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型工艺是当今几乎所有工业部门应用的标准制造策略。虽然在循环变形的结构中，材料性能可以根据局部应力分布通过利用成形期间所谓的相变诱导塑性来调整，但在大多数情况下，激光切割边缘导致疲劳强度的有害降低。这也是激光切割至今很少用于循环载荷结构的主要原因之一。激光切割刃的主要特征是锯齿、明显的表面浮雕和热影响区，所有这些都强烈依赖于工艺参数，但也受到板材厚度和待切割材料化学成分的影响。由于形变诱发马氏体形成的亚稳材料的运动硬化也取决于化学成分。热输入以及变形过程都将对加工过程中的微观结构演变产生影响，这反过来又将对疲劳行为的复杂性产生重大影响，因此使得可靠地预测循环强度变得更加困难。对于两种钢-1.0388和1.4301-显微组织的变化，作为应用的过程步骤的结果将进行研究，考虑到化学成分和工艺参数的影响。调查的目的是确定工艺参数和策略，旨在调整有利于循环强度之间的过渡范围内的HCF和VHCF的微观结构。这些结果将被用作统计可靠的疲劳寿命预测的基础，其中，一方面将考虑基于材料物理学的变形诱导硬化和/或转变与另一方面激光切割过程产生的切口的形成和粗糙度之间的相互依赖性，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.