动态轻压下模型的开发及优化

为确保提高连铸板坯铸坯内部质量,开发了一套完整的轻压下模型,包括凝固传热、二冷水动态控制和辊缝控制模型,并对动态轻压下技术的关键参数进行了优化. 通过射钉实验和铸坯表面温度测量,对该模型进行了校核. 实验结果与模型计算结果较为一致;当拉速变化时,铸坯表面温度可以保证在较小的范围内波动. 采用不同的轻压下参数进行生产试验,并通过铸坯低倍检验和中心偏析分析,对压下量和压下位置进行了优化,得出固相率(fs)0.2～0.5、单位压下量1.2 mm·m-1为本铸机最佳的轻压下参数.     

连铸方坯动态轻压下位置

为准确确定铸坯凝固末端的位置,合理选择压下区域,为实施动态轻压下提供有效技术手段,利用数值模拟方法计算某炼钢厂2#铸机连铸方坯中温度场,用传热模型分析了45#钢在某工艺下的铸坯温度分布图.固相率0.3为轻压下初始点,压下区间总长度为10 m且拉速0.76 m/min时的压下量为0.7 mm/m.     

连铸方坯动态轻压下位置

为准确确定铸坯凝固末端的位置,合理选择压下区域,为实施动态轻压下提供有效技术手段,利用数值模拟方法计算某炼钢厂2#铸机连铸方坯中温度场,用传热模型分析了45#钢在某工艺下的铸坯温度分布图。固相率0.3为轻压下初始点,压下区间总长度为10 m且拉速0.76 m/min时的压下量为0.7 mm/m。     

连铸大方坯轻压下过程的变形行为

首先从理论上描述了轻压下过程铸坯的三维变形行为,并采用有限元法定量分析了轻压下工艺对铸坯变形行为的影响规律.结果表明:铸坯宽展变形和延展变形达到平衡后,随着压下量增加,铸坯延展率随压下量呈直线关系变化.在相同轻压下条件下,随铸坯长宽比和中心未凝固率的增加,铸坯宽展效率和延展效率下降,压下效率增加.     

邯钢二炼钢厂板坯中心偏析的成因及对策

分析了邯钢二炼钢厂板坯中心偏析的成因.阐述了如何解决由其引起的铸坯质量问题,采取了如下措施:要求中间包钢水[S]＜0.015%,[P]＜0.015%;应用PHOENICS软件,优化了浸入式水口参数,在不增加专门的压下设备条件下,通过逐渐缩小二冷夹辊开口度,在铸坯凝固70%部位,加大夹辊加下量,实现了铸坯总压下4.5 mm的轻压下.     

板坯连铸二冷与轻压下动态设定控制系统平台

为提高铸坯质量与生产效率,针对大型板坯连铸机设计开发了二次冷却与轻压下动态设定控制算法及其运行平台;支持动态二次冷却、动态轻压下设定控制、动态仿真、设备与控制算法配置、平台自身监控与诊断等功能.平台采用分布式结构,由输入输出、控制算法、虚拟被控对象、运行平台管理、监控操作等5个子系统组成;子系统独立运行,采用事件驱动,通过实时数据库共享数据.动态仿真子平台实现了频繁变化的浇铸过程的动态模拟,弥补了静态模拟的不足.两年多的在线运行实践表明系统稳定可靠、可用率达99.6％;铸机生产效率与铸坯质量也有了明显提高.     

凝固末端电磁搅拌和轻压下复合技术对大方坯高碳钢偏析和中心缩孔的影响

基于ANSYS软件建立了310mm×360mm断面大方坯连铸过程二维凝固传热数学模型,并采用窄面射钉试验及铸坯表面测温试验对模型的准确性进行了验证.通过模型研究了过热度、拉速和二冷比水量对铸坯中心固相率以及凝固坯壳分布的影响,并结合高碳耐磨球钢BU的高温拉伸试验结果,确定了最佳的拉速以及最优轻压下压下区间要求.通过工业试验对理论模型进行了验证,并分析研究了拉速对采用凝固末端电磁搅拌(F-EMS)以及凝固末端17mm大压下量的轻压下技术生产310mm×360mm断面大方坯高碳耐磨球钢BU铸坯的偏析和中心缩孔的影响.结果表明:采用凝固末端电磁搅拌和轻压下复合技术,通过调整拉速优先满足轻压下压下区间要求,可显著降低中心偏析、V型偏析及中心缩孔,但如果仅达到凝固末端电磁搅拌位置要求时,则铸坯中心质量不会得到明显改善.拉速为0.52m·min-1且轻压下压下区间铸坯中心固相率为0.30~0.75时,偏析和中心缩孔有很大程度的改善,不合理的压下量分配会引起铸坯出现内裂纹以及中心负偏析.     

