EFFECT OF ATMOSPHERE IN CONTINUOUS ANNEALING ON ADHESION OF VAPOR ZINC COATED STEEL SHEETS

As an alternative to the Non Oxidizing Furnace (NOF) method, the subject of a continuous heating process for annealing and surface activation of steel sheets prior to vapor zinc coating was taken up. Studies on a laboratory-scale were made up to find out whether production of vapor zinc coated steel sheets with excellent adhesion was possible in a N2 atmospheric gas with limited amount of H2 content using the conventional continuous annealing furnace. As the result, it was found that production of vapor zinc coated steel sheets with superior performance was possible even by the continuous annealing conditions of [700-degrees-C x 45 s annealing --> 400-degrees-C x 240 s overaging] at base steel temperature just before vapor zinc coating of 150-degrees-C and above, if O2 concentration was less than 2.5 x 10(-3) vol% in the 2 vol%H2-H2 gas with dew point of -20-degrees-C.