Thyssenkrupp Steel Ag

Thyssenkrupp Steel Europe Ag

Ronny Leuschner

Manfred Meurer

Wilhelm Warnecke

Sabine Zeizinger

Norbert Schaffrath

Gernot Nothacker

Michael Ullmann

Michael Steinhorst

Harald Hofmann

A process for melt dip coating a strip of high-tensile steel with alloy constituents including zinc and/or aluminum includes the following steps. The strip is heated in a continuous furnace initially in a reductive atmosphere to a temperature of approximately 650&#xb0; C., at which the alloy constituents diffuse to the surface in small amounts. The surface, consisting predominantly of pure iron, is converted into an iron oxide layer by a short heat treatment at a temperature of up to 750&#xb0; C. in a reaction chamber which is integrated in a continuous furnace and has an oxidizing atmosphere. In a subsequent annealing treatment at a higher temperature in a reductive atmosphere, this iron oxide layer prevents the alloy constituents from diffusing to the surface. In the reductive atmosphere, the iron oxide layer is converted into a pure iron layer to which the zinc and/or aluminum are applied in the molten bath with optimum adhesion.

Process for melt dip coating a strip of high-tensile steel

A method for coating a flat steel product manufactured from a high strength steel with a metallic coating, wherein the flat steel product is initially subjected to a heat treatment, in order then, in the heated state, to be hot-dip galvanized with the metallic coating in a melting bath containing overall at least 85% zinc and/or aluminum. The heat treatment includes heating the steel product in a reducing atmosphere, followed by converting a surface of the flat product to an iron oxide layer by a heat treatment lasting 1 to 10 secs in an oxidizing atmosphere, followed by annealing in a reducing atmosphere over a period of time which is longer than the duration of the formation of the iron oxide layer such that the iron oxide layer is reduced at least on its surface to pure iron, followed by cooling the product to a melting bath temperature.

Method for melt immersion coating of a flat steel product made of high strength steel

A method for coating a hot-rolled or cold-rolled steel flat product, containing 6-30% wt. Mn, with a metallic protective layer by hot-clip coating in a melt bath. The coating, achieved with increased production reliability, is optimised by the steel flat product being subjected to a pickling treatment in which the manganese oxide adhering to the steel flat product is essentially fully removed in the pickling bath before the steel flat product enters the melt bath.

Method for coating a hot-rolled or cold-rolled steel flat product containing 6-30 wt% Mn

A method for coating hot-rolled or cold-rolled steel strip containing 6-30 wt %. Mn with a metallic protective layer, includes annealing the steel strip at a temperature of 800-1100&#xb0; C. under an annealing atmosphere containing nitrogen, water and hydrogen and then subjecting the steel strip to hot dip coating. The method provide an economical way of hot dip coating a high manganiferous sheet steel in that, in order to produce a metallic protective layer substantially free from oxidic sub-layers on the steel strip, the % HO/% Hratio of the water content % HO to the hydrogen content % Hin the annealing atmosphere is adjusted as a function of the respective annealing temperature TG as follows: % HO/% H&#x2266;8&#xb7;10&#xb7;T.

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Dortmund, Germany

Ronny Leuschner