Tailored Carburization: Adjusted mechanical Properties in blank plane and blank thickness direction

该项目的目标是开发和表征有关通过板材局部渗碳来调整局部机械性能的基本可能性。因此，必须开发一种基于表面硬化方法的大块金属成形过程控制策略。因此，在整体金属成形中，表面硬化用于材料的表面硬化，从而增加例如齿轮的齿根和齿侧的疲劳强度。因此，在体积成形中，表面硬化是一种成熟的工艺，而在传统的板料成形中，它是一种新的、创新的方法。因此，完全缺乏用平板金属制造不同碳含量零件的基础知识。然而，对这些不同碳含量的影响和形成的了解是一个关键因素，考虑到由于个别部件中不断上升的部分相互冲突的要求和对功能集成的额外要求，组件和工艺的复杂性不断增加。因此，有必要建立碳在材料中扩散的工艺特定约束的基本关系，并分析与扩散行为相关的不同工艺参数的影响，以确定合适的工艺窗口。由于扩散是一个时变的过程，因此有必要进行额外的研究来分析导致板材整体渗碳的与时间相关的约束条件。如果采用较短的渗碳时间，所产生的力学性能将沿毛坯的厚度方向改变，从而导致不同的裂纹行为，这一点已经通过实例进行了研究。此外，还研究了在炉内停留时间对局部渗碳区和非渗碳区之间过渡区发展的影响，由于局部渗碳区和非渗碳区机械性能的变化，过渡区对产品性能至关重要。此外，不同的模式可以通过导致另一种扩散行为的局部碳浓度来影响所产生的机械性能。由于硬化过程应在刀具中进行，因此必须通过详细的热分析和机械程序来表征附加工艺参数，如施加的接触压力和接触条件。由于石墨的导热系数高于钢的导热系数，而且表面的粗糙度由石墨填充，因此，即使在较低的接触压力下，接触表面也会扩大，因此可以预期石墨支持冷却过程。最后，通过转移到模型几何模型验证了这种新颖的创新方法对金属板材局部渗碳的影响。

The project objective is the development and characterization of the fundamental possibilities regarding the adjustment of local mechanical properties by a localized carburization of sheet metal. Therefore, a process control strategy based on the methodology of case hardening used in bulk metal forming has to be developed. Hereby, in bulk metal forming case hardening is used for surface hardening of the material resulting in increased fatigue strength in tooth root and flank of for example a gear. Thereby, in bulk metal forming case hardening is a well-established process while in conventional sheet metal forming it is a novel, innovative approach. Consequently, fundamental knowledge for the production of components with different carbon content made out of flat sheet metal is missing, totally. The knowledge of the influence and the formation of these different carbon contents, however, represent a critical factor considering the continuing increase in the complexity of the components and processes by rising, partly conflicting requirements and additional demands for functional integration in individual parts. Therefore, it is necessary to develop the fundamental relations regarding process-specific constraints of diffusion of carbon in the material and to analyze the influence of different process parameters related to the diffusion behavior in order to identify a suitable process window. Since diffusion is a time-variant process additional investigations are necessary to analyze the time depending constraints resulting in an integral carburization of the sheet metal. If shorter carburization times are used the resulting mechanical properties will change in thickness direction of the blank leading to a different crack behavior which is investigated exemplarily. In addition, the impact of the residence time in the oven regarding the development of transition zones between locally carburized and not carburized sections is investigated which is crucial for the product performance due to the changing mechanical properties in this area. Furthermore, different patterns can influence the resulting mechanical properties by local concentration of carbon resulting in another diffusion behavior. Due to the fact that, the hardening process should occur in the tool, additional process parameters like applied contact pressure and contact conditions have to be characterized by detailed thermo-analytical and mechanical procedures. It is expected that the graphite is supporting the cooling process due to the thermal conductivity is higher than that of steel and surface asperities are filled by graphite, additionally, resulting in an enlarged contact surface even with lower applied contact pressures. Finally, the identified impacts of the novel, innovative approach regarding the localized carburization of sheet metal are verified by transfer to a model geometry.