| The technology of oxide metallurgy has been proposed to utilize the positive effect of fine oxide to refine steel grain. Due to the perspective prospect, this technology has been a subject of intense study. Besides Ti-bearing inclusion, Mg-bearing oxide has recently attracted much attention due to its special properties. However, the mechanism of its induced intragranular acicular ferrites(IAF) nucleation effect is still under discussion.In this thesis, the relationship between inclusion feature and its induced nucleation effect has been explored by SEM(JSM-6510LV) and EDS(INCA Feature X-Max 20). To conduct further detailed analysis of inclusions, the line scanning and mapping functions of EDS are applied to reveal the elements distribution in inclusion. Moreover, Feature software of EDS is utilized to automatically analyze a large number of inclusions, and character their statistical features.The main conclusions are presented as follows:First, trace magnesium treatment was carried out in low carbon steel under laboratory conditions. The features of inclusion and microstructure were studied, and compared with non-treated sample. After etching, the typical microstructure of IAF is observed in Mg-treated sample, which is due to the nucleation effect induced by Mg-Al-O complex inclusions. This phenomenon can be explained by the absorption of Mn due to the magnesium vacancy in MgAl2O4.Second, phenomena of IAF nucleation induced by different kinds of inclusion(Mg-Al-O, Ti-Mg-Al-O, Ti-Al-O) were studied discussed, respectively. In all samples, line EDS analysis hints that Mn-depletion zone exists in steel matrix, where is adjacent to the inclusion. Based on the theoretical analysis of inclusion composition complexity, these phenomena can be explained by the absorption of Mn due to the cation vacancy in inclusion.Third, through statistical analysis of SEM images for microstructure, the probabilistic nature of inducing nucleation effect is revealed. |
PDF Full Text Request