宽板坯凝固前沿轻压下率模型的研究

结合连铸坯凝固规律及轻压下技术改善铸坯中心偏析的冶金原理,建立宽板坯轻压下率理论模型。根据某厂连铸宽板坯实际生产条件,以传热模型计算的铸坯凝固温度数据作为轻压下率模型计算条件,分析拉速、浇注温度、坯壳凝固收缩特性对铸坯轻压下率的影响规律。结果表明,在相同的拉速和浇注温度条件下,铸坯轻压下率沿拉坯方向的分布总体呈减小趋势;拉速较高时的起始轻压下率小于拉速较低时对应的起始轻压下率;拉速与平均轻压下率呈线性递减关系:拉速每升高0.1m/min,平均轻压下率减小0.015mm/m;浇注温度越低,轻压下区起始轻压下率的值越高;浇注温度对平均轻压下率的影响较小,浇注温度每升高10℃,平均轻压下率仅减小0.002 5mm/m;铸坯外部凝固坯壳的收缩对整个轻压下区平均轻压下率的贡献量为20.4%～22.3%。     

连铸板坯轻压下过程中间裂纹产生机理

针对板坯连铸过程中间裂纹严重的问题,对中间裂纹的形貌、元素偏析等情况进行分析.通过建立有限元模型,对不同压下位置和不同压下量凝固前沿的受力情况进行计算并与临界应力值进行对比.结果表明：C、P、S等元素在晶界处富集只是促使中间裂纹开裂的内因,真正造成铸坯开裂的原因是凝固前沿所承受的拉应力.铸坯通过矫直段时,多处位置的凝固前沿所承受的拉应力超过钢的临界值,导致凝固前沿容易开裂延伸,形成中间裂纹;而弧形段和水平段处凝固前沿所承受的拉应力不超过钢的临界值,无裂纹产生.统计现场大量轻压下的实验结果显示：轻压下避开矫直区进行时,中间裂纹的发生率降低约41.3%.     

下渣检测技术在连铸钢包生产中的应用

钢包下渣检测已成为现代连铸生产和质量控制的重要技术之一,它对防止钢包过量下渣、提高钢水纯净度,提高连铸钢水浇铸收得率、改善大包操作工的劳动强度和工作环境均有明显的效果.     

Formation of internal cracks during soft reduction in rectangular bloom continuous casting

To investigate the formation of internal cracks in GCr15 bearing steels during the soft reduction process in rectangular bloom continuous casting, fully coupled thermomechanical finite element models were developed using the commercial software MSC.MARC, and microstructures and fractographs were also observed. With the finite element models, the contours of temperature, equivalent plastic strain, and equivalent von Mises stress were simulated. It is observed that the fracture surfaces of internal cracks are covered by cleavage or quasi-cleavage facets. The region of internal cracks in the intergranular brittle fracture mode is in the mushy zone between the zero ductility temperature (ZDT) and the zero strength temperature (ZST). The simulated equivalent plastic strain in the crack region is 2.34%-2.45%, which is larger than the critical strain (0.4%-1.5%), and the equivalent von Mises stress is 1.84-5.05 MPa, which is within the range of critical stress (3.9-7.2 MPa), thus resulting in the occurrence of internal cracks. Reducing the soft reduction amount from 3 to 2 mm can lower the stress under the critical value.     

Development and investigation of electroslag continuous casting

The principle and technological design of electroslag continuous casting (ESCC), including bifilar mode, T-shaped mould, and metal level detecting system, are detailed. Remelting was carded out for 1Crl8Ni9Ti stainless steel with ESCC. The surface finish, chemical composition, macroand microstructures, and inclusions of the remelted billets were characterized. ESCC reduces the cost and increases the productivity in comparison to traditional ESR, while achieves comparably excellent products.     

Application of soft reduction technique to continuous-casting billets

Soft reduction technique can decrease the presence of central porosity and centerline segregation, and thus to enhance the internal quality effectively. In order to produce high quality billets, Xinxing Ductile Cast Pipe Group Co. Ltd. of China has installed a set of soft reduction apparatus on No. 1 caster and has achieved a great success. The principle, operating conditions and controlling factors, and the specification of soft reduction for solidifying billets are introduced. In order to make the effectiveness of soft reduction clear, metallurgical evaluation is made. The results indicate that soft reduction can increase equiaxial zone by 3%.     

非均匀冷却下板坯凝固末端形状及机械轻压下时其对中心偏析的影响

In order to study the effect of continuous casting process parameters on the shape of slab solidification end under non-uniform cooling, a solidification model of a continuous-cast slab with non-uniform cooling condition was established with ProCAST software. The model was verified by the results of nail shooting tests and the infrared temperature measurement equipment. Four characteristic parameters were defined to evaluate the uniformity of the shape of slab solidification end. The results showed that the nonuniformity at the beginning and end of solidification, the solidification end length, and the solidification unevenness increased with the rise of casting speed. For each 10°C increase of superheat, the solidification unevenness increased by about 0.022. However, the effect of superheat on the solidification end length can be ignored. The secondary cooling strength showed minimal effect on the nonuniformity at the beginning and end of solidification. With the increase in secondary cooling intensity, the solidification end length decreased, but the solidification unevenness increased. In addition, the central segregation of the slab produced with and without the mechanical soft reduction (MSR) process was investigated. The transverse flow of molten steel with low solid fraction influenced the central segregation morphology under MSR.