Influence of modification processes on inclusion properties of high strength low alloy steel
ZHANG Hong-yan1,2, TIAN Zhi-hong1, SHAO Xiao-jing1, LUAN Yi-kun3, DENG Xiao-xuan1, JI Chen-xi1
1. Research Institute of Technology, Shougang Group Co., Ltd., Beijing 100043, China; 2. Beijing Key Laboratoryof Green Recyclable Process for Iron and Steel Production Technology, Beijing 100043, China; 3. Shenyang National Laboratory of Materials Science, Institute of Metals, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China
Abstract：The influence of different inclusion modification processes (including unmodified, RE treatment and Ca treatment) on the inclusion characteristics of aluminum-killed high-strength low alloy steel was studied by the industrial 300 t ladle furnace. The results show that the inclusions were mainly irregular Al-Mg-Ca-O-S-Mn composed inclusion with high aluminium content. The inclusion density was the lowest (only 7.4 and 9.5/mm2), but the average size of the inclusions was more than 3 μm, and the number of large size inclusions not less than 20 μm was up to 0.1/mm2. The inclusions in steel plate sample by Re treated furnace are mainly spherical La-Ce-O-S with a small amount of Ca or Al. Although the maximum inclusion density is 32.5/mm2, the average inclusion size is the smallest (only 2.3 μm). No inclusions less than 20 μm were detected in one sample, and almost no large inclusion(≥20 μm) was detected in the other sample (only 0.01/mm2). The inclusions in the steel plate of the Ca treated furnace were almost spherical inclusions. The inclusions were mainly Ca-Al-S-O. Besides, partial inclusions may contain small amounts of Mg or Mn. And the number of inclusions is also large, about 30/mm2. The average size of inclusions is 2.7 μm, slightly larger than that of the rare earth treatment furnace, and basically there was no inclusion with size not less than 20 μm (0.01/mm2). The high temperature confocal microscopy tests show that the inclusion treated with rare earth and calcium is not easy to aggregate into large size inclusions at high temperature, while the alumina in the unmodified furnace is easy to aggregate into large size inclusions due to the high interface tension with liquid steel.The inclusions in the steel plate of the Ca treatment furnace were basically spherical inclusions. The inclusions were composed of CaS and calcium aluminate. And the number of inclusions was also large, about 30/mm2. The average size of inclusions was 2.7 μm, slightly larger than that of the RE treatment furnace, and basically there was no inclusion with size not less than 20 μm(0.01/mm2). The confocal laser scanning microscopy results showed that the inclusions treated with rare earth and calcium were not easy to aggregate into large sized inclusions at high temperature. Al2O3 in the unmodified furnace was easy to aggregate into large sized inclusions due to the high interface tension with liquid steel.
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2021, Vol. 31 
