Open Access Conference Proceedings

During heat treatment of carburized steel parts, the transformation of austenite to martensite occurs and a certain amount of retained austenite remains in the hardened layers. The higher content of retained austenite in the carburized layer adversely influences hardness and frictional characteristics and increases susceptibility to fatigue damage. Furthermore, retained austenite can transform into deformation induced martensite during service, which provokes changes in properties of the carburized layers. From the technological viewpoint, the content of retained austenite is nearly always monitored but obtained results can be different depending on experimental methods.In this work, the amount of retained austenite in carburized layers of manganese-chromium steels was evaluated by image analysis method, by X-ray diffraction and also by EBSD. The largest amount of retained austenite was measured using the technique of X-ray diffraction, i.e. 28 %. The amount of retained austenite measured by image analysis of metallographic images was 13 %. However, the results of image analysis greatly depend on the metallographic preparation of samples, digital image processing and the grayscale level settings for the calculation of the retained austenite content. The lowest amount of retained austenite was determined by EBSD, i.e. 5 %. Even in this case the values depended on the method of scanned data processing. No method used to determine the amount of retained austenite in the carburized layer is universal and largely depends on the sample preparation and partial steps performed in individual measurement methods.

Keywords: Retained austenite, carburized layers, image analysis, X-ray diffraction, EBSD

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