双辊铸轧工艺温度场和流场耦合的数值模拟

 双辊铸轧过程中熔池内金属的流动状态及温度分布直接影响着铸轧过程的稳定性与铸带产品的质量。针对实验室双辊铸轧试验的特点,采用三维有限元法模拟了双辊铸轧过程的热流耦合问题,利用热平衡计算、铸轧实验和模拟相结合的反向方法分段建立了凝固过程中凝壳与铸辊之间热传导系数与铸轧速度、熔池位置之间的关系模型,并分析不同工艺条件下熔池内凝固变化的情况。     

双辊薄带连续铸轧熔池内金属流动及传热特性的研究

本文建立了双辊式薄带连续铸轧熔池内二维传热流动数学模型，使用有限元计算方法实现了控制方程及边界条件的数值求解，计算结果揭示了熔池内的流场、凝固温度场的特点和规律。     

双辊铸轧工艺参数对熔池场变量的影响

双辊铸轧过程控制是一个高度复杂的工程问题,熔池流场和温度场的稳定性直接影响着带坯的质量。研究铸轧工艺参数对流场、温度场的影响规律,对于得到厚度均匀的板带具有重要意义。基于立式双辊铸轧工艺构建了1∶1水模型实验平台和标准湍流数学模型,研究了铸轧速度、熔池接触角及浇注温度对熔池流场、液面波动及出口温度的影响。结果表明:在熔池出口附近,由于熔池体积减小而产生液体回流现象,且回流区域面积与铸轧速度近似成正比。铸轧速度越大,出口温度越高,沿板宽方向温差越小。当铸轧速度大于7.2m/min或熔池接触角小于40°时,熔池液面波动过于剧烈,会严重影响板带的质量。     

基于有限元法的布流器水口结构优化研究

为了研究布流器水口结构与铸轧工艺参数的取值这2个关键因素对薄带产品质量的影响,基于有限元分析软件,建立三维铸轧熔池流热耦合模型。布流器水口结构的部分参数通过正交试验的方法进行了优化,并分析了结构参数对熔池的影响。根据优化后的参数,重新建立模型,研究了铸轧工艺参数对熔池温度场的影响规律。结果表明,布流器侧面水口锥角的取值对熔池出口温度差值影响最大,端面水口倾角主要影响自由液面湍动能差,优化后的熔池模型自由液面湍动能以及熔池出口温度分布更加均匀;熔池出口温度与铸轧速度、过热度呈线性关系,从而得出过热度和铸轧速度的合理取值范围,这为实际生产过程提供理论依据。     

双辊铸轧304不锈钢应力场的数值模拟

首次采用ANSYS有限元软件,在Anand模型基础上对304不锈钢双辊铸轧熔池应力场进行模拟,并对不同工艺参数下的应力分布情况进行了研究及工艺优化。结果表明,铸轧熔池中应力较高的部分主要集中在熔池出口处及熔池与轧辊的接触部分,且随着铸轧速度和浇铸温度的提高,出口处整体应力均呈现减小的趋势。优化后的铸轧速度应控制在0.7 m/s以上,浇铸温度应控制在1 520℃以上。     

不锈钢薄带铸轧过程中的流动特性

采用有限元法模拟了双辊铸轧不锈钢过程的流热耦合问题,分析了铸轧速度对熔池内流场、温度场遥影响以及流场与温度场之间的相互关系,给出了大过程中熔池与铸轧辊之间的热流密度变化趋势及帮轧速度的变化规律,并比较了模拟与试验的结果;给出了薄带表面温度在铸轧过程中的变化及其随铸轧速度变化的趋势。     

双辊薄带钢铸轧过程的流场温度场耦合数值模拟

采用有限元法模拟了双辊铸轧不锈钢过程的流热耦合问题;分析了铸轧速度对熔池内流场,、温度场的影响以及流民温度场与温度场之间的相互影响,给出了凝固过程中熔池与铸轧辊之间的热流密度变化趋势及随铸连的变化规律,并把此模拟的结果与试验的结果相比较,吻合较好;通过熔池内温度场及温度梯度分析了熔池内凝固的发展及其对热流密度变化的影响。此     

