Method for Producing a Sheet Metal Component by Hot-Forming a Flat Steel Product Provided with an Anti-Corrosion Coating

Abstract

A flat steel product is provided, including a steel substrate made of a steel which consists of, in % by weight, 0.07-0.4% C, 1.0-2.5% Mn, 0.06-0.9% Si, ≤0.03% P, ≤0.01% S, ≤0.1% Al, ≤0.15% Ti, ≤0.6% Nb, ≤0.005% B, ≤0.5% Cr, 50.5% Mo, where the sum of Cr and Mo is ≤0.5%, and, as the remainder, Fe and unavoidable impurities, and including an anti-corrosion coating which is formed from, in % by weight, ≤15% Si, ≤5% Fe, ≤5% of at least one alkaline earth or transition metal and, as the remainder, Al and unavoidable impurities. If the anti-corrosion coating contains ≤0.1% by weight of the alkaline earth or transition metal, a solution containing at least one alkaline earth or transition metal is applied to the anti-corrosion coating of the flat steel product. Then, the flat steel product is flexibly cold-rolled to produce the portions of different thicknesses. Then, it is heated to 800-1000° C. in an atmosphere with >15% by volume O 2 until an amount of thermal energy Js of >44,000 kJs and ≤400,000 kJs has been introduced.

1 . A method for producing a sheet metal component by hot-forming a flat steel product which is provided with an anti-corrosion coating, and which, by flexible cold rolling, is provided with at least one portion which has a different thickness than another adjoining portion of the flat steel product, wherein the transition between the portions of the flat steel product of different thicknesses takes place abruptly, the method comprising the following steps:
 a) providing a flat steel product comprising a steel substrate produced from a steel which, in wt %, consists of 0.07-0.4% C, 1.0-2.5% Mn, 0.06-0.9% Si, up to 0.03% P, up to 0.01% S, up to 0.1% Al, up to 0.15% Ti, up to 0.6% Nb, up to 0.005% B, up to 0.5% Cr, up to 0.5% Mo, wherein the sum of the content of Cr and Mo is at most 0.5%, and, as the remainder, consists of iron and unavoidable impurities, and comprising an anti-corrosion coating applied to the steel substrate, which coating is formed from, in wt %, up to 15% Si, up to 5% Fe, optionally up to 5% of at least one alkaline earth metal or transition metal, and, as the remainder, from Al and unavoidable impurities, then   b) in the event that the anti-corrosion coating contains no or less than 0.1 wt % of the at least one alkaline earth metal or transition metal, applying a solution containing at least one alkaline earth metal or transition metal to the anti-corrosion coating of the flat steel product,   c) flexible cold rolling of the flat steel product in order to produce the portions of different thickness on the flat steel product, then   d) heating the flexibly cold-rolled flat steel product to a hot-forming temperature of 800-1000° C. in an atmosphere containing more than 15 vol. % oxygen over a holding period which is sufficient to introduce a thermal energy quantity Js of more than 44,000 kJs and at most 400,000 kJs into the flat steel product, so that, after heating, the surface of the anti-corrosion coating of the flat steel product is densely coated with a layer consisting of a primary oxide of the at least one alkaline earth metal or transition metal contained in the anti-corrosion layer optionally applied in step b), then   e) hot-forming the flat steel product to form the sheet metal component.   
     
     
         2 . The method according to  claim 1 , wherein the thickness of the flat steel product provided in step a) is 0.6-7 mm. 
     
     
         3 . The method according to  claim 2 , wherein the Si content of the anti-corrosion coating of the flat steel product is at least 3 wt. %. 
     
     
         4 . The method according to  claim 3 , wherein the Fe content of the anti-corrosion coating of the flat steel product is at least 1 wt. %. 
     
     
         5 . The method according to  claim 4 , wherein the anti-corrosion coating of the flat steel product has a content of, in total, at least 0.1 wt % alkaline earth metals or transition metals. 
     
     
         6 . The method according to  claim 5 , wherein the anti-corrosion coating of the flat steel product has a content of, in total, at least 0.11 wt % alkaline earth metals or transition metals. 
     
     
         7 . The method according to  claim 6 , wherein the anti-corrosion coating of the flat steel product has a content of, in total, at most 1.5 wt % alkaline earth metals or transition metals. 
     
     
         8 . The method according to  claim 7 , wherein the anti-corrosion coating of the flat steel product has a content of, in total, at most 0.6 wt % alkaline earth metals or transition metals. 
     
     
         9 . The method according to  claim 8 , wherein the anti-corrosion coating of the flat steel product or the solution applied according to step b) comprises magnesium as the at least one alkaline earth metal or transition metal. 
     
     
         10 . The method according to  claim 9 , wherein the coating weight of the anti-corrosion coating of the flat steel product is 30-100 g/m 2  per coated side of the flat steel product. 
     
     
         11 . The method according to  claim 10 , wherein the anti-corrosion coating is applied to the steel substrate of the flat steel product by hot dip galvanizing. 
     
     
         12 . The method according to  claim 11 , wherein the heating of the flat steel product in step c) takes place in a continuous furnace by radiant heat and the holding period is 100-900 s.