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。      

单流板坯连铸中间包内钢液流动特性研究

以八钢30t单流板坯连铸中间包为研究对象,采用物理和数学模拟方法,研究了中间包内钢液停留时间分布,分析了呈双峰形状的停留时间分布曲线反映的钢液流动模式,并采用新的方法计算了包含短路流的钢液流动模式的特征参数,进一步阐述了中间包内钢液流动特性。得出结论:(1)中间包内钢液流动的停留时间分布曲线呈现双峰形状,主要原因是中间包内钢液存在一定程度的短路流(2)中间包底面宽长比是控制中间包内钢液短路流的最主要因素,当中间包底面宽长比为0.30时,中间包内钢液短路流完全消失。     

薄板坯连铸单流中间包流场的数学模拟

采用数值计算的方法模拟单流中间包内钢液流动行为。计算模拟了无控流装置,应用挡渣墙坝,以及导流隔墙时中间包内钢液流动分布、温度场。结果表明：中间包无控流装置易在中间包中下部形成贯穿流,不利于新旧钢液混合以及夹杂物去除;导流隔墙可使钢液充分上扬,夹杂物易为覆盖渣俘获,有利于夹杂物去除;加装控流装置后,湍动能在到达控流装置前加强,有利于小粒径夹杂聚合上浮;而湍动能在经过控流装置后减弱,有利于钢液平稳流入结晶器;导流隔墙与堰坝组合均可使中间包内钢液充分混合,温度均匀,进出口温差减小。     

宣钢矩形坯连铸机中间包数学模拟研究

应用三维湍流流动的数学模型及计算机模拟技术，对宣钢矩形坯连铸机中间包进行了模拟研究。通过研究发现在不加任何挡渣板的情况下，中间包内的钢液流动形成明显的短路流；不利于钢液的混合和夹杂物的上浮。中间包内加设挡渣板能够有效地防止短路流，有利于钢液的混合和夹杂物的去除。     

通道式感应加热中间包的数值模拟

通道式感应加热中间包为精确控制结晶器内钢液的过热度提供了可能,有必要使用ANSYS和CFX软件计算通道式感应加热中间包电磁场、流场及温度场分布来揭示中间包内电磁冶金过程。计算结果表明:通道内的感生电流密度大于注入室和分配室内的感生电流密度;在中间包通道内磁场和电磁力的不均匀分布促使钢液旋转流动,且在通道内钢液出现双漩涡现象;但是感应加热中间包内钢液温度均匀,其中间包水口截面最高温度与最低温度仅差1 K;无感应加热装中间包进出口温降可达到7 K,采用感应加热技术能够使中间包温降得到补偿。     

中间包钢液非等温现象的水模型研究

钢液的非等温现象对中间包内流体流动和传热有着重要的影响。笔者用热态水模型研究了中间包内钢液的流动规律。结果表明：温度变化导致钢液的密度不均匀,使自然对流影响钢液流动;还给出了不同温差、不同控流装置下中间包内钢液温度的分布,并讨论了在不同条件下自然对流对钢液流动的影响。     

ASF方坯八流中间包内钢液流场的模拟研究

以某钢厂的八流连铸中间包为研究对象,采用数值模拟方法对不同控流结构中间包内钢液流场进行了研究,并通过水模型实验和工业生产进行验证。模拟结果表明:ASF中间包内的挡墙和湍流器能够明显改善钢液的流动状态和温度分布,加上双坝后效果更佳,钢液的流动存在4个环流区,不仅增加了钢液的混合程度,而且中间包内钢液的温度分布更均匀且低温区较少。水模试验表明在空包中加入湍流器和挡墙能明显改善各流流动特性的一致性,且在其基础上加入双坝能进一步改善钢液的流动特性,与数值模拟结果一致,此外,工业生产也完全达到预期效果。     

酒钢方坯中间包冶金性能模拟评价

以相似原理为基础,用水模拟钢液研究中间包内的钢水流动特征,通过测定模型中间包内液体的停留时间分布曲线(RTD),计算其平均停留时间及死区、活塞区和混合区的体积。     

板坯中间包内钢液流动特性

<正>普遍认为连铸过程中钢液的流动行为严重影响着铸坯质量。中间包作为连接钢包和结晶器的分配器,可调节钢水的流动形态。钢包射流在中间包内引起钢液的湍流流动、旋涡流动和回流等现象,影响钢中夹杂物上浮被渣吸附去除的效果。北京科技大学学者通过开展中间包控流装置布置的正交试验,研究了反应器结构对钢水流动行为的影响。着重探讨了不同尺寸中间包的控流装置布置规律及其对钢液流动行为和夹杂物去除的影响,定     

非等温双流连铸中间包内钢液的流动与传热特征

对实际非等温双流连铸中间包内钢液的流动和传动行为进行了数值模拟研究,并实施了现场实测温度,考察了有／无流动控制情况下,非等温中间包内钢液的流动与温度分布特征,对中间包控流装置的设计提出了新观点。     

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 dimension and migration behavior of bubble under annular argon blowing at tundish upper nozzle

