输电铁塔热浸镀锌钢板单面锌瘤成因分析

Cause analysis on pimples distributed on one side of hot-dip zinc-coated steel sheet for transmission tower

针对输电铁塔Q235钢板热浸镀锌层单面出现的锌瘤缺陷,利用研究级正置显微镜(UMM)、扫描电镜(SEM)和能谱仪(EDS)分析了锌瘤的微观结构。结果表明,锌瘤热浸镀锌层的η相内存在大量块状ζ相粒子,ζ相出现粗大柱状形态的爆发式增长。锌瘤侧的Q235钢表面存在直径为50~100μm且与锌瘤位置对应的凹坑。调查生产现场后发现,这些凹坑为氧化锈蚀坑,它们可以扩大Zn/Fe反应界面面积,增强Zn/Fe反应活性,并为ζ相的爆发式增长提供充足的Fe原子,进而导致锌瘤产生。建议实施严格的来料管理,改善钢板的储存条件,以及加强过程管控,防止严重锈蚀的钢板进入热浸镀锌生产线。

The microstructure of pimples distributed on one side of hot-dip zinc-coated Q235 steel sheet for transmission tower was analyzed by using scientific grade upright metallurgical microscope(UMM), scanning electron microscope(SEM),and energy-dispersive spectrometer(EDS). The results showed that there were plenty of blocky ζ phase particles inside the η phase of zinc coating at the position of pimple, and the ζ phase grew explosively and transferred to large column. Some pits with a diameter of 50-100 μm were distributed at the same positions of pimples on the surface of Q235 steel substrate. It was found that the pits resulted from the oxidative corrosion of substrate by production site investigation. The pits not only increase the reaction interface area and reactivity between Zn and Fe, but also offer sufficient Fe atoms for the explosive growth of ζ phase, leading to the formation of pimple. It is necessary to prevent the use of steel sheets with serious pitting by taking some measures such as raw material inspection, improvement on storage conditions, and strict process control.