Method for producing a high-strength steel strip with improved properties for further processing, and a steel strip of this type

Abstract

A steel strip is produced by melting a steel melt containing (In wt. %): C: 0.1 to <0.3; Mn: 4 to <8; Al: >1 to 2.9; P: <0.05; S: <0.05; N: <0.02; remainder iron including unavoidable steel-associated elements. The steel melt is cast to form a pre-strip or to form a slab and heated to a rolling temperature of 1050 to 1250° C. or in-line rolling out of the casting heat. The pres-strip or slab is hot rolled into a hot strip having a thickness of 12 to 0.8 mm, at a final rolling temperature of 1050 to 800° C. The hot strip is reeled at a temperature of more than 200 to 800° C., pickled, annealed for an annealing time of 1 min to 48 h and at a temperature of 540 to 840° C., and cold rolled at room temperature or elevated temperature in at least one rolling pass.

What is claimed is: 
     
         1 .- 18 . (canceled) 
     
     
         19 . A method for producing an ultra high strength steel strip having a TRIP/TWIP effect, comprising:
 melting a steel melt containing (in wt. %): C: 0.1 to <0.3; Mn: 4 to <8; Al: >1 to 2.9; P: <0.05; S: <0.05; N: <0.02; with the remainder being iron including unavoidable steel-associated elements, in a blast furnace process or electric are furnace process;   casting the steel melt to form a pre-strip by a horizontal or vertical strip casting process approximating a final dimension or casting the steel melt to form a slab or thin slab by a horizontal or vertical slab or thin slab casting process;   heating to a rolling temperature of 1050 to 1250° C. or in-line rolling out of the casting heat;   hot rolling the pre-strip or the slab or the thin slab to form a hot strip having a thickness of 12 to 0.8 mm, at a final rolling temperature of 1050 to 800° C.;   reeling the hot strip at a temperature of more than 200 to 800° C.;   pickling the hot strip;   annealing the hot strip in a continuous or discontinuous annealing installation for an annealing time of 1 min to 48 h and at a temperature of 540 to 840° C.; and   cold rolling the hot strip at room temperature or elevated temperature in one or a plurality of rolling passes.   
     
     
         20 . The method of  claim 19 , further comprising adding to the steel melt by alloying at least one element in wt. % selected from the group consisting of Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01. 
     
     
         21 . The method of  claim 19 , further comprising subjecting the steel melt in blast furnace process or electric arc furnace process to a vacuum treatment. 
     
     
         22 . The method of  claim 19 , further comprising electrolytically galvanising or hot-dip galvanising the steel strip or applying another organic or inorganic coating. 
     
     
         23 . The method of  claim 19 , wherein the hot strip is cold rolled at a temperature of 60 to 450° C. 
     
     
         24 . The method of  claim 19 , wherein during cold rolling in a plurality of rolling passes the hot strip is selectively intermediately heated or cooled to a temperature of 60 to 450° C. between the rolling passes. 
     
     
         25 . The method of  claim 19 , further comprising, after cold rolling at room temperature or elevated temperature, annealing the steel strip in a continuous annealing installation for an annealing time of 1 to 15 min and at a temperature of 720° C. to 840° C., or by a discontinuous annealing installation for an annealing time of 30 min to 48 h and at a temperature of 550° C. to 820° C. 
     
     
         26 . The method of  claim 19 , further comprising, after undergoing annealing, cooling the steel strip to a temperature of below 250° C. to room temperature, subsequently reheating the steel strip to a temperature of 300 to 450° C., maintaining the steel strip at the temperature of 300 to 450° C. for up to 5 min, and subsequently cooling the steel strip to room temperature. 
     
     
         27 . The method of  claim 19 , further comprising temper-rolling the steel strip after cold rolling. 
     
     
         28 . The method of  claim 22 , further comprising applying a further coating on an organic or inorganic basis upon the steel strip after electrolytic galvanising or hot-dip galvanising. 
     
     
         29 . The method of  claim 19 , further comprising cold forming or warm forming the steel strip into a structural component. 
     
     
         30 . The method of  claim 29 , wherein warm forming of the steel strip is executed at a temperature of 60 to 450° C. 
     
     
         31 . A ultra high strength steel strip having a TRIP/TWIP effect, said steel strip comprising:
 an alloy composition containing (in wt. %): C: 0.1 to <0.3; Mn: 4 to <8; Al: >1 to 2.9; P: <0.05; S: <0.05; N: <0.02; with the remainder being iron including unavoidable steel-associated elements; and   a microstructure (in vol. %) including as phase components 10 to 80% austenite, 10 to 90% martensite, with the remainder being ferrite and bainite having a proportion together of less than 20%.   
     
     
         32 . The steel strip of  claim 31 , further comprising at least one element in wt. % selected from the group consisting of Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01. 
     
     
         33 . The steel strip of  claim 31 , wherein a sum of the contents of Mn and Al (in wt. %) satisfies a following requirement: 6.5<Mn+Al<10. 
     
     
         34 . The steel strip of  claim 31 , wherein a proportion of at least 20% of the martensite is present as annealed martensite. 
     
     
         35 . The steel strip of  claim 31 , wherein a proportion of >10% of the austenite is present in the form of annealing or deformation twins. 
     
     
         36 . The steel strip of  claim 31 , having an average grain size of the phase components:
 austenite: less than 500 nm,   martensite, ferrite, bainite: less than 650 nm.   
     
     
         37 . The steel strip of  claim 31 , having a tensile strength Rm of 1100 to 2200 MPa, a 0.2% elasticity limit Rp0.2 of 300 to 1550 MPa, and an elongation at fracture A80 of more than 4 to 41%. 
     
     
         38 . The steel strip of  claim 31 , wherein the steel strip is defined by the following dependencies of tensile strength Rm in MPa and elongation at fracture A80 in %:
 Rm of over 1100 to 1200 MPa: Rm×A80≥25000 up to 45000 MPa %   Rm of over 1200 to 1400 MPa: Rm×A80≥20000 up to 42000 MPa %   Rm of over 1400 to 1800 MPa: Rm×A80≥10000 up to 40000 MPa %   Rm of over 1800 MPa: Rm×A80≥7200 up to 20000 MPa %.   
     
     
         39 . The steel strip of  claim 31 , further comprising a galvanisation coat formed by galvanising the steel strip, and a further metallic, Inorganic or organic coating on the galvanisation coat. 
     
     
         40 . The steel strip of  claim 31 , produced by a method comprising:
 melting a steel melt containing (in wt. %): C: 0.1 to <0.3; Mn: 4 to <8; Al: >1 to 2.9; P: <0.05; S: <0.05; N: <0.02; with the remainder being iron including unavoidable steel-associated elements, in a blast furnace process or electric arc furnace process with optional vacuum treatment of the melt,   casting the steel melt to form a pre-strip by a horizontal or vertical strip casting process approximating a final dimension or casting the steel melt to form a slab or thin slab by a horizontal or vertical slab or thin slab casting process,   heating to a rolling temperature of 1050 to 1250° C. or In-line rolling out of the casting heat,   hot rolling the pre-strip or the slab or the thin slab to form a hot strip having a thickness of 12 to 0.8 mm, at a final rolling temperature of 1050 to 800° C.,   reeling the hot strip at a temperature of more than 200 to 800° C.,   pickling the hot strip,   annealing the hot strip in a continuous or discontinuous annealing installation for an annealing time of 1 min to 48 h and at a temperature of 540 to 840° C., and   cold rolling the hot strip at room temperature or elevated temperature in one or a plurality of rolling passes.