For the present work, the thermal fatigue resistance of CG HSS cast iron samples, typically used in the production of hot working rollers, was tested in the laboratory on the Gleeble 1500D thermo-mechanical simulator. The microstructure of the samples was characterized using JEOL JSM 6500F and ThermoFisher Scientific Vacuum Quattro S electron microscopes. The microstructure consisted of matrix, eutectic carbides (based on Fe (ca 68 wt. %)), carbides based on the highest value for Nb (ca 64 - 68 wt. %), V and Mo, carbides based on the highest value for V (ca 31 - 32 wt. %), Nb, Mo and graphites. The tests were performed at maximum test temperatures of 500 °C and 650 °C, respectively, and interrupted at 250, 750, 2500 and 6000 cycles. The length of cracks on samples created by cooling water temperature gradient was measured with an optical microscope. The resistance to thermal fatigue of CG HSS cast iron was quntified by calculating the mean length of all cracks, the mean length of the seven longest cracks, the longest crack, the crack density, and the area under linked cracks. Oxidation of eutectics, graphite areas, and other carbides was much more pronounced at higher test temperatures, i. e., 650 °C, than at a lower test temperature, i. e., 500 °C. The carbides based on the highest Nb value, as well as the highest V values, demonstrated greater brittleness and a greater tendency to oxidation. Cracks were predominantly initiated on areas with thicker carbides where pronounced cracking was observed, while crack growth was primarily associated with the carbide and graphite pathways.
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