590 MPa级低合金高强度热镀锌钢板表面亮点缺陷分析

采用SEM、EDS分析了590 MPa级低合金高强度热镀锌钢板表面亮点缺陷的形貌及成分。结果表明,低合金高强钢中合金元素选择性氧化析出的颗粒物尺寸较小时,可以被Zn液中Al完全还原。对比正常位置,析出物颗粒位置没有形成完整致密的Fe₂Al₅Zn_x抑制层,在后续热镀锌过程中,该位置Zn-Fe反应扩散快,镀层生长厚。光整时,该位置形成的压缩片状结构相互连结,宏观表征为表面亮点缺陷。通过降低炉内露点可以抑制低合金高强钢表面合金元素外氧化,进而防止镀层表面亮点缺陷产生。

Analysis of bright spot defect on surface of 590 MPa low-alloy high-strength galvannealed steel sheet

Morphology and element content of bright spot defect on the surface of 590 MPa galvannealed high-strength steel sheet were investigated by SEM and EDS. The results show that the surface oxides produced by the selective oxidation of alloying elements can be reduced completely by the dissolved Al in the Zn bath when the oxides are small enough in the high-strength low-alloy steel. Compared with the normal position, a complete and dense Fe₂Al₅Zn_x inhibitory layer is not formed at the position of the precipitate particles. In the subsequent hot-dip galvanizing process, the Zn-Fe reaction and diffusion at this position are fast, and the coating grows thicker. During skin pass rolling, the compressed sheet-like structures formed at this position are connected with each other, and their macroscopic feature is the surface bright spot defect. By reducing the dew point in the furnace, the external oxidation of alloy elements on the surface of low-alloy high-strength steel can be inhibited, thereby preventing the occurrence of bright spot defects on the surface of the coating.