Effect of RH titanium adjustment time and pure circulation time on cleanliness of IF steel
WEN Han1, ZHOU Hai-chen2, LUO Yan-zhao2, HUANG Cai-de1, ZHAO Chang-liang1
1. Steelmaking Department, Shougang Jingtang United Iron and Steel Co., Ltd., Tangshan 063200, Hebei, China; 2. Technology Center, Shougang Jingtang United Iron and Steel Co., Ltd., Tangshan 063200, Hebei, China
Abstract:In order to further improve the efficiency of RH refining and better match with high-speed casting, the effects of titanium adjustment time and circulation time on inclusions in the RH refining of IF steel were studied. The results show that the T.O mass fraction in the liquid steel is less than 0.003 0% after 5 min of Al addition. The number density of inclusions has a minimum value after alloying for 4-5 min, then it changed less with increasing of circulation time. In the industrial practice of 300 t RH, the Al-Ti interval time of 2 min and circulation time of 5 min, or the Al-Ti interval time of 3 min and circulation time of 4 min can ensure that inclusions are fully floated and removed in the liquid steel, and the number density of inclusions was 0.7-0.8/mm2, which can realize the high efficiency of RH refining. When the Al-Ti interval time is more than 1 min and circulation time is more than 3 min, no inclusions larger than 50 μm are detected in the liquid steel. The RH vacuum treatment time of IF steel has been decreased to 20 min based on the above process optimization. After adding Al to the liquid steel, Al2O3 inclusions are mainly formed. After adding Ti-Fe alloying, [Ti] rich region forms in the liquid steel and [Ti] reduces Al2O3 to form Al-Ti oxides. With the diffusion of [Ti] in liquid steel and the formation of Al-Ti oxides, the [Al] in liquid steel reduces the Al-Ti oxides to form Al2O3. Finally, composite inclusions with Al-Ti oxide as the core and the outer layer wrapped by Al2O3 are formed.
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WEN Han, ZHOU Hai-chen, LUO Yan-zhao, HUANG Cai-de, ZHAO Chang-liang. Effect of RH titanium adjustment time and pure circulation time on cleanliness of IF steel[J]. China Metallurgy, 2022, 32(9): 45-51.
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