The water model experiments were carried out to study the bubble morphology in the tundish and mold with the process of annular argon blowing at tundish upper nozzle. The effects of the position of gas permeable brick, the casting speed and the argon flow rate on the bubble size distribution, the bubble migration behavior and the flow behavior of liquid steel near the liquid level in tundish were further investigated, coupled with the numerical simulation. The results show that with the process of annular argon blowing at tundish upper nozzle, a frustum cone shaped bubble plume can be formed around the stopper rod. The concentration of argon bubbles gradually decreases outward along the radial direction of the stopper rod. Owing to the wall attached effect, the bubble plumes float upward along the stopper rod, which can increase the collision probability between bubbles and the velocity of bubble plumes, causing a larger impact strength on the liquid level in tundish. In addition, a part of small bubbles are wrapped into the nozzle and the mold due to the drag force of liquid steel. With increasing argon flow rate, the number of bubbles in annular bubble plumes and the vertical velocity of liquid steel near the liquid level in tundish increase significantly. With increasing casting speed, the width and the bubble number of annular bubble plumes gradually decrease, leading to a decrease of the vertical velocity of liquid steel near the liquid level in tundish. Increasing the distance between the annular gas permeable brick and the center of tundish upper nozzle, the dispersion of bubbles and the width of bubble plumes increase, and the impact strength of bubbles acting on the liquid level in tundish becomes weaker. As the argon flow rate and the casting speed increase, and the distance between the gas permeable brick and the center of tundish upper nozzle decreases, the gas volume and bubble size in the mold increase. Under the experimental conditions, when the inner and outer diameters of the annular gas permeable brick are 110mm and 140mm, respectively, and the casting speed is 1.2m/min, the appropriate argon flow rate is 4L/min.     

中间包上水口环形吹氩下气泡大小和迁移行为研究

摘要：通过水模型实验研究了上水口环形吹氩工艺下中间包和结晶器内气泡形貌,并结合数值模拟分析了透气砖位置、拉坯速度和吹氩量对中间包和结晶器内气泡尺寸、气泡迁移和中间包近液面钢液流动的影响。结果表明：上水口环形吹氩形成以塞棒为中心的圆台状气泡羽流,气泡浓度沿径向向外逐渐减少;附壁效应使得气泡羽流偏向塞棒壁面流动,增大气泡的碰撞聚并概率和近塞棒壁面的羽流上升速度,对中间包液面产生较大冲击作用;同时,部分细小气泡会随钢液进入水口及结晶器内部;增大吹氩量,中间包内环形气泡羽流中气泡数目明显增多,中间包近液面钢液上升速度增大;增大拉坯速度,环形气泡羽流的宽度和气泡数量逐渐减小,近液面速度减小;增大透气环距水口中心距离,中间包内气泡弥散度增大,环形气泡羽流宽度也随之增大,气泡羽流对中间包液面冲击作用减弱;增大吹氩量和拉坯速度、减小透气环距水口中心距离,进入结晶器的气量和气泡尺寸逐渐增大。实验条件下,透气环内外径为110mm/140mm、拉坯速度为1.2m/min时,吹氩量为4L/min较为合适。     

八流一体式中间包的钢液流动特性分析

以单流中间包停留时间分布曲线(RTD曲线)组合模型为基础,充分考虑中间包各流流量对流动特性的影响,提出一个适合多流中间包的RTD曲线分析模型。该模型使中间包各流所对应的短路流、活塞流、混合区及死区的体积分数之和为100%,有效避免了传统组合模型所导致的各流股对应区域的体积分数之和偏大(超过100%)的情况,使之符合客观物理现实。模型选用短路流、活塞流、混合区及死区体积分数的标准差,进行各流流动一致性判断。以此为理论依据,采用水模拟实验,结合正交设计实验方法,确定八流一体式中间包控流装置的最佳组合为:低孔挡墙+低挡坝+盆式湍流抑制器。     

Modeling of Species Transport and Macrosegregation in Heavy Steel Ingots

In the current study, two significant phenomena involved in heavy steel ingot casting, i.e., species transport and macrosegregation, were numerically simulated. First, a ladle–tundish–mold species transport model describing the entire multiple pouring process of heavy steel ingots was proposed. Carbon distribution and variation in both the tundish and the mold of a 292-ton steel ingot were predicted. Results indicate high carbon concentration in the bottom of the mold while low concentration carbon at the top of mold after the pouring process. Such concentration distribution helps in reducing both negative segregation in the bottom of the solidified ingot and positive segregation at the top. Second, a two-phase multiscale macrosegregation model was used to simulate the solidification process of industrial steel ingots. This model takes into account heat transfer, fluid flow, solute transport, and equiaxed grain motion on a system scale, as well as grain nucleation and growth on a microscopic scale. The model was first used to analyze a three-dimensional industry-scale steel ingot as a benchmark. Then, it was applied to study macrosegregation formation in a 53-ton steel ingot. Macrosegregation predicted by the numerical model was presented and compared with experimental measurements. Typical macrosegregation patterns in heavy steel ingots are found to be well reproduced with the two-phase model.     

稀土钢连铸喂丝工艺存在的问题及对策

稀土钢连铸中间包和结晶器喂丝，生成的稀土氧化物使中间包覆盖剂、结晶器保护渣的使用性能发生变化，稀土夹杂物容易导致水口堵塞、结瘤。针对这些问题，建议研究开发稀土钢连铸专用中间包覆盖剂和结晶器保护渣，同时采取适当的措施防止水口结瘤的产生。     

Mathematical modeling of tundish operation and flow control to reduce transition slabs

Minimization of transition slabs in continuous casting operations is critical for optimum quality and productivity. The number of these slabs is closely related to the tundish geometry and operating practice. Therefore, tundish flow and mixing with various tundish configurations and different tundish operating levels are investigated through computer simulation. Residence time distributions and transitional concentration profiles are predicted. Finally, practical operations for a grade change to reduce transition slabs are assessed.     

连铸工序质量控制实践

为了提高铸坯质量,确保铸机的稳定顺行,武钢某炼钢厂通过一系列工艺优化措施,采用了包括中间包自动开浇、结晶器液面自动控制系统优化、结晶器漏钢预报系统优化等措施,取得了良好效果:中间包自动开浇率上升到98%以上,铸坯综合改判率控制在0.2%以下。