Microstructural evaluation of the defect tolerance of Cu alloyed steels under cyclic loading

循环加载下铜合金钢缺陷容限的显微组织评价

• 批准号: 335746905
• 负责人: Professor Dr.-Ing. Tilmann Beck
• 金额: --
• 依托单位: Lehrstuhl für Werkstoffkunde (WKK)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/335746905?language=en
• 关键词: Microstructural; evaluation; defect; tolerance; Cu

In the previous project, hardness, tensile and fatigue strength as well as defect tolerance of the 2 wt.% Cu alloyed steels X0.5CuNi2-2 (0.005 wt.-% C – „X0.5“) und X21CuNi2-2 (0.21 Ma-% C – „X21“) was increased by heat-treatment-induced formation of Cu precipitates. The resulting mechanical properties depend on the precipitation state, which includes size, number, lattice structure and chemical composition of the Cu precipitates. While for the ferritic steel X0.5 the influence of the precipitation state on defect tolerance was clearly shown, the relationship between defect tolerance and precipitation state of the ferritic-pearlitic steel X21 is more complex, which was addressed by different evaluation methods (e.g. √area-concept, Kitagawa-Takahashi diagram). The overall research aim of the proposed project is a deeper understanding of the relationship between precipitation state and resulting fatigue properties beyond the actual state-of-knowledge. This shall first be achieved for the steel X0.5. An essential prerequisite to reach this research aim is a sound knowledge of the influence of coherency relationship as well as chemical composition of the phase boundary between Cu precipitate and base material. It was shown in the previous project that this knowledge is essential for a better understanding of the complex relationships between Cu precipitation state and mechanical properties, especially fatigue behavior. Current research shows that the stability of Cu precipitates depends on the applied amount of plastic deformation. Therefore, the dependency of defect tolerance on fatigue regime will be analyzed by LCF, HCF and VHCF fatigue tests. Based on the already existing HCF results, the focus of the proposed work will be on LCF loadings with high strain amplitudes and the VHCF regime characterized by local cyclic microplasticity. Particular attention will be paid to defect tolerance and the underlying microstructural mechanisms. These investigations will be extended by in-situ crack initiation and propagation experiments for analyzing the damage mechanisms. To develop a thorough understanding of these relationships, the fatigue experiments will be combined with high-resolution microstructural analysis (TEM and 3D atom probe), which enables, amongst others, investigating the interaction between precipitates and dislocations. In addition to the examination at the X0.5 steel, the local influences on the defect tolerance of the ferritic-pearlitic steel X21, observed in the previous work, shall be clarified. For this, interrupted fatigue experiments will be conducted, enabling the localization of the crack initiation site and the definition of damage mechanisms. Moreover, using instrumented cyclic nanoindentation tests, the hardening potential of ferrite and pearlite grains will be determined. Combined with atom probe tomography within these microstructural constituents, their individual precipitation states can be consistently evaluated.

在以前的项目中，硬度、拉伸和疲劳强度以及2 wt.%的缺陷容限Cu合金钢X0.5CuNi2-2（0.005重量% C-nX 0. 5”）和X21 CuNi 2 -2（0.21Ma-% C-nX 21”）的热处理诱导的Cu沉淀物的形成增加。所得的机械性能取决于沉淀状态，其包括Cu沉淀物的尺寸、数量、晶格结构和化学组成。对于铁素体钢X0.5，析出状态对缺陷容限的影响被清楚地显示，而铁素体-珠光体钢X21的缺陷容限和析出状态之间的关系更加复杂，这通过不同的评估方法（例如，面积概念，北川-高桥图）来解决。该项目的总体研究目标是更深入地了解沉淀状态与疲劳性能之间的关系。这应首先在X0.5钢上实现。实现这一研究目标的一个必要前提是充分了解Cu沉淀物与基体材料之间的相界的化学成分以及共格关系的影响。在以前的项目中表明，这些知识对于更好地理解Cu沉淀状态与机械性能，特别是疲劳行为之间的复杂关系至关重要。目前的研究表明，Cu析出相的稳定性取决于塑性变形量。因此，将通过LCF、HCF和VHCF疲劳试验来分析缺陷容限对疲劳状态的依赖性。基于现有的HCF结果，建议的工作重点将是低周疲劳载荷与高应变幅和VHCF制度的特点是局部循环微塑性。将特别注意缺陷容忍度和潜在的微观结构机制。这些调查将通过原位裂纹萌生和扩展实验来分析损伤机制。为了深入了解这些关系，疲劳实验将与高分辨率显微结构分析（TEM和3D原子探针）相结合，这使得除其他外，研究沉淀物和位错之间的相互作用。除了对X0.5钢进行检查外，还应澄清在先前工作中观察到的对铁素体-珠光体钢X21缺陷容限的局部影响。为此，将进行中断疲劳实验，使裂纹萌生部位的本地化和损伤机制的定义。此外，使用仪器化的循环纳米压痕试验，铁素体和珠光体晶粒的硬化潜力将被确定。结合这些微观结构成分的原子探针断层扫描，它们的个别沉淀状态可以得到一致的评价。