Powder bed-based laser beam melting (PBF-LB) for the production of tailored microstructures in quenched and tempered steel 42CrMo4

淬火和回火钢占世界钢铁年产量的很大比例（16-18%），现在可以在许多汽车，航空航天和机械工程部件中找到，如轴，齿轮和其他更高强度的结构件。然而，使用增材制造方法（例如基于激光束的粉末床熔合- PBF-LB）从淬火和回火钢中生产优化组件以及对所产生的材料和组件状态的研究几乎没有取得进展。造成这种情况的主要原因是激光曝光过程中金属粉末固结困难。淬火和回火钢由于含碳量高，通常被认为难以焊接。同样，在PBF-LB工艺中，与微焊类似，由于局部能量输入和相关的自淬，焊缝和热影响区会出现高冷却速率。由冷却速率引起的热应变和相变相关应变导致了构件的强烈变形。焊缝区的马氏体相变也增加了开裂的可能性。裂纹形成的可能性可以减少在过程中使用加热构建板。然而，“建成”状态下的机械性能通常不符合应用程序的技术规范。此外，下游热处理耗时且成本高。因此，该项目的核心是控制PBF-LB工艺中发生的内在转变和回火效应，并专门利用它们将传统热处理和其他下游热处理直接整合到PBF-LB工艺中。除了微观结构和力学特性外，本研究计划将使用特定阶段的热机械有限元模拟来研究新型暴露策略对过程中应力适当，综合和局部热处理的影响。为了验证模拟，还计划在同步加速器上对该过程进行原位表征。这样，就可以弥补热处理钢增材制造领域的一个重要研究空白。

Quenched and tempered steels form a significant proportion of the world's annual steel production (16-18%) and can now be found in many automotive, aerospace and mechanical engineering components such as shafts, gears and other higher strength structural parts. Nevertheless, the production of optimised components from quenched and tempered steels using additive manufacturing methods (e.g. laser beam-based powder bed fusion - PBF-LB) and research into resulting material and component states has made little progress. The reasons for this are mainly to be found in difficulties in consolidation from the metal powder by the laser exposure process. Quenched and tempered steels are generally considered difficult to weld due to their higher carbon content. Also in the PBF-LB process, similar to microwelding, high cooling rates occur in the weld and heat-affected zone due to the local energy input and the associated self-quenching. The thermal and transformation-related strains induced by the cooling rates lead to strong component distortion. The martensitic transformation in the weld zone also increases the probability of cracking. The probability of crack formation can be reduced during the process by using a heated build plate. However, the mechanical properties in the "as-built" state do not usually correspond to the technical specifications from the application. In addition, the downstream heat treatment is time-consuming and cost-intensive. The core of the project is therefore to control the intrinsic transformation and tempering effects occurring in the PBF-LB process and to use them specifically to integrate the conventional and otherwise downstream heat treatment directly in the PBF-LB process. In addition to the microstructural and mechanical characterisation, the present research proposal will use a phase-specific thermal-mechanical FE simulation to investigate the influence of novel exposure strategies with regard to a stress-appropriate, integrated and local heat treatment in the process. To validate the simulation, an in-situ characterisation of the process at the synchrotron is also planned. In this way, an important research gap in the field of additive manufacturing of heat-treatable steels will be closed.