Method for producing a sheet steel product protected against corrosion

Abstract

A cost-favorable process for production of corrosion-resistant sheet steel products, having good characteristics of use for certain application purposes includes applying a zinc-containing coating by electro-galvanizing a flat steel product, finally cleaning mechanically and/or chemically the flat steel product, applying a magnesium-based coating to the finally cleaned zinc-containing coating by means of vapour deposition, and heat treating the coated flat steel product to form a diffusion or convention layer between the zinc-containing coating and the magnesium-based coating at a temperature of 320 ° C. to 335 ° C. under normal atmosphere.

1 . A process for manufacturing corrosion-resistant flat steel products, comprising:
 applying a zinc-containing coating by electro-galvanizing a flat steel product,   mechanically and/or chemically finally cleaning the flat steel products,   directly applying to the finally cleaned zinc-containing coating by means of vapor deposition a second coating, the second coating being magnesium based, and   under normal atmosphere heat treating the flat steel product after applying the second coating to form a diffusion or convection layer between the zinc-containing coating and the magnesium-based coating, at a heat treatment temperature of 320° C. to 335° C.   
   
   
       2 . The process according to  claim 1 , wherein the flat steel product provided with the zinc-containing coating, in the course of its final cleaning, is chemically pre-conditioned by rinsing with an alkaline pre-conditioning agent. 
   
   
       3 . The process according to  claim 1  wherein the flat steel product, provided with the zinc-containing coating, in the course of its final cleaning, is pickled by rinsing with an acid. 
   
   
       4 . The process according to  claim 3 , wherein after pickling the flat steel product is rinsed with de-mineralized water. 
   
   
       5 . The process according to  claim 1  wherein heat treating the flat steel product after applying the second coating is carried out within a duration of 15 seconds at most. 
   
   
       6 . The process according to  claim 1 , wherein the flat steel product, provided with the zinc-containing coating has on its free surface a roughness Ra of at least 1.4 μm prior to vapor deposition. 
   
   
       7 . The process according to  claim 1 , wherein a nib rate RPC of the flat steel product, provided with the zinc-containing coating, prior to vapor deposition, is at least 60 per cm. 
   
   
       8 . The process according to  claim 1 , wherein the flat steel product, provided with the zinc-containing coating, before entering the vapor deposition, is heated to a temperature above ambient temperature but below an alloying temperature of the magnesium coating. 
   
   
       9 . A process for manufacturing corrosion-resistant flat steel products, comprising:
 applying a first coating including zinc by electro-galvanizing a flat steel product,   applying a second coating comprising magnesium by vapor deposition to the first coating without fine cleaning the first coating, and   heat treating the flat steel product with first and second coatings under normal atmosphere to form a diffusion or convection layer between the first and second coatings, at a heat treatment temperature of 320° C. to 335° C.   
   
   
       10 . The process according to  claim 9  wherein heat treating the flat steel product after applying the second coating is carried out within a duration of 15 seconds at most. 
   
   
       11 . The process according to  claim 9 , wherein the flat steel product, provided with the first coating has on its free surface a roughness Ra of at least 1.4 μm prior to applying the second coating. 
   
   
       12 . The process according to  claim 9 , wherein a nib rate RPC of the flat steel product including the first coating, but prior to vapor deposition of the second coating, is at least 60 per cm. 
   
   
       13 . The process according to  claim 9 , wherein the flat steel product, provided with the first coating, before application of the second coating, is heated to a temperature above ambient temperature but below an alloying temperature of the second coating.