As part of the diploma work, we analysed the microstructure of an induction hardened roll, made out of OTV1C tool steel. This type of steel is often used for the manufacturing of rolls for cold rolling with the necessary wear resistance of the surfaces. Its basis lies in appropriately large and evenly distributed carbides of different types. The test roll was induction hardened with different parameters – we changed the austenitization temperature and the speed of hardening. Discs were then cut from the test roll and samples were made from this. The samples were ground, polished and finally etched. Samples prepared in this way were examined under a light microscope, a Scanning Electron Microscope SEM and the grain size was determined according to the ASTM E112 standard.
In the investigation and the analysis of the results, we focused on the size and distribution of carbides in the samples of investigated steel. We used modern investigative methods, such as light and electron microscopy, X-ray phase analysis and study of important phase diagrams. We found out that at lower austenitization temperatures there is a large number of smaller carbides in the matrix and at higher temperatures we have a smaller number of carbides, which are larger. This results from the dissolution of smaller carbides and the growth of larger carbides (Ostwald ripening). The hardening speed of the roll affects the shape of the carbides. At a lower speed there is an oversaturation of the base or matrix, which affects the shape of the carbides – the carbides are thus more round. At a higher speed, however, carbides do not have as much time for the spheroidization and are thus more polygonal.
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