Influence of hydrogen on the Phase Transformation behaviour of Low Transformation Temperature (LTT) alloys investigated using ED-XRD

钢在制造、加工和使用过程中会发生氢吸收。这会导致钢的机械性能急剧下降。特别是新开发的高强度钢容易发生氢辅助开裂。几个模型从现象学上描述了氢辅助开裂背后的机制。然而，这些模型是不一致的，并且由于缺乏合适的测量技术，其实验验证往往很差。此外，在已建立的模型中不考虑由多个阶段组成的材料。计划的研究项目重点研究两种具有工业意义的两相高强度钢（低转变温度钢和超马氏体高等级钢）。借助时间分辨和空间分辨的能量色散x射线衍射实验，在拉伸试验中研究了氢对载荷作用下奥氏体向马氏体相变的影响以及氢在两相组织中的扩散。变化的参数是氢浓度和应变速率。通过数据分析，可以确定所施加载荷与相特性（如晶粒尺寸分布、晶体结构和微应力）之间的相关性。这些发现有助于确定氢在机械载荷作用下在两相组织中的扩散路径，以及氢在应变诱导相变和裂纹萌生中的作用。将所得结果与文献中已有的模型进行比较，并对模型在多相微观结构中的适用性进行扩展。

Hydrogen uptake in steels can take place during manufacturing, processing and during service. This can cause a dramatic decrease of the steel's mechanical properties. Especially newly developed and high strength steels are prone to hydrogen-assisted cracking. Several models describe the mechanisms behind hydrogen-assisted cracking phenomenologically. Yet, these models are inconsistent and due to the lack of suitable measurement techniques its experimental validation is often poor. Furthermore, materials consisting of more than one phase are not considered within the established models. The planned research project focuses on two two-phase high strength steels of industrial relevance (Low Transformation Temperature Steel and Supermartensitic High Grade Steel). With help of time- and space-resolved energy-dispersive X-ray diffraction experiments, the influence of hydrogen on the phase transformation from austenite to martensite under load and the hydrogen diffusion in the two phase microstructure will be investigated in tensile tests. The varied parameters are the hydrogen concentration and the strain rate. The data analysis allows identifying the correlation between the applied load and phase-specific properties like grain size distribution, crystal structure and micro stresses. These findings allow identifying the hydrogen diffusion paths under mechanical load in the two-phase microstructure and the role of hydrogen during strain-induced phase transformation and crack initiation. The results will be compared with the existing models from literature and the models will be extended regarding the applicability for multiphase microstructures.