Abstract
A new approach for pre-dispersing MgO nanoparticles and adding them to molten steel during continuous casting operations was established. The influence of different mass fractions of MgO nanoparticles on inclusion characteristics, steel microstructure, and the ability of inclusions to induce acicular ferrite (AF) formation, was investigated. The results revealed that after adding different mass fractions of nanoparticles, the majority of inclusions contained MgO-Al2O3, and the inclusion size was considerably refined. These inclusions promoted AF formation, and with increasing inclusion size from 1.0 to 1.8 μm, the proportion of AF progressively increased. The ability of inclusions to induce AF was greatly reduced when the inclusion size reached 7.0 μm. This was primarily due to the relationship between the ferrite nucleation rate and inclusion size. It was also found that the size of inclusions that functioned as pinning particles was larger than that of inclusions that served as AF nucleation cores. When the mass fraction of MgO nanoparticles reached 0.05 pct, the degree of interlocking of AF within the microstructure of billet specimens was maximized and this was associated with optimal values for strength and impact properties.
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Abbreviations
- AF:
-
Acicular ferrite
- BF:
-
Banded ferrite
- EAM:
-
External addition method
- EDS:
-
Energy-dispersive spectrometry
- f :
-
Volume fraction of particles
- IAF:
-
Intragranular acicular ferrite
- IPM:
-
Internal precipitation method
- N V :
-
Quantity of inclusions per unit volume
- PAGB:
-
Primary austenite grain boundaries
- PF:
-
Polygonal ferrite
- r :
-
Radius of the pinning particles
- R :
-
Zener limit
- R*:
-
A non-dimensional parameter which is proportional to the radius of curvature of the inclusions
- R I :
-
Radius of curvature of the inclusions
- r C :
-
Critical radius of inclusions that will nucleate ferrite
- SEM:
-
Scanning electron microscopy
- θ :
-
Contact angle between ferrites and inclusions
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Acknowledgments
This research is supported by the National Science Foundation of China (No. 51474076 and 51304016) and open fund of State Key Laboratory of Advanced Metallurgy (No.KF14-02 and KF14-06). Appreciation is also expressed to the Natural Sciences and Engineering Research Council of Canada for support of steel-related research at the University of Toronto.
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Manuscript submitted August 8, 2015.
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Gao, X., Yang, S., Li, J. et al. Effects of MgO Nanoparticle Additions on the Structure and Mechanical Properties of Continuously Cast Steel Billets. Metall Mater Trans A 47, 461–470 (2016). https://doi.org/10.1007/s11661-015-3237-1
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DOI: https://doi.org/10.1007/s11661-015-3237-1