Abstract
Induction surface hardening is a process often used in industrial applications to efficiently increase the lifetime of components. Recently, this process has been enhanced with the inductive short time austempering process, creating a martensitic-bainitic microstructure. It is well-known that in homogeneous mixed microstructures, an optimally adjusted volume fraction of bainite can significantly increase the lifetime of the components even further. Regarding inductive short time austempering, there is a lack of knowledge in characterizing and differentiating graded microstructures, which occur due to the temperature gradients within the process. Therefore, three methods were investigated: the analysis of the grayscale profile of metallographic sections, the hardness profile and the full width at half maximum (FWHM) profile from the intensity curve (rocking curve) of the X-ray diffraction pattern. These methods were initially applied to homogeneous structures and evaluated. The findings were then transferred to graded microstructures. Finally, the graded microstructures could be differentiated both via the hardness profile and the FWHM value, while the grayscale analysis only allowed qualitative statements to be made. It became evident that both the volume fractions and their structure are crucial for subsequent mechanical characterization. Since the martensitic microstructure is easier to identify, it serves as a reliable reference for evaluating the mixed microstructure. In summary, these findings offer the foundation for further characterization of graded martensitic-bainitic mixed microstructures.
