Fatigue life reduction of steels in pressurized hydrogen as a consequence of changes in short crack propagation mechanisms

尽管进行了许多研究活动，但氢引起的材料损伤仍然没有得到清楚的理解。一方面，氢致损伤过程受材料、载荷和环境等多种因素的影响。另一方面，氢脆的主要机制（HELP HEDE，AIDE，HESIV以及压力理论）可以以组合的方式发生，因此不同的脆化机制在材料损伤演化的不同阶段占主导地位。此外，氢脆在循环加载的情况下，仍然缺乏基本的investigations.Within的框架内，拟议的研究项目，氢致材料损伤的机制，不同类型的钢在低周和高周疲劳制度的特点和代表性的微观结构为基础的模型可用于模拟计算。出于实际原因，选择了来自不同应用领域的两种钢，其具有不同的微观结构和对氢吸收的敏感性，即，亚稳奥氏体钢X2CrNi19 - 11和软马氏体钢X3CrNiMo13 - 4。这些钢的一个广泛的数据库是可用的，描述了不同参数对氢条件下的机械性能的影响。真空中的疲劳试验将作为在加压氢气和氦气中获得的试验结果的参考。详细的金相和断口微观结构的调查是为了显示氢对材料损伤过程（位错排列，短裂纹生长和相变的变化）的影响。因此，损伤的演变将被监测的起始位置和整个疲劳寿命的主要部分损伤的发生频率从微观结构的短裂纹的形成，直到过渡到长crack propagation.The实验表征的氢致损伤机制将被转移到一个基于物理的模拟模型。通过将所识别的损伤机制包括到已经存在的短裂纹模型中，该模型基于边界元法，将系统地描述氢对微观结构损伤演化的影响。通过这种方式，建模有助于提高对氢影响下材料损伤的理解。实验结果和模拟模型的发展都将提供一个良好的基础，更好地利用材料的组件暴露于氢，并将大大有助于一个无误的材料调整耐氢微观结构。

Material damage resulting from hydrogen is still not clearly understood despite many research activities. On the one hand, the hydrogen-induced damage processes are influenced by many factors which are specific to material, loading and environment. On the other hand, the main mechanisms of hydrogen embrittlement (HELP HEDE, AIDE, HESIV as well as pressure theory) can occur in a combined manner, so that different embrittlement mechanisms are dominating in different stages of material damage evolution. Moreover, hydrogen embrittlement in the case of cyclic loading is still lacking fundamental investigations.Within the framework of the proposed research project, the mechanisms of hydrogen-induced material damage of different types of steel in the low and high cycle fatigue regime will be characterized and represented in a microstructure-based model usable for simulation calculations. For practical reasons, two steels from different application areas were selected with different microstructures and susceptibility to hydrogen absorption, i.e., the metastable austenitic steel X2CrNi19-11 and the soft-martensitic steel X3CrNiMo13-4. An extensive database for these steels is available, describing the effect of different parameters on the mechanical properties under hydrogen conditions. Fatigue tests in vacuum will serve as reference for the test results obtained in pressurized hydrogen and helium. Detailed metallographic and fractographic microstructural investigations are intended to show the effect of hydrogen on the material damage process (change in the dislocation arrangement, short crack growth and phase transformation). Thus, the damage evolution will be monitored regarding initiation site and frequency of occurrence of damage throughout the major part of fatigue life starting from the formation of microstructurally short cracks until the transition to long crack propagation.The experimentally characterized hydrogen-induced damage mechanisms will be transferred into a physically-based simulation model. By including the identified damage mechanisms into an already existing short crack model, which is based on the boundary element method, the effect of hydrogen on the microstructural damage evolution will be described systematically. In this way, the modeling contributes to the development of an improved understanding of material damage under the influence of hydrogen. The experimental results and the development of the simulation model will both provide a sound basis for a better material utilization in components being exposed to hydrogen and will strongly contribute to an unerring material adjustment towards hydrogen-resistant microstructures.