原位纳米增强高强韧钢及其复杂海洋环境适应性研究

High strength and toughness steel is paid more and more attention in the applications of large scale engineering equipment in the complex marine environment. However, the higher the strength of steel, the more difficult the welding, and the greater the sensitivity of hydrogen embrittlement. This project will research the optimal design of alloy based on the mechanism of hydrogen embrittlement and the coupling of the minor elements. The law of nano particle initiation and distribution will be studied during solidification to make clear the action mechanism of trace elements, such as Nb,V,Al,Ti,C,N,O in different temperatures. The size, shape and distribution of nano particles formed during the process will be controlled in order to get dispersion nano-particle strengthened steels. The nano particles are difficult to dissolve and grow up in the welding because of the high melting point of the oxides. This is benefit to the improvement of the welting soften problem. The dispersion nano phase not only play strengthening effect, but also trap hydrogen in the grain to avoid continuous distribution along the grain boundaries, accordingly, to improve strength and toughness, reduce the sensitivity of hydrogen embrittlement significantly . .Systematic evaluation the environmental suitability of the nano-particle strengthened high toughness steel in the complex marine environment. The relationship of nanometre precipitated phase and pitting corrosion in ocean atmospheric environment with high temperature, high humidity, high salt and in alternation of wetting and drying environment will be researched. The special performance of cathodic protection, hydrogen embrittlement and pitting corrosion of the steel in high hydraulic pressure of deep sea will be studied, in order to provide theoretical and technical support for exploit the high strengthening , high toughness, easily welted, low environmental sensitivity steel in the application in the marine structure.

高强韧钢是大型海洋工程装备用钢的主要发展方向。然而，高强钢的氢脆是制约其在复杂海洋环境中应用的瓶颈。本申请基于氢脆机理和多元微量元素耦合理论，进行成分的精准设计，研究钢熔体和凝固过程中原位纳米相的形成规律，阐明多元微量元素(Nb,V,Al,Ti,C,N,O)在不同温区的固溶-析出机制，建立微量元素与第二相的定量关系，并对原位纳米相的微结构与分布建立调控机制，制备出高熔点、高度弥散（间距~10nm）的细小（2~5nm）氧化物纳米析出相，在提高强韧性的同时即可改善焊接软化问题，又可把氢固定在晶内，不在晶界形成连续分布，从而达到降低氢脆敏感性的作用。系统评价纳米增强高韧钢在复杂海洋环境中的适应性，研究高温高湿高盐海洋大气环境和干湿交替区纳米析出相与点蚀的相关性，以及深海高静水压对点蚀、氢脆和阴极保护的影响规律，为开发高强韧、易焊接、环境敏感性低的深、远海工程用钢提供理论支撑。

本项目基于化学平衡理论的多元微量合金设计理念，建立了Fe-M1(Nb，V，Ti)-C-N-O系钢中互溶与不互溶多元第二相平衡固溶的热力学分析模型并对海洋工程用钢进行多元微量合金设计和优化。根据不同的冶炼装备状况精准设计微合金成分及含量，突破熔体中非对称剪切流理论和微合金局域供给技术，创新性地提出在熔体和凝固过程中分步分温区形成大量弥散分布的原位氧化物纳米析出技术，获得颗粒尺寸小（2~5nm）、弥散度高（颗粒间距~10nm）的氧、碳、氮化物纳米相，不仅能显著增强、增韧，还能改善焊接性能。结合原位扫描开尔文探针力显微镜和球差校正透射电子显微镜技术，研究了高强度低合金钢中纳米析出相与马氏体基体界面的氢捕获行为及其内在机理。发现并非所有非共格界面都捕获氢，有些甚至排斥氢；析出相表面的碳/硫空位和近邻基体中的应变场很可能决定了界面的氢捕获特征。这些发现澄清了过去对非共格析出相是否能捕获氢问题的争议，为纳米析出相俘获氢机理提供了直接实验证据和一种有效的原位方法。从原子层次阐明了纳米析出相与氢的交互作用，并揭示了α-Fe/NbC半共格界面处的失配位错核心是深氢陷阱。通过自制的海洋环境模拟装置，系统地研究了纳米增强高韧钢在复杂海洋环境中的适应性，验证了基于弥散纳米相氢陷阱理论开发的海洋工程用钢能够显著降低高强钢的氢脆敏感性和提高抗腐蚀疲劳性能，有望用于舰船和深潜器的制造。