基于硼和稀土复合处理的超级奥氏体不锈钢凝固和热加工特性的基础研究

Based on the urgent demand of energy conservation and environmental protection, marine engineering, petrochemical and other key areas for super austenitic stainless steels, and the existing key common problems of serious surface cracking and center segregation of the continuous casting billet, poor hot ductility, serious hot rolling cracking and high temperature oxidation of these steels, the optimum design criterion and regulation theory of alloy composition for improving structure stability and corrosion resistance will be established. A new idea of feeding stainless steel strip containing born and rare earth in the continuous casting crystallizer is proposed to relieve center segregation and improve center quality of continuous casting billet. The effect mechanism of boron and rare earth during the solidification process will be revealed. And the technological theory of feeding stainless steel strip will be mastered. The formation mechanism of slab surface cracks will be clarified, and the thermal cracking criterion will be established. The process control method for eliminating surface cracks of slab will be mastered to improve its surface quality. Another new idea of adding boron and rare earth to synergically improve hot ductility and adding rare earth to enhance high temperature oxidation resistance is proposed. The behavior and effect mechanism of boron and rare earth during high temperature homogenization, high temperature oxidation and hot deformation process will be clarified, and the homogenization technology will be optimized, in order to comprehensively improve the hot workability of super austenitic stainless steels. The research results will break through the key common scientific and technical problems of the continuous casting and hot working process of super austenitic stainless steels, and provide technical supports for accelerating their domestic production process and mass stabilization production.

基于节能环保、海洋工程、石油化工等重点领域对超级奥氏体不锈钢的迫切需求，针对该类材料连铸坯表面易开裂、中心偏析严重，高温塑性差、轧制易开裂、高温氧化严重等关键共性问题，建立基于提升材料组织稳定性和耐腐蚀性能的合金成分优化设计准则和调控理论；提出结晶器喂含硼和稀土不锈钢带技术以减轻铸坯中心偏析、提升铸坯心部质量的新理念，并揭示硼和稀土在凝固过程中的作用机制，掌握结晶器喂带工艺理论；明晰铸坯表面裂纹形成机理，建立热裂判据，掌握消除铸坯表面裂纹、提升铸坯表面质量的工艺调控方法；提出加入硼和稀土协同改善热塑性、稀土改善抗高温氧化性能的新思路，揭示硼和稀土在高温均质化、高温氧化和热变形过程中的行为及作用机理，优化高温均质化工艺，综合提升超级奥氏体不锈钢热加工性能。研究成果将突破超级奥氏体不锈钢连铸和热加工过程的关键共性科学与技术问题，为加速国产化进程、推动批量稳定化生产提供技术支撑。

基于高端装备制造业对超级奥氏体不锈钢的迫切需求，针对该类材料连铸坯中心偏析严重、高温塑性差、高温氧化严重等关键共性问题，本项目创新提出以“结晶器喂含硼和稀土不锈钢带”为核心提升凝固质量和热加工性能的新思路。探究了主合金元素及硼和稀土对组织稳定性和耐蚀性的影响，从原子尺度揭示了“硼和稀土抑制铬、钼偏聚，减轻二次相析出，改善钝化膜稳定性”的作用机理，掌握了合金成分优化设计准则。建立了结晶器喂带多场耦合模型和工艺参数调控准则，明晰了喂带过程“鞘壳生成-钢带熔化-钢带熔凝交替-钢带消失”的演变规律，揭示了喂带参数对流场和温度场的影响机制。设计开发了结晶器喂带热模拟装置，实现了连铸坯传热行为和凝固组织的精准模拟，揭示了“稀土夹杂促进枝晶形核，硼和稀土界面偏聚抑制枝晶生长并细化析出”以及“钢带熔化吸热、漂浮枝晶增殖促进钢液形核，细化枝晶并抑制偏析和析出”的凝固组织改善机制，掌握了喂含硼和稀土不锈钢带工艺理论，实现了等轴晶数量倍增，中心析出相含量倍减。构建了连铸坯凝固黏弹塑性三维热/力耦合有限元模型，探究了连铸坯凝固宏观热/力行为，明晰了铸坯表面裂纹形成机理并建立了热裂判据，掌握了消除铸坯表面裂纹的方法。优化了高温均质化工艺，揭示了硼和稀土对组织和成分均匀化的影响机制。阐明了“硼优先偏聚晶界形成高势垒，抑制变形过程铬、钼偏聚和二次相析出”以及“稀土细化晶粒并显著促进动态再结晶”的作用机制，实现了硼和稀土协同改善热塑性，热塑性窗口拓宽40-50℃。明晰了“稀土优先氧化提供形核核心，促进铬表面偏聚和稀土离子氧化物晶界偏聚”的联合抗氧化机制，抗高温氧化性能提升22%-45%。基于上述研究，突破了超级奥氏体不锈钢连铸和热加工过程的关键共性科学与技术问题，丰富发展了硼和稀土微合金化理论及结晶器喂不锈钢带工艺理论。研究成果对解决我国“超级奥氏体不锈钢”短缺的“卡脖子”难题、支撑高端装备制造业快速发展具有重要的战略意义。