合金化热镀锌板表面条状缺陷原因分析

针对合金化热镀锌板表面常见的“边部不规则长条状”缺陷和“柳叶状”缺陷,利用扫描电镜对其形貌进行了分析。“边部不规则长条状”缺陷分布于带钢上下表面两边部,为不规则细长条,严重时可见缺陷整卷全长连续分布;“柳叶状”缺陷宏观形貌不规则,一端细尖一端较宽,形似“柳叶”。缺陷部位完全溶锌后观察到基板存在翘皮和还原铁,轻微抛光基板表面后发现未被完全还原的氧化铁皮,缺陷部位截面可见翘皮处同样存在氧化铁皮,未见炼钢保护渣、氧化铝夹杂、二次氧化颗粒等,可以确定两种缺陷均来自于热轧阶段。“边部不规则长条状”缺陷为热卷边部翘皮,即边线缺陷遗传导致,通过针对性调控炉内加热工艺、粗轧及除鳞等工艺,该类缺陷得到控制;“柳叶状”缺陷来源于由热轧通道线辊面粘铁导致中间坯表面损伤,虽经精轧轧合,但皮下存在氧化铁,冷轧后以及镀锌合金化时暴露出缺陷,通过定期检查热轧辊道、优化设备控制程序逻辑大幅降低了该类缺陷的发生率。

Causes analysis of strip defects on the surface of galvannealed sheets

Aiming at the common “irregular strip-shaped on the edge” defects and “willow-shaped” defects on the surface of galvannealed sheet, the morphologies were analyzed by scanning electron microscope. “Irregular strip-shaped on the edge” defects are distributed on both sides of the upper and lower surfaces of the strip, which are irregular and elongated strips. In severe cases, the defects can be seen to be continuously distributed throughout the entire length of the coil. The macroscopic appearance of “willow-shaped” defects is irregular, one end is thin and the other is wider, and it resembles a “willow leaf”. After the zinc was completely dissolved in the defect site, it was observed that scar defect and reduced iron existed on the substrate. After slightly polishing the surface of the substrate, oxide scale that was not completely reduced was found. Oxide scale was also found in the scar defect on the cross section of the defect site, and no steel-making mold slag, aluminum inclusions and secondary oxidation particles were found. Both defects come from the hot rolling stage. The “irregular strip-shaped on the edge” defects are caused by the edge scar defect, that is, the inheritance of the edge defect. Through targeted regulation of the furnace heating process, roughing rolling and descaling processes, such defects can be controlled. The “willow-shaped” defects originate from the surface damage of the intermediate billet caused by the oxide scale sticking on the surface of the table rolls. After the damage is finished rolling, there is iron oxide under the skin, and the defects are exposed after cold rolling and during galvannealing. Regular inspection of the hot rolling table and optimization of the equipment control program logic have greatly reduced the incidence of such defects.