双辊板带铸轧凝固过程的数值模拟

根据双辊板带铸轧工艺中金属熔池内的传热特点,建立了笛卡尔坐标系下的传热数学模型,并利用有限差分法对其凝固过程进行了数学求解,从而对双辊板带铸轧凝固过程的传热特点及其影响因素进行总结,并对其加工工艺提出了一些见解,最后将该方法的求解结果和文献中的结果进行了对比。通过本方法的研究,为控制带钢铸轧的凝固过程提供了理论基础。     

双辊薄带铸轧熔池流动规律分析与试验

  依据相似性原理采用1[∶]1比例搭建双辊薄带铸轧水模型试验平台,研究了不同铸速对铸轧熔池流动规律的影响,并建立低雷诺数的湍流数学模型,对熔池内流场和温度场分布规律进行分析。研究结果表明,由于液体的黏性力和轧辊的挤压作用,在熔池芯部区域会产生回流现象。芯部回流可在一定程度上搅动熔池并促使芯部温度降低,有利于促使温度场和溶质场均匀稳定。研究还表明,随着铸轧速度的增加,回流区位置下移且回流区面积增大,回流作用增强。但过大的铸轧速度反而会使液面波动加剧、Kiss点位置过低等问题产生,从而影响产品质量。     

双辊铸轧薄带钢过程铸轧力计算的数学模型

 在双辊铸轧薄带钢过程中,铸轧力的控制是铸轧过程稳定进行和提高薄带质量的关键。为了控制铸轧力,必须建立铸轧力控制数学模型。基于经典轧制理论,采用工程法推导出铸轧过程中熔池区域微元体静力平衡微分方程,根据凝固终点位置即可给出铸轧过程中单位压力分布,进而给出铸轧力计算的数学模型,为铸轧力的在线控制奠定了基础。     

奥炉“死炉”原因、处理方法及预防措施

奥炉熔池熔炼过程主要是将风、氧和天然气通过喷枪输入熔池渣层200~300mm 以搅动熔池迅速完成传热和传质的过程，其三大核心控制参数为熔池温度、冰铜品位和炉渣渣型。奥炉熔池熔炼过程中，受原料波动、炉内锅炉上升烟道掉焦和喷枪枪重脱落等因素影响，会出现熔池温度迅速降低、升温操作不及时、熔池表面大面积结壳，即“死炉”现象。结合生产实践，针对以上“死炉”问题进行原因分析，提出了处理方法及预防措施，旨在为奥炉熔池熔炼操作提供参考。     

双辊铸轧布流过程熔池流场及温度场

双辊铸轧是一种先进的连铸技术,其布流器的布流形式直接影响其产品质量。同时考虑布流器、辊套、熔池、材料非线性和复杂边界条件的基础上,建立了双辊铸轧流固热耦合数值模型,并对熔池流场及温度场的分布规律进行研究。结果表明,熔池在布流器下方和侧面开口附近共存在4处漩涡,且在靠近侧封板一侧存在下凹的高温区。布流器两侧开口宽度对熔池流场及温度场的影响均较大,在侧面和端面开口宽度分别取12和22 mm时熔池Kiss点的位置分布较为理想。对布流器两侧开口宽度同时对应调整,有利于控制熔池Kiss点的位置高度。     

Computational modeling of laser welding of Cu-Ni dissimilar couple

A three-dimensional transient model to solve heat transfer, fluid flow, and species conservation during laser welding of dissimilar metals is presented. The model is based on a control volume formulation with an enthalpy-porosity technique to handle phase change and a mixture model to simulate mixing of molten metals. Weld pool development, solidified weld pool shape, and composition profiles are presented for both stationary as well as continuous laser welding in conduction mode. Salient features of a dissimilar Cu-Ni weld are summarized and thermal transport arguments are employed to successfully explain the observations. It is found that the weld pool shape becomes asymmetric even when the heat source is symmetrically applied on the two metals forming the couple. It is also observed that convection plays an important role in the development of weld pool shape and composition profiles. As the weld pool develops, the side melting first (nickel) is found to experience more convection and better mixing. Results from the case studies of computation are compared with corresponding experimental observations, showing good qualitative agreement between the two.     

