Formation reason and control of Ds inclusions in QD08 steel
SONG Zhao-qi1, LIU Wei1, YANG Shu-feng1, LI Jing-she1, CHEN Yong-feng2, ZUO Xiao-tan2
1. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China; 2. Wuhu Xinxing Casting Pipe Co., Ltd., Wuhu 241000, Anhui, China
Abstract：QD08 steel requires high fatigue resistance due to its special working environment, and Ds inclusions are the main reason for weakening the fatigue resistance of QD08 steel. In order to explore the reasons for the formation of Ds inclusions and control methods, and solve the problem of excessive Ds inclusions, the whole process of steelmaking, refining and continuous casting of this steel grade was sampled and analyzed. The analysis results show that the main component of Ds inclusions that affect the fatigue performance of QD08 steel is CaS-Al2O3-MgO-CaO, and its size fluctuates in the range of 15-30 μm, which mainly begin to appear after the LF refining calcium treatment operation. The Ds inclusions in QD08 steel are formed by using calcium magnesium aluminate as the core framework and wrapping CaS on the periphery. Combined with the composition distribution of inclusions, it is determined that the high calcium content in steel is not conducive to the control of Ds inclusions in QD08 steel. The modified inclusions have a low melting point, and the inclusions have strong wettability with molten steel, making inclusions difficult pass through the steel slag interface into the refined slag. In addition, the inclusions are easy to aggregate and grow in the molten steel, resulting in an increase in the size of the inclusions, which provides conditions for the formation of Ds-type inclusions. The optimization plan for the refining slag with high solubility of calcium oxide and micro-calcium treatment in the refining process was proposed, and industrial verification tests were carried out. The micro-calcium treatment ensures the necessary inclusion modification, prevents the nozzle nodules, cooperates with reducing the fluctuation of the tundish liquid level, controls the appropriate drawing speed, avoids the slag leaving from the ladle, and avoids the occurrence of slag entrapment. The process controls more inclusions to be distributed in the non-liquid zone, inhibits the collision and growth of inclusions, and reduces the level of Ds inclusions. The test results show that the Ds inclusions in QD08 steel that affect its fatigue performance have been controlled, and the initial inspection pass rate has been increased from 93.6% to 98.0%, which has brought direct economic benefits to the enterprise.
宋朝琦, 刘威, 杨树峰, 李京社, 陈永峰, 左小坦. QD08钢中Ds类夹杂物形成原因及控制[J]. 钢铁, 2021, 56(12): 68-74.
SONG Zhao-qi, LIU Wei, YANG Shu-feng, LI Jing-she, CHEN Yong-feng, ZUO Xiao-tan. Formation reason and control of Ds inclusions in QD08 steel[J]. Iron and Steel, 2021, 56(12): 68-74.
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2021, Vol. 56 
