Why does the hot dip galvanization generally use the boiling steel as galvanizing original plate?
Because: if the steel base contains higher Si, it will bring the following difficulties to hot galvanizing:
(1) the steel base contains a relatively high degree of sedation steel, and its zinc coat (Fezn) is thicker.
(2) sedation steel with higher Si is included in the steel base, and its coating is in gray state, while its adhesion decreases
(3) as the calcined steel contains other elements, such as excessive c. Si,Mn,P, etc., some of these elements prevent the preferential formation of Fe2Als, while some of them aggravate the diffusion of Zn to the Fe2Als intermediate phase layer, resulting in defects such as plating shedding and cracks.
Conclusion: for a long time, the galvanized steel with Si content less than 0.07% is often used as the original plate.
(1) all measures should be taken to prevent excessive oxidation of silicon.Because the influence of silicon on hot galvanizing in steel-base depends mainly on Si0, rather than on free silicon, Si02 is exactly the main reason for the formation of 5 phase (FeZns), leading to poor adhesion and making the galvanizing gray.
(2) all possible measures should be taken to clean up the generated Si02.Clear method of Si02: because Si0 is acidic oxide and is not easily dissolved in dilute acid, strong pickling or strong Et method should be adopted to remove Si0.