加压对高氮奥氏体不锈钢铸锭氮宏观偏析的影响机理研究

High nitrogen austenitic stainless steels (HNASS) are urgently needed in key fields, such as military equipment, marine engineering, electrical equipment and biomedical fields, etc. However, there are uncomprehensive rule and rudimentary mechanism about the effect of pressure on macrosegregation, during the manufacturing process of HNASS using pressurized metallurgy. In response to that, the change in the mushy zone feature of HNASS with pressure will be analyzed. The effect of dendritic network structure on fluid motion will be investigated. And then the effect mechanism of pressure on fluid motion will be clarified. Combined with the effect of pressure on nucleation, dendrite growth and sedimentation, interaction forces between phases, inclusion movement, and nitrogen dissolution behavior, the pressurized multiphase macrosegregation model will be established. Meanwhile, a new method will be proposed to investigate the influences of multiple factors on macrosegregation. The interaction relation and synergistic effects of multiple factors on nitrogen macrosegregation and pore will be revealed. These research results are beneficial to clarify the influence mechanism of pressure on nitrogen macrosegregation, and further improve the pressurized solidification theory. Based on the above researches, the reasonable matching method of process parameters (solidification pressure, superheat degree and pouring time, etc.) will be mastered. The related achievements will provide theoretical basis for manufacturing HNASS with uniform composition and dense solidification structure using pressurized metallurgy.

基于军事装备、海洋工程、电力装备以及生物医疗等重点领域对高氮奥氏体不锈钢的迫切需求，针对该种材料加压冶金制备过程存在的加压对宏观偏析影响规律研究不全面、机理不明确等诸多不足，本项目拟分析糊状区特性随压力的变化规律，明晰糊状区内枝晶搭桥行为对液相流动的影响规律，阐明压力对枝晶间液相流动的影响机理。结合压力对枝晶形核、生长、沉积以及各相间相互作用力、夹杂物运动和氮溶解过程等的影响规律研究，建立加压多相流宏观偏析模型，创新宏观偏析多重影响因素全耦合的研究方法。明晰多重因素间的联动关系及其对氮宏观偏析和氮气孔形成的协同作用，阐明加压对氮宏观偏析的影响机制，进一步完善加压凝固理论。从而掌握合理匹配凝固压力、过热度以及浇注时间等工艺参数的方法，为加压冶金制备成分均匀、组织致密高氮奥氏体不锈钢的工艺优化提供依据。

基于军事装备、海洋工程、电力装备以及生物医疗等重点领域对高氮奥氏体不锈钢的迫切需求，针对该种材料加压冶金制备过程存在的加压对宏观偏析影响规律研究不全面、机理不明确等诸多不足，本项目分析了疏松随凝固压力的变化规律，结合凝固压力对疏松尺寸、形貌以及类型的影响机理和糊状区内枝晶搭桥行为对液相流动的影响规律，阐明了压力对枝晶间液相流动的影响机理，为揭示加压对高氮奥氏体不锈钢氮宏观偏析的影响机理提供了理论支撑。基于能量、动量和溶质的宏观守恒方程，考虑溶质扩散行为、固液界面热力学平衡关系、枝晶形貌演变、夹杂物运动等，结合压力对铸锭铸型间界面换热、固液相线温度、凝固潜热、比热、密度以及热膨胀系数等重要凝固热力参数的影响，建立了加压下夹杂物分布模型，探究了压力对夹杂物分布的影响规律。同时，结合压力对枝晶形核、生长、沉积、各相间相互作用力、夹杂物运动以及氮气孔的形核、生长和运动的影响规律研究，建立了加压多相流宏观偏析模型，实现了多重影响因素对宏观偏析作用的全耦合研究，阐明了加压对高氮奥氏体不锈钢氮宏观偏析以及氮气孔缺陷的影响机理，进一步完善了加压凝固理论。从而掌握了合理匹配凝固压力、过热度以及浇注时间等工艺参数的方法，为加压冶金制备成分均匀、组织致密高氮奥氏体不锈钢的工艺优化提供了理论依据。