EVALUATION OF ALTERNATIVE MICROCLEANLINESS METHODS

This study focuses on the development and comparison of standard- and alternative methods to evaluate the Micro-cleanliness of tool steels on a microscopic level. The steels subjected to this study are hot working- and plastic mould steels produced by an electric arc furnace (EAF) and ladle furnace (LF). After re-melting by an electric slag (ESR) or a vacuum arc (VAR) furnace the forged or rolled specimen were taken as subject for the investigation with different methods. The standard investigation method for non-metallic inclusions (NMI) is light optical microscopy (LOM). Upon giga cycle fatigue (GCF) tests, the NMI are additionally investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS), electrolytic extraction method and X-ray computed tomography (XCT) with a maximum resolution of 1 µm voxel size. For comparative results the specimens used for XCT experiments (diameter of approx. 2 mm and length of approx. 20 mm) were destructively investigated with automated LOM. XCT for NMI is a reliable method. The inhomogeneities, which were found, are NMI and no digital artefacts or pores. Comparative results for the different production routes show a similar size of NMI within each method. Each method has its advantages and disadvantages concerning additional information, e.g. time for preparation and measurement and costs.