Detection of Non-Metallic Inclusions in Steel by X-ray Computed Tomography and After Fatigue Testing

摘要

Non-metallic inclusions like Al_2O_3, CaO or CaS determine to a high amount the quality and cleanness of steels, which is of increasing importance for high-quality steelmaking. Inclusions are often the reason for the functional failure especially in dynamic stressed components made of steels. Therefore, it is important to have accurate, fast and reproducible characterization methods to detect such inclusions in Fe-alloys. Within this paper we compare two different methods: detection of non-metallic inclusions (NMIs) by first X-ray micro computed tomography (CT) and second fatigue life testing. The evaluation of CT-data of Fe-based materials can be rather difficult, because of the high absorption and penetration lengths limits and since CT-results of Fe-alloys are usually prone to image noise, offer poor contrast and the interpretation is affected by artefacts. Suitable scan parameters as well as evaluation routines are presented and rules for the detectability and classification are specified. The degradation of steel samples by oscillation fatigue life testing is a way to measure the appearance of harmful NMIs. If there is a NMI of critical size in the test sample, a functional failure occurs and the fracture surface can be investigated by scanning electron microscopy (SEM). The chemical composition of the NMI is measured by energy dispersive X-ray spectroscopy (EDX) to identify the type of the inclusion.