磁控电渣重熔过程中熔滴-渣池-金属熔池传输特性及凝固组织演变规律研究

ESR(Electro-Slag Remelting) is a key refining and shaping process to manufacture advanced special steel and role material in aviation, nuclear power generation and high speed train field, however, with the increase of ESR ingot's dimension, the refining efficiency will be decreased and the solidification defects frequently appear, which will remarkably influence the performance and the working reliability and safety of the ESR parts, also which is still a serious unsolved problem up to now in ESR industry. In this project, a new idea of magnetically controlled ESR(MC-ESR) process is proposed, by superimposition of multi-type static magnetic field to ESR process, we can strengthen the transferring specialty in melt droplet-molten slag pool-metal melt pool, and influence the nucleation and growth of dendrite crystal in front of solid/liquid interface, by which we can elevate the purifying efficiency and homogenize the solute distribution and solidification structure in ESR ingots. By using physical simulative system and mathematic simulation method, the effect of superimposed static magnetic field on the transitional specialty of the droplets as well the mechanism on the effect to the electric field, magnetic field, electromagnetic force field, temperature field, fluid flow field etc. will be studied, also the transferring specialty in melt droplet-molten slag pool-metal melt pool will be discussed. The driving force of separating the inclusions in ESR process will be revealed based on the theory of electromagnetic hydrodynamics. During ESR process of special steel, the effect of multi-type static magnetic field on cleanliness, shape of metal melt pool, dendrite crystal morphology, carbide size, solute segregation as well the mechanic properties of ingots will be studied carefully. Furthermore, the feasibility of MC ESR-CC process will be investigated. By conducting the study in this project, we will propose a fully new idea to solve the serious problem such as the high inclusions level, severe solidification defects in big size ESR ingots.

电渣重熔是生产高品质特殊钢、航空/核电/高铁用材的关键精炼和成型手段，然而随着锭型尺寸扩大，电渣过程精炼效率下降而凝固缺陷显著增加，严重影响锭材性能和服役安全，一直是亟待解决的行业难题。本项目提出磁控电渣重熔新思路，通过外加多模式静磁场，强化熔滴-渣池-金属熔池中的传输特性，调控固液界面前沿形核和生长过程，来提升精炼效率和均质化电渣锭成分和组织。采用物理模拟和数值模拟手段，从可视化角度考察外加静磁场对熔滴过渡特性以及对电场、磁场、电磁力、温度场、流场的影响机制，研究不同磁场和电场参数下熔滴、渣池、金属熔池中的传输行为。基于电磁流体力学理论，探讨熔滴中非金属夹杂物迁移动力机制。考察多模式静磁场下电渣重熔特殊钢锭洁净度、熔池形貌、枝晶组织、碳化物尺寸、成分偏析以及力学性能的演变规律，探讨磁场调控电渣连铸过程可行性。本项目的研究有望为突破大型电渣锭夹杂超标、凝固缺陷严重的难题提出全新的技术思路。

电渣重熔是生产高品质特殊钢的关键精炼和成型手段，然而随着锭型尺寸扩大，电渣过程精炼效率下降而凝固缺陷显著增加，一直是行业亟待解决的难题。本项目提出磁控电渣重熔新思路，在传统电渣重熔过程中外加多模式静磁场，对电渣重熔精炼和凝固过程进行多级调控。通过电压采集法、Zn-ZnCl2体系物理模拟以及数值模拟研究，发现外加多模式静磁场能够实现自耗电极末端金属熔滴的细化和分散滴落，且在一定范围内外加磁场强度越大，金属熔滴滴落的频率越大，这是由于通过熔滴颈部的较大熔炼电流与外加静磁场耦合在此区域形成振荡洛伦兹力效应，从而改变熔滴滴落的过渡行为。在磁控电渣重熔强化除杂方面，首次提出基于Saffman力的电渣重熔夹杂物去除新机制，并发现外加多模式静磁场后自耗电极末端液膜层变薄、熔滴变细小、熔池变浅平，外加磁场后夹杂物往渣/金界面迁移/去除的动力学条件得以强化，进而实现了电渣重熔过程夹杂物的多阶段强化去除，磁控电渣锭中的夹杂物特别是大尺寸夹杂物（＞20μm）去除效果明显。外加多模式静磁场后熔池变浅平的原因是由于外加磁场与熔炼电流、枝晶间存在的热电流耦合形成复杂洛伦兹力效应，改变熔滴-渣池-熔池金属液/热量传输特征，使得外加静磁场后金属熔池温度场变均匀。此外，由于外加多模式静磁场后熔池变浅（局部冷却时间LST缩短）以及用于液析碳化物异质形核的夹杂物数量变多等因素，实现了特殊钢磁控电渣锭宏观晶粒、微观枝晶、碳化物的三细化，铸坯综合力学性能得到大幅提升，外加磁场后铸态组织的优势也会遗传到电渣锭后续锻造/热处理态。目前项目组以M2高速钢为考察对象已经在相关企业开展了200Kg-1.5T级磁控电渣重熔技术工业试验验证工作，实验室的理论和结果在更大尺寸的工业级实验中得到充分验证，初步效果显著。本项目在JMST、JMPT、MMTA/B、JMRT、MSEA、Science等冶金/材料/材料加工领域权威期刊发表学术论文35篇，申报发明专利13项，培养博士后、博硕士研究生近20人。