Effect of Mg-Al Spinel Solid Solution Composition on Precipitation Behavior of TiN
PANG Zongxu1,2, ZHU Rong1,2, CHEN Peidun1,3, WANG Junhai1,3
1 School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083; 2 Beijing Key Laboratory of Special Melting and Preparation of High-end Metals, Beijing 100083; 3 Shandong Taishan Steel Group Co. Ltd., Laiwu 271100
Abstract: Through the experiment of slag/steel reaction equilibrium on 2205 duplex stainless steel, inclusions in MgO-Al2O3 binary solid solution were obtained with different slag compositions. When the reaction reached the equilibrium, the new complex inclusion of MgO-Al2O3 solid solution combined with TiN would further form if adding 0.05% Ti to the steel. After water quenching, the inclusions were analyzed by SEM, and samples were electrolyzed by oxalic acid with content of 10%. And then grain morphology and size of δ ferrite was compared to that of as-cast microstructure without Ti. The experiment results showed that the precipitation quantity increased with the increase of Al2O3 proportion in MgO-Al2O3 solid solution while the grain of as-cast δ ferrite was obviously refined. It was found that TiN precipitated rarely out of MgO-rich MgO-Al2O3 solid solution and MgO-Al2O3, and the grain refining effect of δ ferrite was not obvious. By thermodynamic calculation, heterogeneous nucleation theory and experimental result analysis, it was concluded that inclusion composition of MgO-Al2O3 binary solid solution was jointly determined by slag composition and activity of Mg and Al. The increase of Al2O3 content in MgO-Al2O3 solid solution contributed to the lattice distortion of MgO-Al2O3, which is closely associated with vacancy in the lattice. Because of the enrichment of vacancies, lattice constant e was uneven. And vacancies had changed the crystal field and caused the movement or transfer of O2-, which led to omission solid solution of spinel. It was the energy state changes of lattice that promoted the precipitation of Ti and N atoms on the surface of MgO-Al2O3 inclusion.
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2017, Vol. 31 
