Method for manufacturing flat steel products from boron microalloyed multi-phase steel

Abstract

A method, which allows high-tensile flat steel products to be manufactured with less effort includes a steel that forms a multi-phase microstructure and contains (in wt. %) 0.08-0.12% C, 1.70-2.00% Mn, up to 0.030% P, up to 0.004% S, up to 0.20% Si, 0.01-0.06% Al, up to 0.0060% N, 0.20-0.50% Cr, 0.010-0.050% Ti, 0.0010-0.0045% B, remainder iron and unavoidable impurities, being cast into a cast strip having a thickness of 1-4 mm. The cast strip is hot-rolled in-line into a hot-rolled strip having a thickness of 0.5-3.2 mm in a continuous process at a final hot-rolling temperature ranging from 800 to 1100° .C, the deformation degree being greater than 20%. The hot-rolled strip is coiled at a coiling temperature ranging from 250 to 570° C., so as to obtain a hot-rolled strip, which has a minimum tensile strength R m of 800 MPa at a minimum breaking elongation A 80 of 5%.

1 . Method for manufacturing flat steel products,
 wherein a steel that forms a multi-phase microstructure with the following composition (in wt. %)   C: 0.08-0.12%   Mn: 1.70-2.00%   P:≦0.030%   S:≦0.004%   Si:≦0.20%   Al: 0.01-0.06%   N:≦0.0060%   Cr: 0.20-0.50%   Ti: 0.010-0.050%   B: 0.0010-0.0045%   remainder iron and unavoidable impurities   is cast into a cast strip having a thickness of 1-4 mm,   wherein the cast strip is hot-rolled in-line into a hot-rolled strip having a thickness ranging from 0.5 to 3.2 mm in a continuous process at a final hot-rolling temperature ranging from 800 to 1100° C., the deformation degree being greater than 20%, and   wherein the hot-rolled strip is coiled at a coiling temperature ranging from 250 to 570° C.   so as to obtain a hot-rolled strip, which has a minimum tensile strength R m  of 800 MPa at a minimum breaking elongation A 80  of 5%.   
   
   
       2 . Method according to  claim 1 , wherein the width of the hot-rolled strip is greater than 1,200 mm. 
   
   
       3 . Method according to  claim 1 , wherein the thickness of the hot-rolled strip is 1.5 mm at most. 
   
   
       4 . Method according to  claim 1 , wherein the hot-rolled strip is cold-rolled into cold-rolled strip having a thickness of 0.5-1.4 mm. 
   
   
       5 . Method according to  claim 4 , wherein the cold-rolled strip is annealed at an annealing temperature of 750-850° C. 
   
   
       6 . Method according to  claim 4 , wherein a minimum tensile strength of the cold-rolled strip is 800 MPa. 
   
   
       7 . Method according to  claim 4 , wherein the cold-rolled strip has a minimum breaking elongation A 50  of 10%. 
   
   
       8 . Method according  claim 1 , wherein the hot-rolled strip is provided with a metallic coating. 
   
   
       9 . Method according to  claim 8 , wherein the metallic coating is a zinc coating. 
   
   
       10 . Method according to  claim 1 , wherein with a minimum breaking elongation A 80  of the obtained hot-rolled strip of 10%, the final hot-rolling temperature is 900-1020° C. and the coiling temperature is 420-490° C. 
   
   
       11 . Method according to  claim 1 , wherein with a minimum tensile strength R m  of the obtained hot-rolled strip of 1000 MPa, the final hot-rolling temperature is 900-1100° C. and the coiling temperature is 450-570° C. 
   
   
       12 . Method according to  claim 1 , wherein with a minimum tensile strength R m  of the obtained hot-rolled strip of 1200 MPa, the final hot-rolling temperature is 800-1000° C. and the coiling temperature is 250-550° C. 
   
   
       13 . Method according to  claim 4 , wherein the cold-rolled strip is provided with a metallic coating. 
   
   
       14 . Method according to  claim 13 , wherein the metallic coating is a zinc coating.