International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Structural changes on the surface of R260Mn grade rails, developed during wheel/rail contact were investigated by optical microscopy, electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD) in scanning electron microscope (SEM) and transmission electron microscopy (TEM) The microstructures of the heavily deformed surface layer known as white etching layer (WEL) and the deformed under layer were characterized in different length scales. Ferrite grain fragmentations and grain alignment in normal direction, (perpendicular to traffic direction) are characterized by all applied methods. Substructures, having misorientations lower than 5°, are identified by analysing the local misorientation maps (kernel average misorientation (KAM)). Retained austenite was detected in the WEL by XRD, EBSD and TKD. Detection of retained austenite and ultrafine grain structure were considered as an indication for mixed mechanism of formation of the WEL where both martensitic transformation and severe plastic deformation take place.

The texture evolution in pipeline steel is studied as a function of the thermo-mechanical processing parameters –rolling tem- perature and cooling rate after the finish rolling stage carried out with equal rolling reduction per pass.. The austenite recrystallization and grain growth during thermo-mechanical control processing (TMCP) of a pipeline steel grade are described and analysed in terms of precipi- tation state progress. Two stage controlled rolling (roughing and finishing) was carried out on a laboratory rolling mill for a set of complet- ed and interrupted schedules. Subsequent to rolling, two different cooling routes were used water quenching and accelerated water cooling (ACC) together with coiling simulation. From the combination of transmission electron microscopy (TEM) observations, detailed texture analysis and inductively coupled plasma-mass spectroscopy (ICPMS) precipitates quantification, consistent correlations between precipita- tion state and microstructure at every stage of TMCP can be recognized. The formation of specific transformation textures was explained via appropriate texture models that describe both formation of transformation and recrystallization textures in the austenite.

This study aims to optimize the heat treatment of tool steel 75Cr1 which is used for heavy loaded elements in transmissions. A salt bath was used to quench and temper the steel at different temperatures. Mechanical tests and microstructural characterization were done to define the heat treatment parameters corresponding to the optimal performance of the elements. Optical microscopy, electron back scatter diffraction and x-ray diffraction were used to characterize the microstructure, while tensile tests and toughness tests were employed to determine the mechanical properties after different heat treatments. It was found that the yield strength decreases with increasing annealing temperature and that the toughness decreases with increasing annealing time and temperature. The changes of the mechanical properties are discussed in relation with the thermal treatment and the corresponding microstructures.