Deoxygenated alloying inclusions in Fe-Mn-Al-C low density steel
CAO Lei1, GUO Yuhang1, WANG Guocheng1,2, SHANG Deli3
1. School of Materials and Metallurgy, University of Science and Technology Liaoning, Anshan 114051, Liaoning, China; 2. Key Laboratory of Metallurgy Engineering Liaoning Province, Anshan 114051, Liaoning, China; 3. Iron and Steel Research Institutes of Ansteel Group Corporation, Anshan 114009, Liaoning, China
Abstract:In order to study the formation and mechanism of inclusions in Fe-Mn-Al-C low density steel during deoxygenation alloying, Si, Mn, and Al were used for deoxygenation alloying of the steel. Inclusions in Fe-Mn-Al-C low density steel samples were observed by field emission scanning electron microscopy combined with automatic inclusion analysis system. The results show that the inclusions in Fe-Mn-Al-C low density steel are classified into six types, single particle Al2O3 inclusion, single particle MnS inclusion, single particle AlN inclusion, Al2O3-MnS composite inclusion, AlN-MnS composite inclusion and Al2O3-AlN-MnS composite inclusion. The number of single particle Al2O3, MnS, and AlN inclusions is relatively large, and the size of the inclusions is mainly less than 5 μm. Thermodynamic calculations have found that Al2O3 forms during deoxygenation alloying, AlN begins to precipitate when the solid fraction is 0.844, while MnS begins to precipitate in the solid-phase steel after complete solidification. The calculation of two-dimensional lattice mismatch between different inclusions shows that the mismatch degrees of MnS (110)/Al2O3 (001), AlN (001)/Al2O3 (001), and MnS (100)/AlN (100) are 8.41%, 11.66%, and 8.94%, respectively, indicating that Al2O3 and AlN can provide heterogeneous nucleation sites for the nucleation of MnS, and Al2O3 can also provide heterogeneous nucleation sites for the nucleation of AlN. FactSage 8.2 thermodynamic software calculation is found that when cooled from 1 873 K to 373 K, the mass fractions of Al2O3, AlN, and MnS inclusions are 0.129%, 0.017%, and 0.615%, respectively. The study results can provide theoretical guidance for the formation of inclusions in Fe-Mn-Al-C low density steel during deoxygenated alloying.
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