Ultrafast Granularization of Lath-like Bainite in FeNiC Alloys During Isothermal Holding

Meriem Ben Haj Slama (1, 2, 3) , Sébastien Allain (1) , Nathalie Gey (2, 3) , Lionel Germain (2, 3) , Kangying Zhu (4)

1 IJL - Institut Jean Lamour
2 Labex DAMAS
3 LEM3 - Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux
4 ArcelorMittal Maizières Research SA

Evidences of a fast and unexpected lath-like bainite «granularisation» during isothermal holdings will be reported. The phenomenon is characterized by improved angular resolution EBSD and TEM, and is observed in a Fe5Ni0.13C alloy transformed at 380°C (above Ms) after an austenitic soaking. The granularisation process starts once the initial lath bainitic transformation is over (lower and upper bainites) after 1 min and is characterized by an evolution of the ferrite matrix morphology and microtexture and by a carbide ripening process. During subsequent holdings (typically 30 min), variant coalesced zones develop and rapidly grow within paquets, at the expense of highly misoriented laths (60°) .The resultant low misorientation angle boundaries then progressively recover and carbide films precipitate on former packet boundaries. This explains the mechanical properties decrease. The associated driving forces will be discussed. This tempering mechanism occurring with slower kinetics in more conventional FeNiMnC alloys could contribute to bainite classification.

Domaines: Matériaux

Meriem Ben Haj Slama, Sébastien Allain, Nathalie Gey, Lionel Germain, Kangying Zhu. Ultrafast Granularization of Lath-like Bainite in FeNiC Alloys During Isothermal Holding. PTM 2015 - International conference on solid-solid phase transformations in inorganic materials, Jun 2015, Whistler, Canada. ⟨hal-01513122⟩