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

该项目的目标是开发和描述通过局部渗碳金属板来调整局部机械性能的基本可能性。因此，必须开发一种基于壳体硬化方法的金属体成形过程控制策略。因此，在大块金属成形情况下，硬化用于材料的表面硬化，导致例如齿轮的齿根和侧面的疲劳强度增加。因此，在大块金属成形中，硬化是一种成熟的工艺，而在传统的钣金成形中，硬化是一种新颖的、创新的方法。因此，生产由平板金属制成的具有不同碳含量的部件的基本知识完全缺失。然而，考虑到组件和工艺的复杂性不断增加，个别部件的要求不断增加，部分相互冲突，以及对功能集成的额外要求，对这些不同碳含量的影响和形成的了解是一个关键因素。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，并分析不同工艺参数对扩散行为的影响，以确定合适的工艺窗口。由于扩散是一个时变过程，需要额外的研究来分析导致金属板整体渗碳的时间依赖约束。如果使用较短的渗碳时间，则产生的力学性能将在毛坯厚度方向上发生变化，从而导致不同的裂纹行为，并对其进行了实例研究。此外，还研究了在烘箱中停留时间对局部渗碳和未渗碳部分之间过渡区发展的影响，由于该区域机械性能的变化，过渡区对产品性能至关重要。此外，不同的模式可以通过局部碳浓度影响最终的力学性能，从而导致另一种扩散行为。由于硬化过程应该发生在工具中，附加的工艺参数，如施加的接触压力和接触条件，必须通过详细的热分析和机械程序来表征。由于导热性比钢高，并且表面凹凸不平由石墨填充，因此可以预期石墨支持冷却过程，此外，即使施加的接触压力较低，也可以扩大接触面。最后，通过转移到模型几何来验证关于金属板局部渗碳的新颖创新方法的确定影响。

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.