高压环境氢与交变荷载耦合作用下应变强化奥氏体不锈钢多尺度疲劳损伤研究

In hydrogen energy, petroleum and chemical industries, bearing parts of high pressure hydrogen systems are often made of strain strengthening metastable austenitic stainless steels, however, this kind of parts are prone to fatigue damage in the coupling effect of strain strengthening, high pressure hydrogen gas and alternating load. Controlling the deformation microstructure reasonably caused by strain strengthening is the key to prevent hydrogen induced fatigue damage. Recently, the applicant found that strain strengthening in a specific condition (200℃ warm rolling) could prevent the fatigue crack initiation of austenitic stainless steels in the high pressure hydrogen gas environment, which provides a new path to obtain structural materials with high strength and high hydrogen embrittlement resistance. The key to realize this method is to reveal the associated mechanism between hydrogen induced multiscale fatigue damage and the deformation microstructure caused by strain strengthening. Therefore, we plan to study the dependences of hydrogen transportation, hydrogen distribution and fatigue damage on the deformation microstructures caused by strain strengthening and strain localization near the crack tip, by using strain induced hydrogen release, hydrogen microprint, secondary ion mas spectrometry and other experimental methods. Combined with the numerical analysis in the multi-field coupling (hydrogen concentration field, stress and strain field), we try to reveal the dynamic mechanism of hydrogen transportation caused by the deformation microstructure and hydrogen segregation near the crack tip, and establish the associated mechanism among the deformation microstructure, hydrogen transportation and multiscale fatigue damage. It is clear that this research work will provide the guarantee for safe utilization of high pressure hydrogen systems.

石化和氢能领域中高压氢系统承载件常采用应变强化亚稳奥氏体不锈钢，然而该类承载件在应变强化残余影响、高压氢气和交变载荷耦合作用下易发生疲劳损伤。应变强化导致形变组织（位错、应变诱发马氏体、形变孪晶）的合理调控是氢致疲劳损伤预防的关键。最近申请人发现，在高压氢环境中特定条件的应变强化（200℃温轧）会阻止奥氏体不锈钢疲劳裂纹的萌生，这提供了一个获取高强度、耐氢脆结构材料的新途径。该技术方法实现的关键在于解明应变强化导致形变组织与氢致多尺度疲劳损伤的关联机制。本项目拟采用应变诱导氢释放、氢微观印刷、二次离子质谱等技术，研究应变强化和裂尖局域化形变组织对氢传输行为、氢分布特征、疲劳损伤的影响规律；结合多场（氢浓度场、应力应变场）耦合作用下的数值分析，揭示形变组织导致的氢传输和裂尖附近氢偏聚的动力学机制，建立形变组织-氢传输-多尺度疲劳损伤三者之间的关联机制。该研究将为高压氢系统的安全利用提供保障。

发展氢能和清洁利用化石能源是我国能源战略的重要组成部分。高压氢系统，即介质中含有高压氢气的系统，是氢能储存、输运和利用的核心装备，具有介质易燃易爆、失效机理复杂等特征。高压氢系统承载件常采用应变强化亚稳奥氏体不锈钢，然而该类承载件在应变强化残余影响、高压氢气和交变载荷耦合作用下易发生疲劳损伤。应变强化导致形变组织（位错、应变诱发马氏体、形变孪晶）的合理调控是氢致疲劳损伤预防的关键。本项目以应变强化奥氏体不锈钢为研究对象，通过研究高压氢环境下应变强化和裂尖局域化形变组织对氢传输行为、氢分布特征、氢致疲劳损伤的影响，探讨应变强化导致形变组织与氢致多尺度疲劳损伤的关联机制。通过研究，获得3个重要结论：①.可视化展现了应变诱导马氏体所引起马氏体/奥氏体相界氢偏聚现象，并揭示应变诱导马氏体对氢传输的影响规律。研究了三种（预应变、动力学、裂尖）应变诱导马氏体各自对氢致开裂所起的作用，发现裂尖应变诱导马氏体内的微裂纹和微孔是导致氢致裂纹加速的主要原因；②.解明了奥氏体不锈钢成形制造–微观组织–氢传输–氢致开裂的关联机制。疲劳裂纹扩展过程中变形孪晶和动力学应变诱导马氏体的形成会促进氢在界面处的富集和偏聚，进而加速氢致裂纹扩展；③.利用温轧调控微观组织，打破了“强度---氢脆”的平衡妥协，在高强度基础上提高了奥氏体不锈钢的抗氢脆性能。本研究不仅加深了对高压氢环境下奥氏体不锈钢多尺度损伤演化机理的理解，而且为高压氢系统用候选材料的选定、材料成型工艺的优化提供理论指导；同时，本研究将有助于开发出拥有自主知识产权的耐氢脆、使用寿命长、安全性高的高压氢系统关键零部件产品，缩小我国高压氢系统与发达国家的差距。