Q690钢LF精炼渣系优化及工业试验

Optimization and industrial testing of LF refining slag system for Q690 steel

为控制Q690钢中T[O]含量和夹杂物,提高钢的洁净度,寻求合适的精炼渣系,首先对原工艺精炼渣系及夹杂物控制状况进行调研,使用Aspex自动扫描电镜对钢中尺寸大于2μm的夹杂物的形貌、尺寸和成分进行检测分析,确定了钙处理时机;其次采用FactSage软件对精炼渣-钢液-夹杂物的平衡进行热力学计算,分析精炼渣组分对钢中夹杂物成分的影响,同时开展了实验室试验,基于试验结果和理论模型计算得到了1550℃和1600℃温度条件下Al_(2)O_(3)在CaO-Al_(2)O_(3)-SiO_(2)渣中的溶解速率云图;最后确定了合适的Q690钢精炼渣渣系,降低了原工艺渣系的钙铝比,优化后的渣系w(CaO)/w(Al_(2)O_(3))控制在1.8~2.0,碱度控制在5.0~7.0。工业试验结果表明,渣系优化后Q690钢在RH出站后钢中T[O]质量分数可降至7×10^(-6)以下,夹杂物由调研阶段的最大直径40~60μm降至10~20μm;钢中检测到的夹杂物面积分数、数密度和最大直径显著降低,铸坯钢样夹杂物数密度可降低至1个/mm2以下,夹杂物面积分数可降至16×10-6以下,最大直径可降至18μm以下。轧板中D类和DS类夹杂物均小于1.0级,达到了高级优质钢的要求。研究结果为洁净钢的稳定生产提供了一定的参考。

In order to control T[O]content and inclusions of Q690 steel,improve cleanliness and seek suitable refi-ning slag system,the control status of refining slag system and inclusions in the original process was investigated firstly.The morphology,size and composition of inclusions larger than 2μm in steel were detected and analyzed by Aspex automatic scanning electron microscope,and the time of calcium treatment was determined.Secondly,the thermodynamic calculation of refining slag-liquid steel-inclusions equilibrium was carried out by FactSage software,and the influence of refining slag composition on the composition of inclusions in steel was analyzed.At the same time,laboratory experiments were carried out.Based on the experimental results and theoretical models,the disso-lution rate cloud diagram of Al_(2)O_(3) in CaO-Al_(2)O_(3)-SiO_(2) slag at 1550℃ and 1600℃ was calculated.Finally,the suitable refining slag system of Q690 steel was determined,and the calcium-aluminum ratio of the original process slag system was reduced.The optimized w(CaO)/w(Al_(2)O_(3))of slag system was controlled between 1.8 and 2.0,and the basicity was controlled between 5.O and 7.0.The industrial test results show that the T[O] mass fraction of Q690 steel after RH can be reduced to less than 7×10^(-6),and the maximum diameter of inclusions is reduced from 40-60μm to 10-20μm.The area fraction,number density and maximum diameter of inclusions detected in the steel are significantly reduced.The number density of inclusions in the slab steel samples can be reduced to less than 1 piece/mm^(2),the area fraction of inclusions can be reduced to less than 16 X10-6,and the maximum diameter can be reduced to less than 18μm.The D-type and DS-type inclusions in the rolled plate are all less than 1.O,which meets the requirements of high-quality steel.The research results provide a certain reference for the stable produc-tion of clean steel.