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Advances in Materials Science and Engineering
Volume 2015, Article ID 378678, 6 pages
Research Article

The Mechanism of Intragranular Acicular Ferrite Nucleation Induced by Mg-Al-O Inclusions

School of Metallurgical Engineering, Anhui University of Technology, Maanshan, Anhui 243002, China

Received 6 May 2014; Accepted 12 January 2015

Academic Editor: Pavel Lejcek

Copyright © 2015 Kong Hui et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The features of inclusion and microstructure for carbon structural steel containing Mg-Al-O inclusions were studied through the scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS). It can be seen that, in Mg-Al-O inclusions, the elements of Mn, Si, and S coexist, and their central mole ratio of Mg/Al varies in a wide range. This value for most inclusions is larger than 0.5, which suggests the formation of solid solution between MgAl2O4 and MgO. After etching, the typical microstructure of intragranular acicular ferrites is observed, which is due to the nucleation effect induced by Mg-Al-O inclusions. From the SEM-EDS mapping images, it is found that the element of sulfur accumulates on the periphery of nucleation inclusion. Moreover, line EDS analysis hints that Mn-depletion zone (MDZ) exists in steel matrix, which is adjacent to the complex inclusion. Combined with the theoretical analysis, this phenomenon can be explained by the absorption of Mn due to the magnesium vacancy in MgAl2O4, and this MDZ promotes the nucleation of intragranular acicular ferrite. Through statistical analysis of SEM images for microstructure, the probabilistic nature of inducing nucleation effect is revealed. These results may be helpful to clarify the nature of oxide metallurgy.