Patent ID: 8409667
Filing Date: 2013-04-02
Classification: C23C

Abstract:
1. A method for preparing a strip of high-strength steel for galvanisation comprising the steps: heating a strip of steel to an annealing temperature and holding the strip at said annealing temperature, under an oxidising atmosphere of a mixture of a) air or oxygen, and b) a non-oxidizing or inert gas to form an oxide film on the surface of the strip, oxide film comprising iron oxide, said heating of the strip being achieved either by direct flame or by radiation; and cooling the annealed strip and reducing the iron oxide present in the oxide film of the annealed strip under a reducing atmosphere of a mixture of a) hydrogen and b) a second inert gas; wherein the oxidising atmosphere is at least partially separated from the reducing atmosphere, wherein a controlled oxygen level is maintained between 50 and 1,000 ppm during the heating and holding step, and wherein a controlled hydrogen level is maintained in the cooling and reducing step at a value lower than 0.5% volume in the second inert gas.