1、内蒙古科技大学设计说明书 1 内 蒙 古 科 技 大 学 毕 业 设 计 外 文 翻 译 专 业： 冶金工程 班 级： 冶金一班 学 号： 0868100211 姓 名： 包春钢 导 教： 赵永旺 内蒙古科技大学设计说明书 2 Basic oxygen furnace based steel-making processes and cleanliness control at Baosteel L. Zhang*1, J. Zhi2, F. Mei2, L. Zhu2, X. Jiang2, J. Shen2, J. Cui2, K. Cai3 and B. G. Thomas4 Optic
2、al microscopy, total oxygen measurements and slime tests have been conducted to quantify the size distribution and amount of inclusions at various processing steps during basic oxygen furnace (BOF) based steel production at Baosteel. The effects on steel cleanliness of specific operational improveme
3、nts during steel refining and continuous casting have been investigated. Such improvements to these processes and the resulting level of steel cleanliness at Baosteel are summarised in the present paper. Ladle slag reduction lowers FeO + MnO in the slag to below 5%, decreasing steel reoxidation by t
4、he slag. Calcium treatment by CaSi wire injection during ladle furnace (LF) refining is used to modify inclusions . Slag detection is employed at the ladle bottom during continuous casting. Flow control devices, CaO containing filters and high CaO based basic powder with CaO/Si024 are used in the tu
5、ndish to remove more inclusions. With this BOF based steelmaking process, impurity levels can be controlled to achieve-total oxygen (TO)16 ppm, S5 ppm, P35 ppm, N29 ppm, H1 ppm in line pipe steels, and C16 ppm, TO19 ppm, N15 ppm in interstitial free (IF) steels. Keywords: Clean steel, Inclusions, Im
6、purity elements, Interstitial free steel, Line pipe steel Introduction The importance of clean steel in terras of product quality is increasingly being recognised. Clean steel requires control of the size distribution, morphology and composition of non-metallic oxide inclusions in addition to the am
7、ount. Furthermore, sulphur, phosphorus, hydrogen, nitrogen and even carbon1,2 should also be controlled to improve the steel properties. For example, ,formability, ductility and fatigue strength worsen with increasing sulphide and oxide inclusion contents. Lowering the carbon and nitrogen enhances s
8、train 内蒙古科技大学设计说明书 3 aging and increases ductility and toughness. Hardenability and resistance to temper embrittlement can be enhanced by reducing phosphorus. The definition of clean steel varies with the steel grade and its end use. For example, interstitial free (IF) steel requires both carbon and
9、 nitrogen to be 30 ppm； line pipe steel requires sulphur, phosphorus and total oxygen (TO) all to be 30 ppm， low hydrogen, low nitrogen and suitable Ca/S and bearing steel requires the total oxygen to be less than 10 ppm.3 In addition, many applications restrict the maximum size of inclusions 3,4 ,
10、so the size distribution of inclusions is also important. Baoshan Iron & Steel Co., Ltd (Baosteel) is currently the largest steel company in China. Its annual steel production was 115 million tonnes in 2003, 119 million tonnes in 2004 and 14.0 million tonnes in 2005. With regard to the basic oxygen
11、furnace (BOF) based steelmaking route, there are three 300 t and two 250 t BOFs； several steel refining units, including one CAS-OB unit (controlled argon stirring-oxygen blow), two RH (Ruhrstahl-Heraeus) degassers and one ladle furnace (LF). Since 1990, efforts to improve steel cleanliness have foc
12、used on developing steelmaking practices to lower TO, N, S, P, H and C levels to achieve low carbon aluminium killed (LCAK) steel. For LCAK steel and IF steel, the production process is BOF RH continuous casting (CC), and for line pipe steel, the process is BOF RH LF CC. Experimental method and exam
13、ination of inclusions in steel Experimental methods Ladle steel samples were taken 500-600 mm below the top slag in the ladle, tundish steel samples from 300 mm above its outlet and mould steel samples from 150 mm below the meniscus and 300 mm away from the submerged entry nozzle (SEN) outports. The
14、 sampler was a cylindrical steel cup with a cone shaped copper cover to protect it from slag entrainment during immersion. Attached to a long bar, the sampler was immersed deep into the molten steel, where the copper melted and the cup was filled. Small steel samples , 80mm in length and 30mm in diameter, were machined into 5 (dia.) x 5 mm cylinders for TO and nitrogen analysis, and 20 (dia.) 15 mm cylinders for microscope examination. The steel powders resulting from machining were used for analysis of the carbon, phosphorus and