预热对激光熔化沉积成形12CrNi2合金钢组织与性能的影响

使用高功率光纤激光器的快速成形系统和电磁感应加热设备,分别在未预热和预热的情况下成形12CrNi2合金钢.通过扫描电镜观察成形件微观组织、维氏硬度计测试不同部位硬度、万能材料试验机测试不同方向的拉伸性能,研究预热对激光熔化沉积12CrNi2合金钢不同方向的组织、硬度、拉伸性能的影响.结果表明:未预热条件下,单道熔池组织为板条马氏体,块状成形件熔池为回火马氏体与贝氏体混合组织,XOZ截面与YOZ截面组织没有明显的组织差别,但YOZ截面整体硬度大于XOZ截面,同时两个截面均出现了大尺寸宏观裂纹缺陷,力学性能差.在预热条件下,熔池由于温度梯度降低发生贝氏体转变,单道熔池呈现性能优异的下贝氏体组织;块状成形件熔池没有发生回火马氏体转变,主要为粒状贝氏体.截面硬度分布较未预热下更为均匀.在拉伸方向及搭接方向均呈现高强度、低塑性特征,抗拉强度可达1189 MPa,屈服强度为951 MPa,伸长率仅为2.8%,性能没有明显的各向异性.预热能够降低熔池中温度梯度,减小热应力,有效控制裂纹缺陷,促进组织均匀化,降低组织、性能的各向异性,提高合金钢成型件力学性能.      

Research on the Advantages of Vortex Smelting Reduction of High-Iron Red Mud (Bauxite Residue)

Russian Journal of Non-Ferrous Metals - In this research, the effects of different stirring speeds on the molten pool flow and the internal flow field of the molten pool were studied by water...     

On heat transfer and liquid mixing in the continuous casting of steel

Calculations are presented for the interaction of heat and fluid flow in the continuous casting of steel. In Part 1 it is shown that for typical superheat conditions the solidification process and the profile of the solidus line are relatively insensitive to the flow pattern in the molten phase. In Part 2 expressions are developed for predicting the dispersion of a tracer added to the molten pool, in the solidified slab. This dispersion is markedly affected by the flow pattern, thus tracer techniques may be used for characterizing the conditions in the molten pool. The effect of mixing on the floatability of inclusions is examined in Part 3. It is found that mixing may appreciably modify the relationship between particle size and floatability.     

Influence of Sulfur Content on Penetration Depth in TIG Welding for High Manganese Stainless Steels

TIG welding of high manganese stainless steels was conducted with different sulfur contents of 5 and 20 ppm. The penetration depth of the welding bead clearly increased even when the sulfur content of the sample was only very slightly increased from 5 to 20 ppm. In situ observation of the surface of the molten pool revealed that the increase in penetration depth of the welding bead could be attributed to an elevation of the average temperature at the center of the molten pool from 2070 to 2200 K due to the generation of an inward fluid flow in the pool. The results of precise measurements of the surface tension of molten high manganese stainless steels using the electromagnetic levitation (EML) technique, thoroughly explained that the inward flow in the molten pool of the sample containing a sulfur content of 20 ppm was induced by Marangoni convection driven by the boomerang shape temperature dependence of the surface tension of the molten sample. The experimental results of the variations in the temperature distribution and the fluid flow direction in the molten pool depending on the sulfur content were reproduced well by a numerical calculation considering the four dominant driving forces of plasma jet, buoyancy, electromagnetic forces, and Marangoni convection, which indicated that the fluid flow direction was dominantly controlled by Marangoni convection.