Effect of LF soft bubbling time on oxide inclusions in Si-killed spring steel
MENG Yao-qing1,2, LI Jian-li1,2, ZHU Hang-yu1,2, WANG Kun-peng3
1. Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Hubei Provincial Key Laboratory of New Processes of Ironmaking and Steelmaking, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 3. Technology Center, Zenith Steel Group Co., Ltd., Changzhou 213011, Jiangsu, China
Abstract：In order to ensure the cleanliness of molten steel, the long-time soft bubbling during LF refining process is often chosen for some Si-Mn deoxidized special steels, resulting in increased energy consumption in the process. Based on the industrial tests, the effects of LF soft bubbling time on the composition and number density of inclusions in Si-killed spring steel bloom were investigated through a scanning electron microscope (FEI Explorer 4), and the maximum size of inclusions in the crossing section of wire rods collected from the LF process with different soft-bubbling times was compared and evaluated by the extreme-value statistical method. The results showed that for the LF processes with two soft-bubbling time, 10 min and 40 min, the compositions of oxide inclusions larger than 5 μm in the blooms were close, and both in the low-melting point region at the eutectic zone of pseudo-wollastonite, anorthite, and gehlenite of CaO-SiO2-Al2O3 phase diagram. The proportion of oxide inclusions falling into the low-melting point region in the 10 min soft-blowing process was higher than that in the 40 min soft-blowing process. The number densities of oxide inclusions with size larger than 5 μm were 11.70 /100 mm2 and 14.59 /100 mm2 respectively in the blooms adopted 10 min and 40 min soft-bubbling processes. Meanwhile, the number densities of oxide inclusions with size above 15 μm were 0.53 /100 mm2 and 1.65 /100 mm2, respectively. The number density of large oxide inclusions in the bloom of 10 min soft-bubbling process was slightly lower than that of 40 min soft-bubbling process. When the predicted area was 30 000 mm2, the maximum sizes of oxide inclusion in the cross sections of wire rods were 27.1 μm and 28.1 μm respectively, and there was no significant difference of them. The low-melting point CaO-SiO2-Al2O3 inclusions with large size in Si-Mn killed steel mainly come from the emulsification of ladle slag, which had a small interface-contact angle with molten steel and argon bubble and was difficult to be removed by argon floating. It is suggested that the soft-bubbling time during LF refining should be controlled in a short time for Si-Mn deoxidized steel.
孟耀青, 李建立, 朱航宇, 王昆鹏. LF软吹时间对硅脱氧弹簧钢氧化物夹杂控制影响[J]. 钢铁, 2022, 57(5): 48-54.
MENG Yao-qing, LI Jian-li, ZHU Hang-yu, WANG Kun-peng. Effect of LF soft bubbling time on oxide inclusions in Si-killed spring steel[J]. Iron and Steel, 2022, 57(5): 48-54.
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2022, Vol. 57 
