Abstract
Owing to the insufficient converter heat, IF steel is produced via the BOF–LF–RH–CC process in Pangang Group Xichang Steel and Vanadium Co., Ltd. To clarify the evolution of inclusions and the control strategy to improve the cleanliness of molten steel in Ti-bearing IF steel produced via the long process, scanning electron microscopy with energy spectroscopy analysis and automatic scanning electron microscopy were employed to analyze the number, size, type and morphology of inclusions in IF steel from RH to tundish. The results show that the characteristics of inclusions are similar in two heats during RH treatment. In the tundish sample of Heat 2, the number density (ND) and area fraction (AF) of Al2O3 and Al2O3·TiOx inclusions increase significantly, and the size of Al2O3 inclusions decreases obviously, which is closely related to the serious reoxidation of molten steel caused by the slag with high oxidability during the holding process. Meanwhile, a new method of determining the number of cluster inclusions is used to evaluate the cleanliness of IF steel in this paper, and the obtained number of inclusion clusters is consistent with the trend of ND and AF of inclusions. The effects of reoxidation on the morphology, number and other indexes of Al2O3 and Al2O3·TiOx inclusions are discussed in detail, and there are two ways of forming Al2O3·TiOx inclusions in the case of serious reoxidation. To weaken the reoxidation process and enhance the cleanliness of IF steel produced via the long process, reducing the oxygen content in molten steel before Al deoxidation, minimizing the holding time and reducing the oxidability of slag after RH are helpful.
Highlights
Ti-bearing IF steel is widely used in automotive, home appliances, electronics and other fields due to its good deep-drawing performance
Atotal where ND is the number density of inclusions, mm−2; Atotal is the sample detection area, mm2; n is the number of detected inclusions on the area of Atotal; AF is the area fraction of inclusions, 10−6; and Ainclusion is the total area of detected inclusions, μm2
The ND of Al2O3 inclusions in molten steel is over 35 mm−2 within 3 min after Al addition, and the average size of Al2O3 inclusions is about 2.3 μm
Summary
Ti-bearing IF steel is widely used in automotive, home appliances, electronics and other fields due to its good deep-drawing performance. With the market’s increasing requirements for the surface and internal quality of final products, the demand for highquality IF steel is increasing [1,2]. The performance of IF steel is greatly affected by the type, number and size distribution of nonmetallic inclusions [3–6]. Engine failure caused by nonmetallic inclusions of tens of microns is a typical problem in the automotive industry [7,8]. Clogging of the submerged entry nozzle is a common problem in the steelmaking process because of the presence of Ti [9–12]. It is important to enhance the potential for inclusion removal from molten steel during RH and tundish processes
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