Local strain analysis of the tertiary oxide scale formed on a hot-rolled steel strip via EBSD

Publication Type:
Journal Article
Citation:
Surface and Coatings Technology, 2015, 277 pp. 151 - 159
Issue Date:
2015-01-01
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© 2015 Elsevier B.V.. This work presents a fine microstructure and local misorientation study of various oxide phases in the tertiary oxide scale formed on a hot-rolled steel strip via electron back-scattering diffraction (EBSD). Local strain in individual grains of four phases, ferrite (α-Fe), wustite (FeO), magnetite (Fe < inf > 3 < /inf > O < inf > 4 < /inf > ) and hematite (α-Fe < inf > 2 < /inf > O < inf > 3 < /inf > ), has been systematically analysed. The results reveal that Fe < inf > 3 < /inf > O < inf > 4 < /inf > has a lower local strain than α-Fe < inf > 2 < /inf > O < inf > 3 < /inf > , in particular, on the surface and inner layers of the oxide scale. The multiphase oxides along the cracking or α-Fe < inf > 2 < /inf > O < inf > 3 < /inf > penetration generally develop a high local misorientation. Localised stain along the cracks demonstrates that the misorientation tends to be strong near grain boundaries. The high fraction of small Fe < inf > 3 < /inf > O < inf > 4 < /inf > grains accumulate at the oxide-substrate interface, which leads to a dramatic increase in the intensity of local stain. This variation is due mainly to the phase transformation among the oxide phases, i.e., the Fe < inf > 3 < /inf > O < inf > 4 < /inf > particles during their nucleation and growth. The combined action of stress relief and re-oxidisation is proposed to explain the formation of Fe < inf > 3 < /inf > O < inf > 4 < /inf > seam at the oxide-steel interface. The present study offers an intriguing insight into the deformation behaviour of the tertiary oxide scale formed on steels, and may help with understanding the stress-aided oxidation effect of metal alloys.
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