Formation mechanism of CaO-Al2O3-TiOx+TiN system inclusions in Ti-bearing gear steel
HAO Guang-yu1,2, YUAN Kang1,2, GAO Jing1,2, DENG Zhi-yin1,2, ZHU Miao-yong1,2
1. Key Laboratory for Ecological Metallurgy of Multimetallic Mineral (Ministry of Education), Northeastern University, Shenyang 110819, Liaoning, China; 2. School of Metallurgy, Northeastern University, Shenyang 110819, Liaoning, China
Abstract：Industrial and laboratory experiments were carried out to investigate the formation mechanism of a special kind of complex inclusions (TiN surrounded by CaO-Al2O3-TiOx) in 20CrMnTi gear steel, and thermodynamic calculations were also conducted to check the possibility of the formation of TiN by the dissolved elements in the liquid steel. It is found that Ti-Fe alloy has poor cleanliness and contains many Al2O3 and TiN inclusions. At the steelmaking temperature, the reaction of dissolved Ti and N in steel to form TiN is thermodynamically impossible. The TiN core of the complex inclusions cannot be generated by the direct reaction between dissolved Ti and N in the steel but should be sourced from the Ti-Fe alloy. When the liquid CaO-Al2O3-TiOx inclusions collide with the undissolved TiN, TiN inclusions would be wrapped by the liquid inclusions, thus forming larger CaO-Al2O3-TiOx inclusions with a TiN core inside. Ti-Fe alloys with lower nitrogen content are suggested to control these inclusions.
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2020, Vol. 55 
