Formable lightweight steel having improved mechanical properties and method for producing semi-finished products from said steel

Abstract

The invention relates to a formable lightweight steel having improved mechanical properties and a high resistance to delayed hydrogen-induced cracking formation and hydrogen embrittlement comprising the following elements (in wt. %): C 0.02 to ≤1.0; Mn 3 to 30; Si≤4; P max. 0.1; S max. 0.1; N max. 0.03; Sb 0.003 to 0.8, particularly advantageously to 0.5, as well as at least one or more of the following carbide-forming elements in the specified proportions (in wt. %): Al≤15; Cr>0.1 to 8; Mo 0.05 to 2; Ti 0.01 to 2; V 0.005 to 1; Nb 0.005 to 1; W 0.005 to 1; Zr 0.001 to 0.3; with the remainder consisting of iron including the usual steel-accompanying elements, with the optional addition of the following elements, in wt. %: max. 5 Ni, max. 10 Co, max. 0.005 Ca, max. 0.01 B and 0.05 to 2 Cu. The invention also relates to a method for producing the said lightweight steel.

1 .- 8 . (canceled) 
     
     
         9 . A formable lightweight steel having improved mechanical property and high resistance to delayed hydrogen-induced crack formation and hydrogen embrittlement, the formable lightweight steel comprising the following elements, in wt.-%:
 C 0.02 to ≤1.0   Mn 3 to 30   Si≤4   P max. 0.1   S max. 0.1   N max. 0.03   Sb 0.003 to 0.8,   and at least one carbide-forming element selected from the group consisting of, in wt.-%   Al≤15   Cr>0.1 to 8   Mo 0.05 to 2   Ti 0.01 to 2   V 0.005 to 1   Nb 0.005 to 1   W 0.005 to 1   Zr 0.001 to 0.3,   with the remainder being iron, including typical steel-associated elements.   
     
     
         10 . The formable lightweight steel of  claim 9 , wherein a proportion of Sb is 0.003 to 0.5. 
     
     
         11 . The formable lightweight steel of  claim 9 , further comprising at least one element, in wt-%: Ni max. 5; Co max. 10; Ca max. 0.005; B max. 0.01; and Cu 0.05 to 2. 
     
     
         12 . The formable lightweight steel of  claim 9 , wherein a ratio Sb/C is less than or equal to 1.5. 
     
     
         13 . The formable lightweight steel of  claim 9 , wherein the elements have the following proportions, in wt-%:
 C is 03 to 0.5   Mn 3 to 10   Al 0.1 to 4   Si 0.1 to 3   Sb 0.005 to 0.3   Cr>0.1 to 5   V 0.005 to 1,   wherein the steel has a product of tensile strength and elongation at facture of at least 20,000 MPa % and a tensile strength of at least 800 MPa.   
     
     
         14 . The formable lightweight steel of  claim 9 , wherein the elements have the following proportions, in wt-%:
 C 0.1 to 0.35   Mn 5 to 9   Al 1 to 3.5   Si 0.1 to 1   Sb 0.01 to 0.1   Cr 0.5 to 4   V 0.02 to 0.1,   wherein the steel has a product of tensile strength and elongation at facture of at least 20,000 MPa % and a tensile strength of at least 800 MPa.   
     
     
         15 . The formable lightweight steel of  claim 9 , wherein the elements have the following proportions, in wt.-%:
 C 0.4 to 0.9   Mn 12 to 18   Al 0.5 to 4   Si 0.5 to 3   Sb 0.005 to 0.4,   said at least one carbide-forming element being selected in the following proportions (in wt.-%):   Cr>0.1 to 4   Mo 0.05 to 1   Ti 0.01 to 0.1   V 0.005 to 0.3   Nb 0.005 to 0.3   W 0.005 to 0.5   Zr 0.001 to 0.3,   with the remainder being iron, including typical steel-associated elements, wherein the steel has a product of tensile strength and elongation at facture of at least 30,000 MPa % and a tensile strength of at least 800 MPa.   
     
     
         16 . The formable lightweight steel of  claim 9 , wherein the elements have the following proportions, in wt.-%:
 C 0.6 to 1.4   Mn 10 to 30   Al>4 to 15   Si 0.05 to 0.5   Sb 0.005 to 0.5,   said at least one carbide-forming element being selected in the following proportions (in wt.-%):   Cr>0.1 to 4   Mo 0.05 to 1   Ti 0.01 to 0.1   V 0.005 to 0.3   Nb 0.005 to 0.3   W 0.005 to 0.5   Zr 0.001 to 0.3,   with the remainder being iron, including typical steel-associated elements,   wherein the steel has finely distributed kappa-carbide precipitations and a product of tensile strength and elongation at facture of at least 30,000 MPa % and a yield strength of at least 700 MPa and a tensile strength of at least 800 MPa.   
     
     
         17 . A method for producing a formable lightweight steel having improved mechanical properties and a high resistance to delayed hydrogen-induced crack formation and hydrogen embrittlement, the formable lightweight steel comprising the following elements, in wt.-%:
 C 0.02 to ≤1.0   Mn 3 to 30   Si≤4   P max. 0.1   S max. 0.1   N max. 0.03   Sb 0.003 to 0.8;   and at least one carbide-forming element selected from the group consisting of, in wt.-%:   Al≤15;   Cr>0.1 to 8;   Mo 0.05 to 2;   Ti 0.01 to 2;   V 0.005 to 1   Nb 0.005 to 1   W 0.005 to 1   Zr 0.001 to 0.3,   with the remainder being iron, including typical steel-associated elements, the method comprising:
 casting the lightweight steel in a continuous casting process, a thin-slab casting process, to form a cast strip or a cast slab with a thickness of more than 5 mm, or a horizontal or vertical strip casting process approximating the final dimensions to form a cast strip with a thickness of at most 5 mm; 
 hot rolling the cast slab or cast strip with a thickness of more than 5 mm to a uniform thickness, or flexibly hot rolling the cast slab or cast strip to different thicknesses. 
   
     
     
         18 . The method of  claim 17 , further comprising:
 after hot-rolling, cold rolling the hot-rolled strip having the uniform thickness or cold rolling the cast strip, which has a thickness of at most 5 mm and is produced by a casting process approximating the final dimensions, to a uniform thickness or flexibly cold-rolling to different thicknesses.   
     
     
         19 . The method of  claim 17 , further comprising:
 after hot-rolling, annealing the hot-rolled strip or cold-rolled strip at an annealing temperature of 480 to 770° C. and an annealing duration of 1 minute to 48 hours.   
     
     
         20 . The method of  claim 18 , further comprising:
 after hot-rolling, annealing the hot-rolled strip or cold-rolled strip at an annealing temperature of 480 to 770° C. and an annealing duration of 1 minute to 48 hours.   
     
     
         21 . The method of  claim 17 , further comprising:
 after hot-rolling, cold-rolling the cast strip, which has a thickness of at most 5 mm and is produced by a casting process approximating the final dimensions, to a uniform thickness or flexibly cold-rolling the cast strip to different thicknesses and then annealing the cold strip with the following parameters: annealing temperature: 480 to 770° C., annealing duration: 1 minute to 48 hours.   
     
     
         22 . The method of  claim 17 , wherein, when the steel has a proportion, in wt-%, of Al>1, the annealing temperature is 670 to 770° C. and the annealing duration is 1 minute to 12 hours.