高碳铬轴承钢连铸坯V形偏析与碳化物液析机理研究

V-shaped segregation and primary carbide precipitation in this channel in continuously cast strands of high carbon and chromium bearing steel are crucial factors to deteriorate the performance of bearings. However, their evolution mechanisms have not been clarified yet. Therefore, the present work firstly reconstructs the three dimensional dendrite network in the mushy zone of the continuously cast strand with the combination of experimental and numerical methods. Accordingly, a seepage model for the dendrite network is developed to establish the functional relationship between the permeability and the dendrite structure. Secondly, the present work develops a multiphase solidification model of Fe-C-Cr ternary alloy considering liquid, columnar and equiaxed dendrite phases with the volume average method. Coupled with the melt flow and equiaxed dendrite migration induced by thermal and solutal buoyancy and solidification contraction, the model is extended to describe the formation and distribution of V-shaped segregation and reveal the influence mechanisms of continuous casting process conditions. Thirdly, the present work develops a micro-segregation model coupled with primary carbide precipitation with the aid of thermodynamic database Thermo-Calc and carries out in situ observation experiments with high temperature laser scanning confocal microscope. So, thermodynamic characteristics and kinetic behaviors of primary carbide precipitation are revealed. On above bases, V-shaped segregation and primary carbide precipitation models are combined based on immersed boundary method. So, the present work clarifies the precipitation behavior of the primary carbide in V-shaped segregation channel to provide theoretical guidance for optimizing and controlling continuous casting process conditions of high carbon and chromium bearing steel.

高碳铬轴承钢连铸坯V形偏析及其通道内碳化物液析问题，是降低轴承使用性能的关键因素，然而目前它们的演变机制尚未明确。为此，本研究首先重构连铸坯糊状区三维枝晶结构，建立枝晶网络渗流模型，揭示枝晶网络渗透率与枝晶结构之间的关系；其次，在基于体积平均方法的Fe-C-Cr三元多相凝固模型的基础上，耦合热与溶质浮力、凝固收缩诱导的等轴晶迁移和熔体流动现象，建立连铸坯V形偏析模型，阐明V形偏析形成与分布特征，揭示连铸工艺条件的影响规律；然后，基于Thermo-Calc热力学数据库，建立耦合碳化物液析的微观偏析模型，并采用高温激光共聚焦显微镜，开展碳化物液析原位观察实验研究，揭示碳化物液析热力学特征与动力学行为。在此基础上，基于浸入边界法，结合高碳铬轴承钢连铸坯V形偏析与碳化物液析模型，阐明偏析通道内碳化物液析行为，为其连铸工艺优化控制提供理论指导。

本项目围绕GCr15轴承钢微介观凝固特性与碳化物液析问题，重点开展了GCr15轴承钢方坯凝固组织与V形偏析特征、柱状晶向等轴晶转变(CET)机理、枝晶网络渗流特性、连铸凝固传热与组织演变行为规律、碳化物液析行为机制等研究工作。首先，以国内某钢厂240 mm×240 mm轴承钢方坯为研究对象，系统检测了轴承钢方坯的低倍组织、枝晶组织和C、Cr元素偏析特征，揭示了一次和二次枝臂间距随位置和冷却条件的函数关系，明确了轴承钢方坯V形偏析范围、角度等结构参数。其次，采用元胞自动机(CA)法，建立高碳钢二维CET凝固模型，揭示了高碳钢CET过程和类型，定量阐明了温度梯度、冷却速率和初始碳含量对CET位置、新生枝晶数量、尺寸和标准差的影响规律。然后，研发出适合重构连铸坯三维枝晶网络的实验方法，建立了Fe-C合金三维等轴晶与柱状晶网络渗流模型，确定了渗透率随枝臂长度与枝臂间距的变化规律，揭示了冷却速率对等轴晶结构和渗透率的影响规律，预测了轴承钢方坯不同位置处的渗透率。然后，开展了GCr15轴承钢连铸凝固传热与组织演变行为规律研究，探究了过热度、拉速、二冷比水量等工艺参数对轴承钢方坯温度场、坯壳厚度和凝固组织结构的影响规律。在此基础上，采用高温激光共聚焦显微镜(HT-CSLM)模拟了GCr15轴承钢在连铸冷却速率条件下的凝固过程，定量揭示了晶粒形貌特征和生长动力学，并借助蔡司光学显微镜(OM)和电子探针(EPMA)，阐明了冷却速率对凝固组织及C、Cr元素分布的影响规律，进而揭示了碳化物的析出特征，阐明了不同位置处糊状区冷却速率对碳化物尺寸、形貌、特征和析出位置的影响规律，明确了碳化物的析出与控制机制。.项目发表学术论文12篇，其中SCI收录10篇；申请发明专利5项，授权发明专利5项；获得软件著作权1项；培养研究生共7人，已毕业2人。