Coated Steel Sheet or Strip

Abstract

The invention relates to a coated steel sheet or strip with a ground coating made of steel, onto at least one upper side of which a coating is applied by hot-dip galvanizing, the coating being formed from a melt consisting of 0.05-0.30% by weight Al and 0.2-2.0% by weight Mg, the remainder being zinc and unavoidable impurities, and, with a coating thickness of a maximum of 3.5 μm on each side and a coating weight of a maximum 25 g/m 2 on each side, guarantees that the steel sheet, in the salt spray mist test carried out in accordance with DIN 50021-SS, shows the first formation of red rust at the earliest after 250 hours. With such a sheet or strip, a flat steel product is provided which possesses an optimum combination of high corrosion resistance and optimum weldability and which is particularly well-suited for use as a material for motor vehicle chassis construction or for the construction of domestic appliances.

1 - 5 . (canceled) 
     
     
         6 . A method for the manufacture of a steel sheet or strip coated on at least one of side with a coating of 0.05-0.30% by weight Al and 0.2-2.0% by weight Mg, the remainder being zinc and unavoidable impurities, the coated steel strip, in a salt spray mist test carried out in accordance with DIN 50021-SS, shows the first red rust formation at the earliest after 250 hours, the method comprising:
 annealing an uncoated steel strip;   conducting the annealed uncoated steel strip through a galvanizing bath including 0.05-0.30% by weight Al and 0.2-2.0% by weight Mg, the remainder being zinc and unavoidable impurities, to form the coated steel strip; and   adjusting a coating layer thickness and a coating weight on the coated steel strip emerging from the galvanizing bath using a stripper nozzle;   wherein (i) a surface of the galvanizing bath is kept under an inert gas flow in relation to the surrounding atmosphere, to inhibit formation of slag or inter-metallic phases; and (ii) the coating layer thickness is up to 3.5 μm on each side and the coating weight is up to 25 g/m 2  on each side.   
     
     
         7 . The method of  claim 6  wherein the coating includes 0.4-1.0% by weight Mg. 
     
     
         8 . The method of  claim 7  wherein the coating includes more than 0.5% by weight Mg. 
     
     
         9 . The method of  claim 6  wherein the Al content of the galvanizing bath amounts to 0.12-0.14% by weight. 
     
     
         10 . The method of  claim 7  wherein the Al content of the galvanizing bath amounts to 0.12-0.14% by weight. 
     
     
         11 . The method of  claim 8  wherein the Al content of the galvanizing bath amounts to 0.12-0.14% by weight. 
     
     
         12 . The method of  claim 6  wherein the Al content of the galvanizing bath amounts to at least 0.15% by weight. 
     
     
         13 . The method of  claim 7  wherein the Al content of the galvanizing bath amounts to at least 0.15% by weight. 
     
     
         14 . The method of  claim 8  wherein the Al content of the galvanizing bath amounts to at least 0.15% by weight.