Method for producing a steel component by hot forming and steel component produced by hot forming

Abstract

A method for producing a steel component provided with a metallic coating which protects against corrosion, comprising the following steps: coating a steel flat product, produced from a low-alloy heat-treated steel, with an Al coating which contains at least 85% wt. Al and optionally up to 15% wt. Si; coating the steel flat product provided with the Al coating with a Zn coating which contains at least 90% wt. Zn; heating the steel flat product to a hot-forming temperature which is at least 750° C.; hot forming the heated steel component made from the steel flat product; and cooling the hot-formed steel component sufficiently quickly to form a tempered or martensitic structure.

1 - 30 . (canceled) 
     
     
         31 . A method for producing a steel component provided with a metallic coating which protects against corrosion, comprising the following production steps:
 coating a steel flat product, produced from a low-alloy heat-treated steel, with an Al coating which contains at least 85% wt. Al and optionally up to 15% wt. Si;   coating the steel flat product provided with the Al coating with a Zn coating which contains at least 90% wt. Zn;   heating the steel flat product to a hot-forming temperature which is at least 750° C.;   hot forming the heated steel component made from the steel flat product; and   cooling the hot-formed steel component sufficiently quickly to form a tempered or martensitic structure.   
     
     
         32 . The method according to  claim 31 , wherein the hot-forming temperature is 850 to 950° C. 
     
     
         33 . The method according to  claim 31 , wherein the Al coating is applied by hot-dip aluminising. 
     
     
         34 . The method according to  claim 31 , wherein the Al coating contains 5-12% wt. Si. 
     
     
         35 . The method according to  claim 31 , wherein the Zn coating is applied by hot-dip galvanising or deposited in a PVD process onto the Al layer which was previously applied onto the steel flat product. 
     
     
         36 . The method according to  claim 31 , wherein the Zn coating is deposited on the Al coating electrolytically. 
     
     
         37 . The method according to  claim 36 , wherein the Zn coating contains at least 99% wt. Zn. 
     
     
         38 . The method according to  claim 35 , wherein besides Zn at least one element from the group comprising Al, Mg, and Si is contained in the Zn coating. 
     
     
         39 . The method according to  claim 31 , wherein the steel flat product provided with the Al coating is subjected to skin-pass rolling before the Zn coating is applied. 
     
     
         40 . The method according to  claim 31 , wherein the steel flat product provided with the Al coating is subjected to pickling before the Zn coating is applied. 
     
     
         41 . The method according to  claim 31 , wherein the Al coating and subsequently the Zn coating are applied in production steps following continuously one after the other. 
     
     
         42 . The method according to  claim 31 , wherein the Al coating and subsequently the Zn coating are applied in production steps which do not follow continuously one after the other. 
     
     
         43 . The method according to  claim 31 , wherein the steel flat product is formed into the steel component in a single hot-forming step. 
     
     
         44 . The method according to  claim 31 , wherein the forming takes place in multiple stages and at least one forming stage is carried out as a hot-forming step which follows heating to hot-forming temperature. 
     
     
         45 . The method according to  claim 44 , wherein before heating to the hot-forming temperature the steel flat product passes through at least one cold-forming step. 
     
     
         46 . The method according to  claim 31 , wherein before heating to the hot-forming temperature the Al coating applied onto the steel flat product has a thickness of 5-25 μm. 
     
     
         47 . The method according to  claim 31 , wherein before heating to the hot-forming temperature the Zn coating applied onto the Al coating has a thickness of 2-10 μm. 
     
     
         48 . The method according to  claim 31 , wherein before heating to the hot-forming temperature a 2-5 μm thick alloy barrier layer containing Al, Si, and Fe is present between the steel flat product and the Al coating. 
     
     
         49 . The method according to  claim 46 , wherein the total thickness of the metal coating present on the steel flat product before heating to the hot-forming temperature is 7-35 μm. 
     
     
         50 . The method according to  claim 31 , wherein the finish-formed steel component has a base layer directly on the steel flat product from which the steel component is formed, predominantly consisting of Al and additional contents of Fe, Zn, and Si, and on the base layer, a top layer predominantly consisting of Zn and additional contents of Al, Si, and Fe. 
     
     
         51 . The method according to  claim 50 , wherein the base layer has at least 30% wt. Al, at least 20% wt. Fe and at least 3% wt. Si. 
     
     
         52 . The method according to  claim 50 , wherein the top layer has at least 60% wt. Zn, at least 5% wt. Al, up to 10% wt. Fe and up to 10% wt. Si. 
     
     
         53 . The method according to  claim 50 , wherein the thickness of the base layer is 15-25 μm. 
     
     
         54 . The method according to  claim 50 , wherein the thickness of the top layer is 3-10 μm. 
     
     
         55 . The method according to  claim 31 , wherein the steel flat product is produced from a manganese boron steel. 
     
     
         56 . A steel component produced by forming using at least one hot-forming step comprising a steel flat product produced from a low-alloy heat-treated steel and coated with a metallic coating which protects against corrosion, wherein the metallic coating is formed by a base layer lying on the steel flat product and by a top layer lying on the base layer, and the base layer contains at least 30% wt. Al, at least 20% wt. Fe, at least 3% wt. Si and at most 30% wt. Zn, and the top layer has at least 60% wt. Zn, at least 5% wt. Al, up to 10% wt. Fe and up to 10% wt. Si. 
     
     
         57 . The steel component according to  claim 56 , wherein the thickness of the base layer is 10-50 μm. 
     
     
         58 . The steel component according to  claim 56 , wherein the thickness of the top layer is 5-20 μm. 
     
     
         59 . The steel component according to  claim 56 , wherein the steel flat product is produced from a manganese boron steel. 
     
     
         60 . The method according to  claim 47 , wherein the total thickness of the metal coating present on the steel flat product before heating to the hot-forming temperature is 7-35 μm. 
     
     
         61 . The method according to  claim 48 , wherein the total thickness of the metal coating present on the steel flat product before heating to the hot-forming temperature is 7-35 μm.