高品质特殊钢加压下熔炼和凝固的基础研究

The dissolution behavior of gas (N2) and volatile elements (Ca, Mg) in molten special steels will be investigated by pressurized metallurgy method, in order to establish the solubility model of nitrogen, calcium, magnesium in molten special steels under pressure. The purification of liquid steel and inclusion modification mechanism will be interpreted under pressurized condition. The calcium, magnesium treatment method which makes the inclusion harmless will be obtained during pressurized metallurgical process. The occurrence state of magnesium and its effect on the elements easily segregated around grain boundary, and the influence of magnesium on the microstructure and properties of special steels will be explored. The mechanism for magnesium to purify and strengthen the grain boundary will be clarified. Furthermore, the control technology of harmful gases (H, O) and volatile elements (Sn etal) will be mastered during pressurized metallurgy process. The influence of the pressure on the solidification phase transition, gap formation between ingot and mold, the cooling rate, the local solidification time, the secondary dendrite space, the formation of shrinkage cavity and porosity in ingot will be studied. The evolution rule of the pressurized solidification microstructure will be revealed, and the pressurized solidification technology which makes the gain refining significantly, reducing the segregation degree and eliminating shrinkage cavity and porosity will be mastered. A low-cost and exact controllable nitrogen alloying method will be put forward by investigation of a micro-arc nitriding method and mechanism during pressurized.electroslagremelting process. The microstructure and properties of the typical special steels obtained under pressurized condition will be investigated deeply. The mechanism on the role of nitrogen and volatile elements in the special steels will be explained. The above results will be helpful to establish and improve pressurized metallurgical theory, and promote the application of pressurized metallurgy method in manufacturing high quality special steels.

本项目通过加压冶金手段研究气体（氮）和易挥发元素（钙、镁）在特殊钢钢液中的溶解行为，建立氮、钙、镁在钢液中的溶解度模型。阐明加压条件下钙、镁净化钢液和夹杂物变性机理，掌握加压冶金过程中钙、镁处理使钢液中非金属夹杂物无害化的有效方法。探究加压制备的特殊钢材料中镁的赋存状态，及其对晶界易偏聚元素、特殊钢组织和性能的影响规律，阐明镁元素晶界净化和强化机理。研究压力对特殊钢熔体凝固相变、锭与模间气隙形成、冷却速度、局部凝固时间、二次枝晶间距、缩孔和疏松的影响规律，揭示加压凝固组织演变规律，掌握典型特殊钢品种细化晶粒、减少偏析和消除缩孔和疏松的加压凝固技术。通过对加压电渣重熔的微弧渗氮及其机理研究，探索出一种低成本、氮精确可控的氮合金化方法。系统研究加压制备典型特殊钢的组织和性能，揭示氮和易挥发元素在特殊钢中作用机制。通过上述研究，发展特殊钢加压冶金理论，促进加压冶金在高品质特殊钢制备中的应用。

本项目探究了加压下易挥发元素钙、镁在工业纯铁中的溶解热力学和动力学行为，建立了加压下钙、镁元素的溶解度模型；研究了镁对夹杂物的变性机理，开展了加压下镁冶金作用研究，探讨了镁元素对晶粒组织、夹杂物形态及数量、碳化物的影响规律。探讨了压力对相转变、固液相线等凝固参数的影响；揭示了压力强化冷却机制，通过完善不同压力下铸锭枝晶间距及晶粒度的统计以及疏松、缩孔等宏观组织检测，明确了加压促进凝固组织细化的作用机理。建立了加压电渣重熔动态“电-磁-流-热-溶质”耦合数学模型，研究了重熔过程温度场和浓度场的变化规律；揭示电流路径对渣壳形成的影响；建立加压电渣重熔渣皮凝固的数学模型，利用建立的模型研究了电流路径对渣壳厚度的影响，并分析了考虑渣壳形成时的加压电渣重熔过程的热流分配现象，有利于进一步深刻理解加压电渣重熔过程的热量传输现象。开展了加压电渣重熔实验，研究了压力对铸锭凝固和氮的传输过程的影响。分析了电渣重熔气相渗氮、微弧增氮机理，并进行实验研究，掌握了PESR增氮的工艺。研究了加压感应熔炼高氮不锈钢过程中氮含量的精确控制及脱氧脱硫工艺，掌握了加压感应熔炼、加压感应熔炼与加压/保护气氛电渣重熔双联工艺制备高品质高氮不锈钢的关键技术，并成功研发出组织致密、纯净度高、性能优异的系列高氮奥氏体不锈钢和高氮马氏体不锈钢，填补了国内空白；获得了航空马氏体不锈钢30Cr15Mo1N、高端耐蚀塑料模具钢55Cr18Mo1VN、新型高氮热作模具钢ZX007、高氮中熵合金CrCoNiN原型材料；揭示了热处理和合金元素对高氮马氏体不锈钢组织和性能的作用机制，掌握了最佳热处理工艺。探索获得性能优异的超级高氮不锈钢和高氮马氏体不锈钢焊件的搅拌摩擦焊接方法，突破了其难以焊接的难题，为其焊接提供一条新思路和新方法。本项目的开展，建立和发展了特殊钢加压冶金理论，为开发超高强度、超纯净化、高韧性的高品质特殊钢奠定坚实的理论基础，促进加压冶金技术在高品质特殊钢制备中的应用。