降低ML08Al钢中氮含量及夹杂物的工艺实践

Technical Practices for Reduction in Nitrogen Content and Inclusions in ML08Al Steel

为了解决ML08Al冷镦钢连铸过程中水口絮流、铸坯中氮含量和钙铝酸盐类夹杂物超标等难题,详细分析了转炉—LF精炼—连铸工艺流程存在的问题,提出了优化的工艺方案。结果表明:转炉终点碳质量分数从0.03%~0.04%提高至0.05%~0.06%,出钢铝锭加入量从0.96 kg/t钢减小至0.32 kg/t钢,钢水终点氮质量分数从0.00296%降至0.00183%;LF精炼过程中送电次数从4次减少到2次,软吹时间增加7 min,出站钢水S质量分数从0.007%降至0.003%,氮质量分数从0.00448%降至0.00264%;浇铸过程易发生卷渣。因此,采用新工艺浇铸时钢包采用氩气密封,中间包采用整体套管,并对挡墙设置进行优化,中间包液面波动明显改善,钢水平均氮质量分数从0.00651%降至0.00332%,连浇炉数达到了34炉,基本消除了水口絮流现象。

In order to solve the knotty problems,such as the nozzle clogging,the excess nitrogen content and Ds-type inclusions in billet during the continuous casting of ML08Al cold heading steel,the problems present in process flow including converter-LF refining-continuous casting were analyzed in detail,and an optimized process plan was proposed.The results showed that(a)the mass fraction of carbon at the end-point of the converter increased from 0.03%-to-0.04%to 0.05%-to-0.06%,the amount of aluminum ingots added during converter tapping decreased from 0.96 kg to 0.32 kg per ton of steel,and the end-point nitrogen mass fraction of molten steel decreased from 0.00296%to 0.00183%;(b)as the times of power transmission reduced from 4 to 2,and the soft blowing time increased by 7 min during the LF refining,the mass fraction of sulfur decreased from 0.007%to 0.003%,and the mass fraction of nitrogen decreased from 0.00448%to 0.00264%in the molten steel after refining;and(c)the slag entrainment was prone to occur during the casting process.Therefore,the ladle was sealed with argon gas,the tundish was equipped with an integral sleeve,and the baffle design was optimized during the continuous casting by a new process,and,as a result,the fluctuation of liquid level in tundish was improved obviously,the average mass fraction of nitrogen in molten steel reduced from 0.00651%to 0.00332%,the continuous cast heats reached 34,and the phenomenon of flocculating flow in nozzle was basically eliminated.