坯角部组织碳氮化物弥散析出,并促进铸坯窄面在液芯压下过程金属宽展流动而降低角部压下应力,大幅降低了微合金钢薄板坯边角部裂纹发生率。      

板坯连铸机结晶器内钢液流场的数值模拟

基于流体力学的基本理论,利用商业软件fluent的,κ-ε湍流模型,实现了对结晶器内钢液流场的三维数学模拟.重点分析了浸入式水口的形状、插入深度、水口侧孔倾角以及拉速等工艺参数对结晶器钢液流场的影响.结果表明,对于断面为1280 mm × 180 mm的板坯结晶器,水口插入深度为150 mm,水口倾角为向下15°,拉坯速度为1 m/min时,结晶器内的流场较好.     

Molten steel level stability in continuous casting slab mold under electromagnetic stirring

Fluctuation of molten steel level in continuous casting process is a critical issue. The analytic function for the liquid steel surface stability index( F) of the continuous casting slab mold under the action of electromagnetic stirring was derived. The effects on the F value of the electromagnetic field,casting mold,submerged entry nozzle,and casting speed were observed,and the stability of the process parameters of a practical continuous casting system was evaluated. The main results generated are as follows:①Based on the free flow jet theory,a formula is established for the level stability index of continuous casting slab mold under electromagnetic stirring.②According to the results of calculation,the various parameters in decreasing order of the magnitude of their influence are magnetic flux density,nozzle submersion depth,casting speed,slab width,stirring current frequency,and nozzle side-hole inclination angle.③For practical continuous casting with a slab thickness of 230 mm,the calculated F values are between 3 and 5 for different matches between slab width and casting speed,but the parameter optimization space is much larger for wider slab widths and lower casting speeds.     

Modeling of transient flow phenomena in continuous casting of steel

This paper describes initial efforts to develop and apply 3D finite-difference models to simulate transient flow in the mold. These transient flow phenomena include flow pattern oscillations caused by sudden changes in nozzle inlet conditions and rapid fluctuations in the molten steel⧹flux interface level at the top surface of the mold. The flow model incorporates interactions with other transport phenomena, including turbulence, superheat removal and argon gas bubble injection. Predictions are shown for the oscillatory evolution of the flow pattern from biased steady flow to symmetrical steady flow after a sudden change in inlet conditions. In addition, the predicted turbulent kinetic energy levels at steady state are shown to correlate with measured surface level fluctuations. The effect of processing conditions are consistent with experimental findings. Without argon, the greatest level fluctuations are found near the narrow face, while increased argon moves the maximum towards the center. Fluctuations decrease with deeper submergence and lower casting speed. These transient phenomena are important because they may lead to defects in the final steel product from entrainment of slag, disruption of solidification at the meniscus and non-uniform heat transfer.     

Modeling superheat removal during continuous casting of steel slabs

To investigate superheat dissipation in a continuous slab casting machine, mathematical models have been developed to compute fluid flow velocities, temperature distribution within the liquid pool, heat transfer to the inside of the solidifying shell, and its effect on growth of the shell. Three-dimensional (3-D) velocity and heat-transfer predictions compare reasonably with pre-vious experimental measurements and two-dimensional (2-D) calculations. The results indicate that the maximum heat input to the shell occurs near the impingement point on the narrow face and confirm that most of the superheat is dissipated in or just below the mold. Superheat tem-perature and casting speed have the most important and direct influence on heat flux. The effects of other variables, including mold width, nozzle jet angle, and submergence depth, are also investigated. Calculated heat flux profiles are then input to a one-dimensional (1-D) solidifi-cation model to calculate growth of the shell. Shell thickness profiles down the wide and narrow faces are compared with the predictions of conventional heat conduction models and available measurements.     

Analysis of non-uniform thermal behaviour of special steel during slab continuous casting

A full-scale finite-element model of a slab and its mould was developed to reveal the complex thermal behaviour of special steel in a vertical caster during slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mould. The model was validated by comparing the calculated temperature with the measured ones. The temperature distribution of the slab is not symmetric, reflecting the non-uniform nature of heat transfer and hence the necessity of formulating a full-scale model. It will provide a helpful tool for further improving the casting parameters and operations for special steel.     

Simulation of thermal behavior during peritectic steel solidification in slab continuous casting mold

Thermal behavior of the solidifying shell in continuous casting mold is very important to final steel products.In the present work,one two-dimension transient thermal-mechanical finite element model was developed to simulate the thermal behavior of peritectic steel solidifying in slab continuous casting mold by using the sequential coupling method.In this model,the steel physical properties at high temperature was gotten from the micro-segregation model withδ/γtransformation in mushy zone,and the heat flux was obtained according to the displacement between the surface of solidifying shell and the hot face of mold as solidification contraction,the liquid-solid structure and distribution of mold flux,and the temperature distribution of slab surface and mold hot face,in addition,the rate-dependent elastic-viscoplastic constitutive equation was applied to account for the evolution of shell stress in the mold.With this model,the variation characteristics of surface temperature,heat flux, and growth of the solidifying shell corner,as well as the thickness distribution of the liquid flux,solidified flux,air gap and the corresponding thermal resistance were described.     

薄板坯连铸SPA-H带钢结疤缺陷分析与控制

介绍了武汉钢铁股份有限公司CSP薄板坯连铸连轧生产SPA-H带钢过程中结疤缺陷的特点,对造成结疤缺陷的影响因素进行了分析。在结晶器铜板质量要求、钢中碳和氮含量控制、保护渣理化性能、结晶器冷却等工艺环节进行了工艺优化。在此基础上提出了相应措施,使SPA-H带钢结疤缺陷改判率由2009年的3.67%降为2014年的0.08%。     

韶钢第三炼钢厂板坯连铸生产实践

针对新投产板坯铸机生产中出现的Q345钢粘结漏钢频繁和包晶钢表面纵向裂纹多的状况,分析其原因,并采取相应措施,解决了粘结漏钢问题,提高了铸坯表面质量。