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In hot-dip galvanizing process, air jet wiping control is so crucial to determine the coating thickness and uniformity of the zinc layer on the steel strip. A numerical simulation of gas-jet wiping in hot-dip galvanizing was conducted to minimize the occurrence of edge over coating (EOC). The causes of EOC were identified by contrasting and analyzing the airflow fields on the strip edge with and without a baffle. The factors influencing the airflow field on the strip edge during the change in the gap between the baffle and the strip edge were also analyzed. The effect of the distance between the air knife and the strip was evaluated. Technological parameters with on-site guidance role were obtained by combining them with the actual production to elucidate the role of the baffle in restraining the occurrence of EOC. The uniform distribution of pressure and coating thickness on the strip is achieved when the distance of the baffle from the strip edge is about 0.3 times of the jetting distance.

The selective oxidation behaviors of a DP780 steel during recrystallization under different annealing atmospheres have been investigated in a hot dip process simulator (HDPS). The surface chemistry and morphology were analyzed by glow discharge optical emission spectroscopy (GDOES) and scanning electron microscopy (SEM) respectively. The results indicate that the dew point and hydrogen content in the annealing atmosphere have great effects on selective oxidation, and the influence of dew point is slightly stronger than that of hydrogen content. Under the higher dew point and lower hydrogen content, resulting from the increased tendency of internal oxidization of Mn and Cr, the amount and size of oxides dispersed on the external surface decrease, which finally improves the wetting between the annealed substrate and the Zn bath.

Grain size and texture are important factors which affects the coating properties of hot-dip galvanized steel. In this study, different skin passing parameters are controlled to achieve the optimal control of grain size distribution and texture of zinc coating. Specimens were prepared from industry CGL and its coating grain size and texture were evaluated using metallography microscope, SEM and EBSD. The results show that uniform and fine grain size can be achieved by controlled skin-passing. Also, twinning of zinc which normally considered harmful for coating during stamping can be dramatically decreased. Furthermore, the EBSD analysis show that by controlled skin-passing, basal texture component ratio increased distinguishingly which is believed beneficial for stamping. Thus, the further potential benefits for curbing stamping defects of hot-dip galvanized steel are also intriguing.