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

该项目的目标是开发和表征通过金属板局部渗碳调整局部机械性能的基本可能性。因此，必须开发一种基于块状金属成形中使用的表面硬化方法的过程控制策略。因此，在块体金属成型中，表面硬化用于材料的表面硬化，从而提高例如齿轮的齿根和侧面的疲劳强度。因此，在块状金属成型中，表面硬化是一种成熟的工艺，而在传统的金属板材成型中，它是一种新颖的创新方法。因此，完全缺乏由平板金属制成的具有不同碳含量的部件的生产基础知识。然而，考虑到由于不断增加的部分冲突的要求以及对各个部件的功能集成的额外要求，部件和工艺的复杂性不断增加，了解这些不同碳含量的影响和形成是一个关键因素。因此，有必要建立有关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。由于扩散是一个随时间变化的过程，因此需要进行额外的研究来分析导致金属板整体渗碳的时间相关约束。如果使用较短的渗碳时间，则所得的机械性能将在毛坯的厚度方向上发生变化，从而导致不同的裂纹行为，对此进行了示例性研究。此外，还研究了炉中停留时间对局部渗碳和未渗碳部分之间过渡区域发展的影响，由于该区域机械性能的变化，这对于产品性能至关重要。此外，不同的图案可以通过局部碳浓度影响最终的机械性能，从而导致另一种扩散行为。由于硬化过程应在工具中进行，因此必须通过详细的热分析和机械程序来表征附加的工艺参数（例如施加的接触压力和接触条件）。由于石墨的导热率高于钢，并且石墨填充了表面凹凸不平，因此预计石墨将支持冷却过程，此外，即使施加的接触压力较低，也会导致接触表面扩大。最后，通过转移到模型几何形状来验证新颖、创新的金属板局部渗碳方法的影响。

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.