基于氮配分的超低碳马氏体不锈钢纳米级逆变奥氏体形成机理及复合强韧化

Super-martensitic stainless steel is the key material for the oil and gas exploitation and transportation due to the comprehensive advantage of good corrosion resistance, formability and weldability. However, the current levels of strength and ductility cannot satisfy the needs of ultra-high strength and ductility for ultra-deep well oil/gas pipe materials. Therefore, the study on super-martensitic stainless steel with ultra-high strength and ductility has essential applied value. This proposal takes the super low carbon Cr13 martensitic stainless steel as the research object. An alternative approach of N-V allolying and high temperature quenching and low temperature nitrogen partitioning technology is presented. The effects of N on the formation and evolution of reversed austenite precipitated on interfaces of M/Ar and M/M, thermodynamics of N enrichment in retained austenite and kinetics of N-V compounds will be studied to control the nitrogen partitioning between the lath martensite and austenite effectively. Nanoscale reversed austenite will be obtained at the interfaces between martensite and retained austenite. The influence in dispersion strengthened of N-V compound is also focused on. Based on this, the microstructure and performance of SMSS must be improved, and compensatory mechanism of strengthening-toughening will be investigated thoroughly, the designing and controlling of the fine microstructure with an optimal strength-toughness property can be reached. In this project, the innovation of dynamic nitrogen partitioning is proposed for the first time. The driving forces for nanoscale reversed austenite are determined by local chemical equilibrium. The mechanism of reversed austenite will be revealed and effective control could be realized. The research work has great theoretical significance.

超级马氏体不锈钢以良好的耐蚀性、成型性及焊接性等综合优势成为油气开采及运输的关键材料，但其强度和韧度水平无法满足目前深井、超深井油气管用材所需超高强韧性能的要求。因此，研究开发具有超高强韧性能的超级马氏体不锈钢具有重要的应用价值。本申请拟以超低碳Cr13马氏体不锈钢为研究对象，采用氮、钒合金化技术，通过高温快速淬火-低温配分工艺，深入研究配分过程中N对M/A残界面及M/M晶界上逆变奥氏体生成及演化、残留奥氏体中N富集相关的热力学及氮钒化合物形成动力学等问题，达到有效控制氮在板条马氏体和奥氏体中的分配。利用动态氮配分形成纳米级逆变奥氏体增韧，辅以氮钒化合物析出强化，揭示多相结构的复合强韧化机理，实现微观结构的调控和最优设计，获得超高强韧性能。项目首次提出利用动态氮配分实现马氏体与奥氏体界面的局部平衡以形成纳米级逆变奥氏体，揭示其形成机制并实现有效调控，该研究具有重要的科学理论意义。

针对目前超级马氏体不锈钢强韧性能偏低，难以满足油气开采、运输领域用管材所需的性能要求难题，本项目以超低碳马氏体不锈钢为研究对象，分别采用氮、锰、钒合金化技术，系统地研究了高温快速淬火-低温配分过程中的不同元素对晶粒细化、M/A界面与M/M晶界上逆变奥氏体生成及稳定性的影响规律；揭示了稳定性不同的残余奥氏体和逆变奥氏体在拉伸过程中进行着更为连续的TRIP效应，实现了动态氮配分形成的纳米级逆变奥氏体增韧；深入分析了分布均匀的VN相所表现出的优异弥散强化作用，显著提升了马氏体不锈钢的力学性能，阐明了强韧化机理；明晰了以不锈钢中马氏体与奥氏体界面的局部平衡为手段，获得纳米级别逆变奥氏体的新思路；相关研究成果不但为超级马氏体不锈钢内部纳米强化相的精确调控提供了新的途径和指导原则，更对于未来油气工程领域中的高性能马氏体不锈钢设计与开发具有重要的实际意义。