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

doi:10.13251/j.issn.0254-6051.2022.06.048

Abstract

Abstract: 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.

Key words: low-alloy high-strength galvannealed steel sheet, bright spot defect, selective oxidation, dew point

CLC Number:

TG174

Zhao Chuanxiang. Analysis of bright spot defect on surface of 590 MPa low-alloy high-strength galvannealed steel sheet[J]. Heat Treatment of Metals, 2022, 47(6): 270-273.

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