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

点击翻译按钮获取中文摘要

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.