Anisotropic Ferrite Growth and Substructure Formation during Bainite Transformation in Fe-9Ni-C Alloys: In-Situ Measurement

Abstract

Growth kinetics of bainitic ferrite is re-examined in Fe-C-9%Ni alloys by taking the morphological anisotropy of bainitic ferrite due to crystallographic constraint in in-situ observation using confocal laser scanning microscopy. The true lengthening kinetics determined, after identifying crystallographic variants of bainitic ferrite in post-transformation EBSD measurement, is faster by a factor of about 4 than the apparent lengthening kinetics measured as a projection on the observed surface. The lengthening rate is mostly equal to or still slower than those predicted by carbon diffusion controlled kinetics. Variant pairing of bainitic ferrite belonging to the same Bain group occurred preferably in development of local substructure as previously reported in low-alloy low-carbon steels.