Flat Steel Product and Method for Producing a Flat Steel Product

Abstract

A flat steel product, intended to be formed into a component by hot press forming and having a base made of steel, onto which a metal anti-corrosion coating of a Zn or a Zn alloy is applied. A separate finishing coat is applied to at least one of the free surfaces of the flat steel product. The finishing coat includes at least one base metal compound (oxide, nitride, sulphide, sulphate, carbide, carbonate, fluoride, hydrate, hydroxide, or phosphate). Also, a method enabling the production of a flat steel product of this kind.

1 . A flat steel product intended for heat treatment, comprising a separate finishing coat is-applied to at least one of the free surfaces of the flat steel product, said finishing coat comprising at least one oxide-, nitride-, sulphide-, sulphate-, carbide-, carbonate-, fluoride-, hydrate-, hydroxide- or phosphate-compound of a base metal. 
     
     
         2 . The flat steel product according to  claim 1 , Wherein the surface density of the finishing coat is between 0.01 and 15 g/m 2 . 
     
     
         3 . The flat steel product according to  claim 1 , wherein the finishing coat thickness is between 0.01 and 5 μm. 
     
     
         4 . The flat steel product according to  claim 1 , further comprising a steel base layer and a metal protective coating for corrosion protection applied to the base layer, wherein the finishing coat is applied to the protective coating. 
     
     
         5 . The flat steel product according to  claim 1 , wherein the metal of the compound contained in the finishing coat belongs to the group of alkaline earth metals. 
     
     
         6 . The flat steel product according to  claim 1 , wherein the metal of the compound belongs to the group of alkaline metals. 
     
     
         7 . The flat steel product according to  claim 1 , wherein the metal of the compound belongs to the group of semi-metals. 
     
     
         8 . The flat steel product according to  claim 1 , wherein the metal belongs to the group of transition metals. 
     
     
         9 . The flat steel product according to  claim 1 , wherein the metal of the compound belongs to the group consisting of Na, K, Mg, Ca, B, Al, Si, Sn, Ti, Cr, Mn, and Zn. 
     
     
         10 . The flat steel product according to  claim 1 , wherein the compound present in the finishing coat is particulate. 
     
     
         11 . The flat steel product according to  claim 10 , wherein the average diameter of the particles in the compound is between 0.01 and 5 μm. 
     
     
         12 . The flat steel product according to  claim 1 , wherein the finishing coat further comprises up to 15% wt. of carbon black or graphite. 
     
     
         13 . A method for producing a flat steel product, comprising the following steps:
 a) provision of a flat steel product,   b) application of a finishing coat to the flat steel product by
 b.1) applying a coating liquid to the flat steel product, wherein the coating liquid comprises between (in % wt.) 5 and 50% of an oxide, nitride-, sulphate-, sulphide-, carbide-, carbonate-, fluoride-, hydrate-, hydroxide- or phosphate-compound of a base metal, between 1 and 20% of a binder and the remainder water, and optionally up to 15% wt. of carbon black or graphite, 
 b.2) setting the thickness of the finishing coat to a thickness of between 0.1 and 5 μm and 
   c) drying the finishing coat.   
     
     
         14 . The method according to  claim 13 , wherein the coating liquid contains between 5 and 35% wt. of the base metal compound. 
     
     
         15 . The method according to  claim 13 , wherein the coating liquid contains between 2 and 10% wt. of the binder. 
     
     
         16 . The method according to  claim 13 , wherein the coating liquid contains between 30 and 94% wt. water as a solvent. 
     
     
         17 . The method according to  claim 13 , wherein the method steps are performed in continuous succession without interruption. 
     
     
         18 . The method according to  claim 13 , wherein the flat steel product provided in step a) is a blank cut from a strip or sheet, and the method further comprises heating the flat steel product after drying the finishing coat based on the drying temperature to a deformation temperature required for hot forming and hot forming the heated flat steel product into a component. 
     
     
         19 . The method according to  claim 18 , wherein the formed component is rapidly cooled from the deformation temperature in order to produce a martensitic structure in the component.