Three-dimensional morphology of non-metallic inclusions and the source analysis of wrapped non-inclusion particles
ZHANG Xue-wei1, ZHANG Li-feng1, YANG Wen1, WANG Yi1, DONG Yuan-chi2
1.Beijing Key Laboratory of Green Recycling and Extraction of Metals GREM, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China; 2.School of Metallurgical Engineering, Anhui University of Technology, Maanshan 243002, China
Abstract：The separation and extraction of non-metallic inclusions in steel should solve the interference problems of external factors. The accurate judgment of source (whether from steel or not) is the key point for the detection and characterization of inclusions. The heavy rail steel U75V was selected for analysis under laboratory conditions. The non-metallic inclusions in steel were separated and extracted by acid dissolution method and non-aqueous electrolysis method. The morphology and composition of inclusions were systemically analyzed and characterized by scanning electron microscope (SEM). The results showed that the morphology and composition of acid-resistant inclusions could be effectively acquired by acid dissolution method equipped with an electromagnetic stirring device. The optimized solution medium was hydrochloric acid (1+1). The acid-resistant and acid-nonresistant non-metallic inclusions in micro and nano-scale could be obtained by non-aqueous electrolysis method. The electrolysis time was controlled at 8-10 h. Meanwhile, the analytical results of U75V steel by acid dissolution method and electrolysis method indicated that large-size and irregular particles existed in inclusions. The analysis revealed that these particles belonged to foreign particles, which were defined as non-inclusions. They were mainly from air, tap water, drying oven and electrolysis device, etc. Their chemical composition was mainly composed of MgO, CaO, SiO2 and Al2O3, which were closed to that of oxide inclusions in steel. As a consequence, it may cause inaccurate guidance for the control strategy of inclusions during steelmaking. Therefore, the protective operation should be carried out during the separation and extraction process of inclusions in steel to avoid the interference of adverse factors. Thus, the detailed information such as three-dimensional morphology, size and chemical composition of inclusions in steel could be accurately obtained, which could provide effective support for process improvement or experimental research.
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