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Formation des microstructures dans la fonte à graphite spheroïdal aux premiers instants de la solidification

Abstract : The thermal conditions and the treatment of the liquid metal for centrifugal casting of pipes lead to the solidification of the melt in the form of spheroidal graphite (SG) iron throughout the thickness. However it is sometimes observed zones that are solidified within the white mode (eutectic austenite / cementite) mainly in the skin of the product. These areas lead to differences which could be problematic. Further characterization of the microstructure of pipes shows that competition between the nucleation and growth of stable and metastable eutectic growth exists from the beginning of solidification. To clarify the thermal conditions of this competition an experimental device has been used. Liquid metal droplet fall on a cold substrate. Rapid directionnal solidification occurs and the temperature evolution of the lower surface of the droplet is recorded during the very first moment of solidification (< 200 ms). Characterization of droplet microstructures obtained in as-cast state and after heat treatment showed that the device is able to froze the solidified microstructure in an earlier stage of formation than in the as cast pipe. A physical model describing the first instants of the solidification under very high thermal gradient of a cast iron which is inoculated and treated with Mg is presented, taking into account the kinetics of nucleation and growth of graphite nodules in competition with the solidification of the metastable eutectic. The comparison between the calcluated results and microstructural characterizations allows to specify microstructures devlopment scenarios by decoupling the influence of the thermal gradient and solidification rate
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https://hal.univ-lorraine.fr/tel-01749479
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  • HAL Id : tel-01749479, version 1

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Shuyan Wang. Formation des microstructures dans la fonte à graphite spheroïdal aux premiers instants de la solidification. Alimentation et Nutrition. Université de Lorraine, 2012. Français. ⟨NNT : 2012LORR0338⟩. ⟨tel-01749479⟩

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