Experimental and numerical assesment of the influence of hydrogen and microstructure on the fatigue behavior of duplex steels

在能源转型的背景下，双相钢越来越多地被用于海上技术领域，它们通过阴极极化暴露在氢的影响下。这可能会导致双相钢的氢脆开裂。氢在双相钢两相组织中的作用是极其复杂的。由于两相的弹塑性性质不同，在相界面处产生内应力，影响氢的扩散。在上一个DFG项目“循环加载过程中单晶和多晶加工硬化效应(包辛格效应)的实验和数值分析”中，对影响1.4462双相钢循环塑性行为的与显微组织有关的各种因素进行了实验和数值分析。然而，目前的研究还没有考虑这些因素对双相钢在循环载荷作用下氢脆的影响。可以认为，循环载荷作用下的非均匀应力分布会影响氢在两相双相组织中的扩散，导致疲劳损伤演化依赖于循环时间、整体和局部氢浓度。因此，本项目的目的是了解材料和加载历史之间的相互作用对双相钢氢脆的影响。通过对相互作用的了解，可以通过优化两相微结构来根据应用条件具体定制材料性能，并可以提高部件寿命。本课题采用实验和数值分析相结合的方法，对双相钢的氢脆行为进行了研究。RWTH亚琛大学的实验研究包括氢脆的量化和不同组织条件下的失效机理分析。对影响因素进行了系统的相关性分析和评价。此外，在微观结构尺度上对观察到的效应的原因进行了研究，并采用了先进的分析方法。在这里，基于奥芬堡应用科学大学微观结构敏感模型的计算分析做出了重要的解释性贡献。这些模型包括关于多晶微观结构的统计信息，并使用单晶塑性模型来进行循环加载。采用循环载荷作用下的力学和扩散耦合计算，实现了对内部应力和氢浓度的局部分析，从而可以确定微观结构中关于氢脆的临界局部状态。

In the context of the energy turnaround, duplex steels are increasingly used in the field of offshore technology, where they are exposed to the influence of hydrogen through cathodic polarization. This can lead to cracking in duplex steels as a result of hydrogen embrittlement. The effect of hydrogen in the two-phase structure of duplex steel is extremely complex. Due to the different elastic-plastic properties of the two phases, internal stresses occur at the phase boundaries, which influence hydrogen diffusion. In the preceding DFG project "Experimental and Numerical Analysis of Work Hardening Effects in Single- and Polycrystals during Cyclic Loading (Bauschinger Effect) ", various factors related to the microstructure influencing the cyclic plasticity behavior of the duplex steel 1.4462 were analyzed and quantified both experimentally and numerically. However, the influence of these factors on hydrogen embrittlement in duplex steel under cyclic loading is not considered in the current state of research. It can be assumed that the transient inhomogeneous stress distribution under cyclic loading affects the hydrogen diffusion in the two-phase duplex microstructure and leads to a fatigue damage evolution dependent on the cycle time and the global and local hydrogen concentration. Therefore, the objective of this project is to gain an understanding of the interaction of material and loading history on hydrogen embrittlement of duplex steels. With an understanding of the interaction, material properties can be specifically tailored to application conditions by optimizing the two-phase microstructure, and component life increases can be achieved. In this project, the investigation of hydrogen embrittlement in duplex steel is achieved by a combined approach of experimental and numerical analyses. The experimental investigations at RWTH Aachen University include quantification of hydrogen embrittlement and analysis of failure mechanisms for different microstructural conditions. Influencing factors are systematically analyzed and evaluated with respect to their relevance. In addition, the causes of the observed effects are investigated on a microstructural size scale and advanced analysis methods are applied. Here, computational analyses based on microstructure-sensitive models of Offenburg University of Applied Sciences make an essential explanatory contribution. The models include statistical information on the polycrystalline microstructure and use a single crystal plasticity model for cyclic loading. The coupled calculation of mechanics and diffusion under cyclic loading implemented in the project enables the local analysis of internal stresses and hydrogen concentrations, from which critical local states in the microstructure regarding hydrogen embrittlement can be identified.