超低碳钢冷轧卷“头部黑线”缺陷分析与控制

ANALYSIS AND CONTROL OF HEAD BLACK LINE DEFECT OF COLD ROLLED ULTRA-LOW CARBON STEEL COIL

针对超低碳冷轧连退卷带头20~30 m内频繁出现黑线缺陷,导致了批量不合格品产生而影响订单交期的问题,采用金相显微镜、扫描电子显微镜等检测分析手段对缺陷进行了分析,并进行了铸坯端面预制缺陷轧制中间坯的工业试验验证,锁定了缺陷产生的原因。结果表明,“头部黑线”缺陷与保护渣卷渣类、氧化铝夹杂类和气泡类缺陷形貌区别明显,与基体无连接,呈分开状态,主要由Fe、Al元素组成,判断此缺陷为外来异物。通过全流程追溯,发现热轧成材率攻关后,超低碳钢中间坯切头量有所减少,无法将喷号焊丝全部切除,铸坯打号机的喷号焊丝压入导致该类“黑线缺陷”的产生。基于此,将超低碳钢热轧中间坯切割量控制在300mm,喷号机的压空压力使用标准调整为4 bar,冷轧卷头部黑线缺陷问题得到了有效改善,超低碳钢表面质量合格率提高了4.03%。

In response to the frequent occurrence of black line defects within 20~30 m of the head of the ultra-low carbon cold rolling continuous unwinding coil,resulting in a batch of non-conforming products,quality losses,and affecting the delivery time of the order.The defects were analyzed by means of metallographic microscope and scanning electron microscope,and the industrial test was carried out to verify the rolling of intermediate billets with prefabricated defects on the end face of the casting billet,and the cause of the defects was locked.The results show that the appearance of the"black line on the head"defect is obviously different from that of the protective powder,alumina inclusions and bubbles,and it is not connected with the matrix,and is in a separate state,mainly composed of Fe and Al elements,which indicates that the defect is a foreign object.Through the whole process tracing,it is found that after the yield of hot rolling,the cutting head of the ultra-low carbon steel intermediate blank is reduced,and the spraying welding wire cannot be completely removed,and the spraying welding wire of the casting blank marking machine is pressed into the production of this kind of"black line defect".Based on this,the cutting amount of the middle billet of the ultra-low carbon steel hot rolling is controlled at 300 mm,the air pressure of the spraying machine is adjusted to 4 bar,the black line defect of the cold rolling coil head is effectively improved,and the pass rate of the ultra-low carbon steel surface quality is increased by 4.03%.