THE ASSESSMENT OF CHANGES OF THE STRUCTURE OF DUCTILE CAST IRON DEPENDING ON THE TIME AND TEMPERATURE OF THE METALLURGIC PROCESS

The results of technological tests (chemical composition, solidification curves, microstructure) of ductile cast iron smelting in the Foundry Research Institute in an induction furnace. In the case of crystallization of spheroidal graphite no long fixed temperature stop associated with the crystallization of the structure was observed, and then rapid reduction of the temperature at the end of solidification process, with a clearly visible thermal inflection point during eutectic and graphite crystallization. The temperature, after reaching the maximum, slowly but steadily declined, and the inflection point of the end of the crystallization was difficult to determine. In the case when graphite precipitated in the vermicular form the image of the cooling curve was of indirect nature. In fact there was a stop with fixed temperature but it was shorter than in the case of scale graphite occurrence and there was no clear inflection point observed after the end of solidification. Suspending the molten metal in the induction furnace during the test resulted in a significant loss of magnesium assimilated in the process of spheroidization. The research was carried out on behalf of Fabryka Armatur JAFAR SA under the Innovative Economy Operational Programme 2007-2013, project: "Implementation of innovative technology of valve manufacturing in Fabryka Armatur JAFAR SA".

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