METHOD FOR THE PREOXIDATION OF STRIP STEEL IN A REACTION CHAMBER ARRANGED IN A FURNACE CHAMBER

Abstract

Method for the preoxidation of high-strength strip steel. The invention relates to an improved method for the preoxidation of high-strength strip steel in a reaction chamber arranged in a furnace chamber. The reaction chamber is sealed at a strip entrance and a strip exit against gas exchange between the furnace chamber and the reaction chamber, and a gas that forms an oxidizing atmosphere in the reaction chamber is introduced, and the gas is continuously circulated within the reaction chamber

Claims

1. A method for preoxidation of oxidation-sensitive steel strip in a reaction chamber arranged in a furnace chamber, characterized in that the reaction chamber is sealed at a strip entrance and a strip exit against gas exchange between the furnace chamber and the reaction chamber and a gas which forms an oxidizing atmosphere in the reaction chamber, is introduced and is continuously circulated inside the reaction chamber in a closed circuit, wherein the composition of the gas is regulated and losses due to leakages and consumption are compensated.

2. The method for preoxidation according to claim 1, characterized in that the oxidizing gas is evacuated from the reaction chamber, cooled, fed to a fan, enriched with air and fed back into the reaction chamber in order to achieve a good homogeneity of the atmosphere.

3. The method for preoxidation according to claim 2, characterized in that the gas is supplied to the strip surface with high kinetic energy density in a controlled and uniform manner via at least one nozzle system with the aid of nitrogen as carrier gas in order to avoid laminar boundary layer effects on the strip surface.

4. The method for preoxidation according to claim 3, characterized in that the oxygen content of the atmosphere in the reaction chamber is kept at a minimum of 1.5 to a maximum of 5 vol %, in order to thereby achieve a sufficient buffer against hydrogen ingress from the furnace chamber into the reaction chamber.

5. The method for preoxidation according to claim 1, characterized in that a vent is assigned to the reaction chamber to compensate for changes in volume.

6. The method for preoxidation according to claim 5, characterized in that the vent is preferably controlled so that the internal pressure of the reaction chamber corresponds to the pressure of the surrounding furnace atmosphere to minimize gas exchange due to inevitable leaks.

7. The method according to claim 1, characterized in that the oxidation-sensitive steel contains at least one member selected from the following alloy components: Mn>0.5%, Al>0.2%, Si>0.1%, Cr>0.3%.

Description

[0010] According to the teaching of the invention, this object is achieved by the features set forth in claim 1, in particular in that the reaction chamber is sealed at a strip entrance and a strip exit against gas exchange between the furnace space and the reaction chamber and a gas, which forms an oxidizing atmosphere in the reaction chamber, is introduced and is continuously circulated inside the reaction chamber in a closed circuit, with the composition of the gas being regulated and losses due to leakage and consumption are compensated.

[0011] In this way, it is possible to produce a particularly uniform oxide layer on the strip surface, so that defects in the subsequent hot-dip coating are avoided and the quality of the end product is improved and scrap is reduced.

[0012] The reaction chamber is sealed off from the furnace space and in particular at the strip entrance and strip exit against gas exchange.

[0013] The atmosphere is constantly circulated. For this purpose, the gas is evacuated from the reaction chamber, cooled, fed to a fan, enriched with fresh air and fed back into the chamber. This ensures good homogeneity of the atmosphere.

[0014] A further desired effect is that gas with high kinetic energy density is supplied to the strip surface in a controlled and uniform manner via nozzle systems (at least one nozzle system) with the aid of nitrogen as carrier gas. This is necessary to avoid laminar boundary layer effects.

[0015] In order to achieve a sufficient buffer against the ingress of hydrogen, the oxygen content of the atmosphere in the reaction chamber is at least 1.5 vol % to a at most 5 vol %.

[0016] The reaction chamber has a vent to compensate for changes in volume. This vent is preferably regulated in such a way that the internal pressure of the reaction chamber corresponds to the pressure of the surrounding furnace atmosphere and the gas exchange via the inevitable leaks is minimal.

[0017] These measures result in a well controllable oxidation process and prevent impairment of the furnace atmosphere surrounding the reaction chamber.

[0018] The oxidation-sensitive steel can contain at least one member selected from the following alloy components: Mn>0.5%, Al>0.7%, Si>0.1%, Cr>0.3%.