Influence of process-related microstructural and geometrical inhomogeneities on the fatigue behavior of two steel types considering the influence of chemical composition

激光辅助切割以及各种成形工艺是当今几乎应用于每个工业部门的标准制造策略。而在循环变形结构中，材料性能可以根据局部应力分布进行调整，利用所谓的变形诱导塑性在成形过程中，激光切割边缘在大多数情况下导致疲劳强度的有害降低。这也是迄今为止激光切割很少用于循环加载结构的主要原因之一。激光切割刃口的主要特征是毛刺、明显的表面起伏和热影响区，所有这些都与工艺参数密切相关，但也受到被切割材料的薄片厚度和化学成分的影响。变形诱发马氏体形成的亚稳材料的运动硬化也取决于其化学成分。热输入和变形过程都会影响加工过程中的微观组织演变，这反过来又会对疲劳行为的复杂性产生重大影响，从而使循环强度的可靠预测更加困难。考虑到化学成分和工艺参数的影响，将对两种钢（1.0388和1.4301）的显微组织变化进行研究。研究的目的是确定工艺参数和策略，旨在调整微观结构，有利于HCF和VHCF之间过渡范围内的循环强度。这些结果将被用作统计上可靠的疲劳寿命预测的基础，其中一方面，材料物理基于变形引起的硬化和/或转变之间的相互依赖关系，另一方面，由激光切割过程产生的缺口的形成和严重程度将被考虑在内，以更好地理解任何此类加工结构的疲劳行为。

Laser assisted cutting as well as all kinds of forming processes are nowadays standard manufacturing strategies applied in nearly every industrial sector. While in a cyclically deformed structure the material properties can be adjusted according to the local stress distribution by taking advantage of the so called transformation induced plasticity during shaping, laser cutting edges in most cases result in a detrimental reduction in fatigue strength. That is one of the major reasons why laser cutting is up to now barely used for cyclically loaded structures. The key features of a laser cutting edge are burrs, a pronounced surface relief and the heat affected zone, all of which strongly depend on the process parameters, but are also influenced by the sheet thickness and the chemical composition of the material to be cut. The kinematic hardening of a metastable material as a consequence of a deformation induced martensite formation also depends on the chemical composition. Both the thermal input as well as the deformation process will have an influence on the microstructural evolution during the processing, which in turn will have a significant influence on the complexity of the fatigue behavior and therefore makes a reliable prediction of the cyclic strength all the more difficult. For two steels – 1.0388 and 1.4301 – the changes in microstructure as a result of the process steps applied will be investigated considering the influence of the chemical composition and the process parameters. The aim of the investigation is to identify process parameters and strategies that aim at adjusting the microstructure in favor of the cyclic strength in the transition range between HCF and VHCF. The results will be used as basis for a statistically reliable fatigue life prediction, where the material physics based interdependencies between deformation induced hardening and/or transformation on the one hand and the formation and severeness of notches resulting from the laser cutting process on the other hand will be taken into account to get a better understanding of the fatigue behavior of any such processed structures.