针对邯钢2 250 mm产线在生产宽度1 700 mm 以上宽幅汽车板时边部常出现白斑缺陷而导致产品降级的问题,对缺陷产生原因进行了分析.采用扫描电镜对缺陷微观形貌进行观察,发现明显的蜂窝状"海绵铁组织",能谱分析结果显示有氧化铁存在,因此可以确定热轧生产过程中的边部氧化铁皮破碎压入残留,是缺陷形成的原因之一.另外,钢卷边部氧化铁皮厚度也是影响其酸洗效果的主要因素,并且边浪的存在同样影响酸轧拉矫破鳞及酸洗效果,残留的氧化铁皮在连退后形成白斑缺陷.因此采取了相应的工艺改进措施,包括精轧出口导台两侧增加挡水帘,边部喷嘴封堵,以减少工作辊冷却水边部返水;减小带钢凸度、增加卷取张力、加快钢卷降温,以减小边部氧化铁皮厚度;优化热轧精轧工作辊热凸度和磨损模型计算、弯辊力控制时序、增大酸轧拉矫伸长率,以改善板形,提高酸轧拉矫破鳞效果;优化计划编排,杜绝逆宽轧制,以避免工作辊局部磨损严重对带钢的影响.采取以上措施后,缺陷发生率降低到了 1％以下,大大提高了宽幅汽车板产品的表面质量.
Cause analysis and improvement measures of edge defects of wide width automotive sheets
The causes of white spot defects that often occur at the edges of automotive sheets with a width of over 1 700 mm on the 2 250 mm production line at Hansteel Co.were analyzed which leading to product degradation.By using scanning electron mi-croscopy to observe the microstructure of defects,it was found that there was a clear honeycomb like"sponge iron structure".energy spectrum analysis showed the presence of iron oxide,indicating that the residual edge oxide scale crushed and pressed in strip during hot rolling production was one of the reasons for the formation of defects.In addition,the thickness of the oxide scale on the edge of strip is also the main factor affecting its pickling effect,and the presence of edge waves also affects the straightening and pickling effect of cold rolling.The residual oxide scale forms white spot defects after annealing.Therefore,corresponding process improvement measures have been taken,including adding water curtains on both sides of the finishing mill outlet guide and sealing the edge nozzles to reduce cooling water splashing back at the edge of the work roll.Reduce the convexi-ty of the strip,increase the coiling tension,accelerate the cooling of the coil,and reduce the thickness of the edge oxide scale.Optimize the calculation of thermal convexity and wear model of work roll of finishing rolling mills,control the timing of bending roll force,and increase the elongation of cold rolling straightening to improve strip shape and enhance the effect of straightening on scale breaking.Optimize the plan arrangement and eliminate reverse width rolling to avoid the serious impact of local wear of the work roll on the strip.After taking the above measures,the defect incidence rate was reduced to below 1％,greatly impro-ving the surface quality of wide width automotive sheets.
wide width automotive sheetswhite spot defects of the strip edgeoxide scalethickness of oxide scaleflatness
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