热轧窄带钢冷弯合格率提升实践

PRACTICE OF IMPROVING THE PASS RATE OF COLD BENDING OF HOT ROLLED NARROW STRIP

通过生产统计、化学分析、金相检验及能谱分析,找出了津西160~320 mm窄带钢冷弯开裂的主要原因。结果表明,开裂试样的化学成分及组织与正常带钢无明显差别,但存在3级及以上的硅酸盐夹杂物,其数量多、级别高,且粗系夹杂物中氧化镁和氧化锰含量较高。从硅酸盐夹杂物的生成机理及相关冶金工艺入手,分析了中包容量和中包钢水平均停留时间对夹杂物级别的影响,进而通过优化转炉脱氧合金化,保证钢中Mn/Si≥2.5,中包满液面浇注,稳定浇注周期等工艺措施,使得热轧带钢硅酸盐夹杂物数量及级别都显著降低,冷弯合格率由50%~80%提升至95%以上,大大改善了产品质量。

Through production statistics,chemical analysis,metallographic examination and energy spectrum analysis,the main causes of cold bending cracking of 160~320 mm narrow strip steel in Jinxi are found out.The results show that the chemical composition and structure of the cracked sample are not significantly different from that of the normal strip steel,but there are three level or more silicate inclusions,with a large number and high grade;and the content of magnesium oxide and manganese oxide in the coarse inclusions is high.Based on the formation mechanism of silicate inclusions and related metallurgical processes,the influence of the capacity and the average residence time of liquid steel of tundish on the inclusion is analyzed.Through the measures of optimizing the deoxidization and alloying of converter,ensuring the Mn/Si≥2.5,full level pouring of tundish and stable pouring period,etc.,the quantity and grade of silicate inclusions in hot rolled strip decreased significantly,and the qualified rate of cold bending increased from 50%~80%to over 95%,which greatly improved the product quality.