Complex Microstructural Banding of Continuously Cooled Carbide-Free Bainitic Steels

Abstract:

Chemical segregation of alloying elements during solidification of steel grades leads to development of a banded microstructure, causing a degree of anisotropy that can be detrimental to the mechanical behavior under service conditions. It is well-known that the presence of strongly orientated martensite bands in carbide-free bainitic microstructures, associated to inhomogeneous Mn redistribution during solidification, leads to a remarkable deterioration in toughness in advanced high strength bainitic steels. In this study, while bands were clearly visible on light optical micrographs of continuously cooled carbide-free bainitic steels, scanning electron microscopy examination revealed only a gradual transition between matrix and bands, both with a granular bainitic structure. Electron backscatter diffraction was used to quantify the bainitic packet size and volume fraction of martensite/austenite constituent between and within the bands, after a process of optimization of the analysis settings in order to minimize the inherent difficulties linked to sub-micrometric and minority phase indexation. The quantitative microstructural results showed negligible morphological differences between bainitic structure bands and matrix, only solute segregation of Cr and Mo was detected by energy-dispersive X-ray spectroscopy within bands, which must be responsible for a stronger resistance against metallographic etching in those regions.

• Periodical: Materials Science Forum (Volumes 783-786)
• Pages: 980-985
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.783-786.980
• Online since: May 2014
• Authors: Lucia Morales-Rivas*, Hans Roelofs, Stephan Hasler, Carlos Garcia-Mateo, Francisca G. Caballero
• Keywords: Bainite, EBSD, EDS, Microstructural Banding

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