Influence of silicon on a quality of zinc coatings
All kinds of steel presented in the DIN 17100, PN-88/H-84020 and PN-86/H-84018 Standards can be hot galvanized. The quality of zinc coatings (luster, smoothness, thickness and adherence) differs for particular kinds and depends on the chemical composition, especially on: carbon (C), phosphorus (P) and silicon (Si) percentage. The content of carbon and silicon may not together exceed 5 %. In case of using the steel with a silicon content out of a permissible levels, a reaction: iron - zinc can run very fast and content of the iron-zinc alloy in the coating will be higher than normally is. In an extreme case, the coating can consists of such the alloy in 100 %. Such effect (the Sandelin's effect) is observed while the silicon content comprises in an interval between 0,03 % and 0,12 % as well as while exceeds 0,3 % (see diagram). Such coating will be mat-grey, rough, non-uniform, very brittle and, as a result, sensitive to deformations and mechanical damages. The adherence of thick coating is reduced in a/m conditions. For these reasons, hot galvanizing of steels with silicon contents described above isn't recommended. The best results are presented for steels with silicon content below 0,03 % or comprising in an interval between 0,15 % and 0,25 %. A temperature of the hot galvanizing process amounts between 450oC and 460oC. It's scientifically proved that technological properties of the steel don't deteriorate during the hot galvanizing process.
