Hot dipped galvanised hot rolled coil with improved corrosion resistance and good cold forming quality

摘要

The continuous hot dip galvanising of hot strip is today commonplace, in particular for the manufacture of sections. In contrast to the individual piece galvanised strip, continuously galvanised strip possesses the disadvantage of a thinner coating layer thickness and is thus, to date, unsuitable for certain applications. In the construction industry and the street building industry, a layer thickness exceeding 50 #mu#m is sometimes required. The cold formability of galvanised strip is also limited to a coating layer thickness of 30 #mu#m. It therefore became necessary to develop a process which combined the advantages of modern and economic strip galvanising with the greater layer thickness possible in piece galvanising. Good cold formability also had to be guaranteed. The process introduced here fulfils these requirements. Following induction heating, pretreated hot strip is passed continuously through two zinc baths each with a different make up. The double layer up to 70 #mu#m thus formed, shows good formability. Comparisons in corrosion protection prove that the duration of the protection given is markedly higher than that of other metallic coatings. These results open the way to new areas of application for hot dip strip galvanised products.