双相钢热镀锌表面漏镀缺陷分析及对策

Analysis and countermeasure of skip plating defect on surface of galvanized dual-phase steel

双相钢合金元素的含量较高,在热轧过程中表面氧化铁皮较为严重,导致镀锌过程中还原炉内部合金元素在带钢表面氧化富集,从而影响基板表面的浸润性,造成带钢表面漏镀缺陷。通过扫描电镜、能谱仪对DP590高强钢镀锌生产过程中产生的2种典型漏镀缺陷──不规则状缺陷和圆状缺陷进行了分析,发现基板表面合金元素氧化富集是造成漏镀缺陷的原因。通过采用较大的轧制速度和冷却速度,以及较低的终轧温度(840°C)和卷曲温度(640°C),有效控制了氧化铁皮的生成,改善了酸洗效果;通过提高退火炉的密封性,增加保护气体压力和还原性气体(氢气)含量,降低了炉内的氧含量及露点温度,解决了双相钢的漏镀问题。

Due to high content of alloy elements in dual- phase steel, heavy scale was formed during hot rolling process, leading to the optional oxidation and enrichment of alloy elements inside reducing furnace during galvanizing process, affecting the wettability of substrate surface and resulting in skip plating defect on galvanized steel sheet surface. In the paper, two typical skip plating defects i.e. irregular- and round-shaped defects formed in the production of galvanized DP590 high-strength steel sheet were analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The oxidation and enrichment of alloy elements on steel surface are the main reasons for skip plating defect. The heavy scale can be effectively controlled and the pickling effect improved by hot rolling and cooling at higher speeds as well as finishing rolling and cooling at lower temperatures （840 ℃ and 640 ℃, respectively）. The content of oxygen in reducing furnace and the dew point temperature are decreased, and the problem of skip plating on dual-phase steel surface is solved by improving the tightness of annealing furnace as well as increasing the pressure of protective gas and the content of reducing gas （i.e. H2）.