Formation and control of large-size TiN in GCr15SiMn bearing steel
LU Chun-guang1, ZHANG Guo-lei2, CHENG Guo-guang2, MIAO Hong-sheng1, ZHANG Xu1
1. Research and Development Department, Xining Special Steel Group, Co., Ltd., Xining 810005, Qinghai, China; 2. State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China
Abstract：Based on the production of GCr15SiMn bearing steel by EAF→LF→VD→IC process route in Xining Special Steel Plant, the characteristics and quantity of large-size TiN inclusions in ingot are studied by means of mineral dissociation analyzer, automatic inclusion analysis system, chemical analysis, X-ray fluorescence spectrometer and thermodynamic calculation, and the reasons for the increase of Ti content in steel during smelting stage are analyzed, the improved process is put forward. By the thermodynamic calculation of residual Ti and N content in bearing steel, it was found that TiN were mainly precipitated and grown up during solidification, and reducing Ti content in refining process was the main approach to control the formation of TiN. By the analysis of the change of Ti content during the original process, the results show that the titanium increase mainly occurs in the process from EAF tapping to the end of LF, in which 52% of total titanium increase comes from slag. In order to prevent titanium in slag from entering molten steel, the effects of Al content and CaO content in slag on LTi are discussed and the best equilibrium slag composition is predicted with the help of the previously established thermodynamic model of LTi between equilibrium slag CaO-SiO2-MgO-FeO-Al2O3-SiO2-TiO2 and molten steel. The results show that the LTi between slag and steel can be increased and the titanium content in molten steel can be reduced by appropriately reducing the Al content and CaO content; When the Al content is 0.015%-0.025% and the mass perceng of CaO is 50%-55%, the optimum composition range of other slag components (mass percent)is 18%-24% Al2O3 and 12%-17% SiO2. Besides, the relationship between the amount of slag from EAF and the titanium content at the end of LF under different LTiconditions is further described quantitatively. Finally, the amount of roughing-slag of EAF, Al content and slag composition in LF refining process were adjusted, and the improved process tests were carried out. Result showed that Ti content at the final point of smelting could be controlled below 0.002 0%, and the average TiN density of ingot could be reduced from 2.09/mm2 to 0.73/mm2, and the size of TiN is almost no more than 10 μm.
卢春光, 张国磊, 成国光, 苗红生, 张旭. GCr15SiMn轴承钢中大尺寸TiN生成与控制[J]. 钢铁, 2022, 57(12): 88-96.
LU Chun-guang, ZHANG Guo-lei, CHENG Guo-guang, MIAO Hong-sheng, ZHANG Xu. Formation and control of large-size TiN in GCr15SiMn bearing steel[J]. Iron and Steel, 2022, 57(12): 88-96.
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2022, Vol. 57 
