Producing a hardened steel product

Abstract

Producing a hardened steel product can comprise providing a steel substrate of a hardenable steel; coating the steel substrate with an aluminum precoating, wherein the precoating is applied to the steel substrate with a thickness of at least 34 μm; flexible rolling the pre-coated steel substrate to produce a variable thickness along the length of the precoated steel substrate, wherein the precoating is rolled out to a reduced first thickness of less than 33 μm in thinner first portions and to a reduced second thickness thicker than the reduced first thickness in thicker second portions; working out a blank from the flexibly rolled steel substrate; heating the blank to austenitizing temperature, wherein diffusion processes take place between the base material and the precoating; and hot forming the heated blank, wherein the heated blank is formed and rapidly cooled such that a hardened steel product with coating is produced.

1 .- 15 . (canceled) 
     
     
         16 . A method for producing a hardened steel product, comprising:
 providing a steel substrate having a base material of a hardenable steel;   coating the steel substrate with an aluminum-containing precoating, wherein the precoating is applied to the steel substrate with a thickness of at least 34 micrometers;   flexible rolling of the precoated steel substrate, wherein successive portions of the precoated steel substrate are rolled out to different degrees, wherein through the flexible rolling the precoating obtains in thinner first portions of the precoated steel substrate a reduced first thickness of less than 33 micrometers, and in thicker second portions of the precoated steel substrate a reduced second thickness which is thicker than the reduced first thickness;   working a blank from the flexibly rolled steel substrate;   heating the blank such that the base material of the blank is at least partially austenitized, wherein diffusion processes take place between the base material and the precoating through the heating; and   hot forming the heated blank, wherein the heated blank is formed and rapidly cooled such that a hardened steel product with coating is produced.   
     
     
         17 . The method according to  claim 16 ,
 wherein the precoating is applied to the steel substrate with a thickness of at least 36 micrometers.   
     
     
         18 . The method according to  claim 16 ,
 wherein the precoating obtains in the thinner first portions a reduced first thickness of less than 20 micrometers by the flexible rolling.   
     
     
         19 . The method according to  claim 16 ,
 wherein the precoating obtains in the thicker second portions a reduced second thickness of more than 33 micrometers by the flexible rolling.   
     
     
         20 . The method according to  claim 16 ,
 wherein the coating is formed from the precoating through the heating and hot forming, with a first end thickness in the thinner first portions which is greater than the reduced first thickness and is between 15 to 50 micrometers, and   with a second end thickness in the thicker second portions which is greater than the reduced second thickness and is between 30 to 60 micrometers.   
     
     
         21 . The method according to  claim 16 ,
 wherein the coating of the hardened steel product is formed with a final thickness ratio of a first final thickness to a second final thickness being greater than an intermediate thickness ratio of the reduced first thickness to the reduced second thickness prior to hot forming.   
     
     
         22 . The method according to  claim 16 ,
 wherein steel substrate with an initial thickness of 1.0 to 4.0 mm is used.   
     
     
         23 . The method according to  claim 16 ,
 wherein the flexible rolling is carried out with rolling degrees of at least 1% and at most 60% starting from the initial thickness of the steel substrate.   
     
     
         24 . The method according to  claim 16 ,
 wherein the coating is applied to the steel substrate by hot-dip coating.   
     
     
         25 . The method according to  claim 24 ,
 wherein the steel substrate is heated in the coating device after application of the precoating in order to achieve prediffusion between the precoating and the steel substrate.   
     
     
         26 . The method according to  claim 16 ,
 wherein the steel substrate is a hardenable steel which contains the following proportions of alloying elements, respectively in percent by weight:   carbon (C) with more than 0.15% and less than 0.5%;   manganese (Mn) with more than 0.5% and less than 5.0%;   aluminum (Al) with less than 0.1%;   silicon (Si) with more than 0.1% and less than 0.9%;   chromium (Cr) with more than 0.01% and less than 1.0%;   tital (Ti) with less than 0.2%;   boron (B) with more than 0.0005 and less than 0.080%;   phosphorus (P) with less than 0.1%;   sulfur (S) with less than 0.05%;   optionally other alloying elements with a total content of up to 1.55%;   the rest iron (Fe) and unavoidable impurities.   
     
     
         27 . The method according to  claim 26 ,
 wherein the optionally further alloying element contain at least one of:   copper (Cu) with at most 0.1%;   nickel (Ni) with at most 0.1%;   niobium (Nb) with at most 0.1%;   molybdenum (Mo) with at most 1.0%;   vanadium (V) with at most 0.25%;   respectively in percent by weight.   
     
     
         28 . The method according to  claim 16 ,
 wherein the precoating contains at least 85% by weight of aluminum, and optionally 5 to 15% by weight of silicon.   
     
     
         29 . The method according to  claim 16 ,
 wherein a metal oxide layer is formed on the surface of the coated steel substrate before hot forming.   
     
     
         30 . The method according to  claim 16 ,
 wherein the blank is heated for austenitizing at a heating rate of more than 12 K/sec at least until a temperature of 700° C. is reached.