热镀锌BH180钢板表面漏镀缺陷测试与分析

Test and analysis of plating leakage defects on surface of hot galvanized BH180 sheet

对国内某钢厂热镀锌机组生产烘烤硬化钢产品BH180出现的表面漏镀问题进行了分析与研究,通过观察缺陷的宏观与微观形貌,检测缺陷处的成分,分析漏镀的形成机理。发现缺陷处冷轧基板表面存在大量凹坑且呈橘皮状,经过清洗工艺处理后,凹坑处仍存在油脂混合物残留,经过退火工艺处理后有机物残留碳化并沉积在凹坑处,降低了锌液的浸润性,抑制了基板表面Fe_(2)Al_(5)抑制层的形成,最终导致漏镀缺陷产生。对比漏镀缺陷卷基板成分和正常卷基板成分发现,缺陷基板的硼含量超标,微量硼元素在晶界偏聚导致基板存在粗大块状和长条状晶粒+细小晶粒的混合组织,存在混合晶粒组织的热轧基板经酸洗冷轧后表面会形成橘皮状凹坑。钢厂对BH180基板的硼元素成分含量严加控制,并提高镀锌清洗段工艺效率后,该产品表面漏镀问题得到有效解决。

The issue of surface plating leakage on bake-hardened steel BH180 products produced by a hot-dip galvanizing production line in a domestic steel plant was analyzed and studied.The formation mechanism of plating leakage was analyzed by observing the macroscopic and microscopic morphology of defects as well as detecting the composition of defects.It was found that there were numerous pits on the surface of substrate where the defects appeared as orange peel shapes.Even after cleaning,the grease mixture residue remained in these pits.The organic residues were carbonized and deposited within the pits during annealing,which reduced the wettability of zinc solution and inhibited the formation of Fe_(2)Al_(5) inhibition layer on the substrate surface.As a result,the plating leakage defects were generated.By comparing the composition of the defective coil substrate with that of the normal coil substrate,it was found that the boron content in the defective substrate exceeded the standard.The trace boron elements were segregated at the grain boundaries,which led to the existence of mixed structure of coarse block and long grain and fine grain in the substrate.The hot-rolled substrate with mixed grain structure would form orange peel pits after pickling and cold rolling.After strictly controlling the boron content in BH180 substrate and improving the process efficiency of galvanized cleaning section,the problem of plating leakage of BH180 could be effectively solved.