In-situ characterization of a locally carburized complex phase steel for manufacturing of tailored semi-finished products

• Applicant: Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450281370

Hot stamping has established itself as a manufacturing process for safety-critical components. A further improvement in passenger safety can be achieved by locally adjusting the mechanical properties. This is based on the combination of high-strength zones for penetration protection in the interior and ductile zones, which enable energy absorption due to the higher residual deformation capacity. One method of tailoring is the local carburization of the semi-finished product. Due to the regional modification of the chemical composition, this process offers several advantages over welding- and temperature-based methods. For example, the design of the zones to be adjusted is very flexible due to the small transition areas. In addition, the process is independent of complex furnace and tool technology and is therefore particularly suitable for tailoring the properties of small series components. In addition to the strength-enhancing function of the additionally absorbed carbon, it also influences the phase transformation temperatures of the steel. This property is still uninvestigated in tailored carburization. Based on this effect, a greater gradation between carburized and non-carburized areas can be achieved by a suitable setting of the austenitizing temperature. The overall aim of the project is therefore to develop a fundamental scientific understanding of the process. The influence of the carburizing parameters on the transformation temperatures is to be analyzed first. Based on this, a process corridor of the austenitization temperature can be identified as a function of the respective carburization. On the basis of this, the effect of varying the carburization parameters and the austenitization temperature on the mechanical properties of carburized and non-carburized samples will be investigated. The obtained results in combination with the in-situ characterization of the microstructural changes via laser ultrasound measurments will be used to identify a process window. In addition, the prediction accuracy of the numerical simulation is to be improved based on the in-situ characterization and the hot flow behavior, taking into account the process-specific influencing variables. The extended material models will be validated and verified using real demonstrator components. Furthermore, the demonstrator components, which have different carburized zones and were manufactured with various process parameters, are to be examined with regard to their energy absorption capacity using three-point bending tests and crash tests. Finally, a process evaluation and guidelines are to be derived with regard to the achievable grading using the method examined.

• DFG Programme: Research Grants