QD08钢中Ds类夹杂物形成原因及控制

Formation reason and control of Ds inclusions in QD08 steel

QD08钢因其特殊的工作环境,要求具有较高的抗疲劳特性,而Ds类夹杂物是削弱QD08钢抗疲劳性能的主要原因。为了探究Ds类夹杂物的形成原因及调控方法,解决Ds类夹杂物超标问题,对该钢种炼钢-精炼-连铸全流程进行取样分析。分析结果表明,影响QD08钢疲劳性能的Ds类夹杂物主要成分为CaS-Al_(2)O_(3)-MgO-CaO,其尺寸在15~30μm范围内波动,主要在LF精炼钙处理操作后开始出现。QD08钢中Ds类夹杂物是以钙镁铝酸盐为核心骨架,外围包裹CaS而形成的。结合夹杂物的成分分布,确定了钢中钙含量高不利于QD08钢中Ds类夹杂物的控制,被改性后的夹杂物熔点低,与钢液润湿性强而难以穿过钢渣界面进入到渣中,且夹杂物在钢液中易聚合长大,造成夹杂物尺寸的增加,为Ds类夹杂物的形成提供了条件。提出在精炼环节采用高氧化钙溶解度精炼渣和微钙处理工艺优化方案,并进行了工业验证试验。通过微钙处理保证了必要的夹杂物改性,可防止水口结瘤,配合减小中间包液面的波动,控制合适的拉坯速度,可避免钢包下渣和卷渣现象的发生。控制更多的夹杂物成分分布在非液相区,抑制了夹杂物的碰撞长大,使得Ds类夹杂物等级降低。试验结果表明,QD08钢中影响其疲劳性能的Ds类夹杂物得到了控制,初检合格率由93.6%提高至98.0%,为企业带来了直接的经济利益。

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-Al_(2)O_(3)-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.