Method for thermally treating a flat steel product, thermally treated flat steel product and use thereof

Abstract

“A method for thermally treating a flat steel product, a thermally treated flat steel product and use thereof. The method includes providing a flat steel product with a structure with a first hardness. The flat product is heated at least in sections to an austenitizing temperature. The heated flat product is cooled at least in sections so that a structure with a second hardness is formed within the flat product at least in sections, the second hardness having a higher level of hardness in comparison to the structure with the first hardness. The heating and the cooling down of the flat product are coordinated with each other such that the structure with the second hardness is formed across the thickness of the flat product and at least in one of said sections, the structure with the first hardness remains constant across the thickness of the flat product.”

1 .- 19 . (canceled) 
     
     
         20 . A method for thermally treating a flat steel product comprising the following steps:
 providing a flat steel product with a structure with a first hardness,   heating the flat product at least in sections to an austenitizing temperature, and   cooling the flat product heated at least in sections so that a structure with a second hardness is formed within the flat product at least in sections, the second hardness having a higher level of hardness in comparison to the structure with the first hardness,   wherein the heating and the cooling down of the flat product are coordinated with each other such that the structure with the second hardness is formed across the thickness of the flat product in sections and, at least in one of said sections, the structure with the first hardness remains constant across the thickness of the flat product.   
     
     
         21 . The method of  claim 20 , wherein the heating takes place at least on one side with the use of at least one heat source, wherein the structure with the second hardness is at least formed within one edge section of the flat product. 
     
     
         22 . The method of  claim 20 , wherein at least one inductor is used as a heat source. 
     
     
         23 . The method of  claim 20 , wherein at least one edge section of the flat steel product is heated to at least a temperature of at least A c3 +20 K during the heating process and is held at this temperature for at least 1 s up to a maximum of 60 s. 
     
     
         24 . The method of  claim 20 , wherein the cooling takes place by quenching the flat product with water. 
     
     
         25 . The method of  claim 20 , wherein the heating takes place on both sides with the use of at least one heat source respectively, wherein the structure with the second hardness is formed in both edge sections of the flat product or an edge section with a structure with the second hardness is formed on one side of the flat product and an edge section with a structure with a third hardness is formed on the other side of the flat product, wherein the structure with the third hardness has a lower level of hardness than the structure with the second hardness and a higher level of hardness than the structure with the first hardness. 
     
     
         26 . The method of  claim 25 , wherein at least between an edge section with the structure with the second hardness and/or third hardness and the section with the structure with the first hardness, an annealing section with a structure with a fourth hardness is formed, which has a lower level of hardness than the section with the structure with the first hardness. 
     
     
         27 . The method of  claim 26 , wherein at least in one of the edge sections with the structure with the second hardness and/or third hardness, a decarburized edge layer or an edge layer with a fifth hardness and a lower level of hardness in comparison to the edge section with the structure with the second hardness and/or third hardness is formed. 
     
     
         28 . The method of  claim 20 , including forming across the thickness of the flat product, a symmetric or asymmetric hardness profile. 
     
     
         29 . The method of  claim 20 , wherein the flat steel product consists of the following components in % by weight: 
       
         
           
                 
                 
               
                     
                     
                 
                     
                   0.15 ≤ C ≤ 0.6, 
                 
                     
                   0.1 ≤ Si ≤ 1.2, 
                 
                     
                   0.3 ≤ Mn ≤ 1.8, 
                 
                     
                   0.1 ≤ Cr ≤ 1.8, 
                 
                     
                   0.05 ≤ Mo ≤ 0.6, 
                 
                     
                   0.05 ≤ Ni ≤ 3.0, 
                 
                     
                   0.0005 ≤ B ≤ 0.01, 
                 
                     
                   Al ≤ 0.15, 
                 
                     
                   Ti ≤ 0.04, 
                 
                     
                   P ≤ 0.04, 
                 
                     
                   S ≤ 0.03, 
                 
                     
                   N ≤ 0.03, 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         wherein the remainder is iron and impurities. 
       
     
     
         30 . The method of  claim 20 , including forming and/or cutting the flat product into a final product. 
     
     
         31 . A thermally treated flat steel product made according to the method of  claim 20 , wherein within the flat product, a structure is formed with the second hardness in sections across the thickness of the flat product and, at least in one section, a structure with the first hardness is formed across the thickness of the flat product, wherein the structure with the second hardness has a higher level of hardness in comparison to the structure with the first hardness and is thermally treated. 
     
     
         32 . The flat steel product of  31 , wherein the structure with the second hardness is formed in an edge section of the flat product, wherein the layer thickness of the edge section is at least 5% up to a maximum of 80% of the total thickness of the flat product and the remaining thickness of the total thickness of the flat product consists of the section with the structure with the first hardness. 
     
     
         33 . The flat steel product of  claim 31 , the structure with the second hardness is formed within both edge sections of the flat product or one edge section with a structure with the second hardness is formed on one side of the flat product and one edge section with a structure with a third hardness is formed on the other side of the flat product, wherein the structure with the third hardness has a lower level of hardness than the structure with the second hardness, and a higher level of hardness than the structure with the first hardness, wherein the layer thickness of the edge section varies between at least 5% and a maximum of 45% of the total thickness of the flat product respectively and the remaining thickness is formed by the section with the structure with the first hardness. 
     
     
         34 . The flat steel product of  claim 33 , wherein the flat product has a hardness difference of at least 100 HV10 between the at least one edge section with the structure with the second hardness and/or third hardness and the section with the structure with the first hardness. 
     
     
         35 . The flat steel product of  claim 33 , wherein the flat product at least between one edge section with the structure with the second hardness and/or third hardness and the section with the structure with the first hardness comprises an annealing section with a structure with a fourth hardness, which has at least a 10 HV10 lower level of hardness in comparison with the section with the structure with the first hardness. 
     
     
         36 . The flat steel product of  claim 35 , wherein the flat product at least in one of the edge sections with the structure with the second hardness and/or third hardness comprises a decarburized edge layer or an edge layer with a structure with a fifth hardness, which has a lower level of hardness in comparison to the edge section with the structure with the second hardness and/or third hardness. 
     
     
         37 . The flat steel product of  claim 31 , wherein the flat product has a total thickness between 3 and 80 mm. 
     
     
         38 . The flat steel product of  claim 31 , wherein the flat product has a total thickness between 6 and 20 mm.