Cold-rolled steel strip and hot-dip coated cold-rolled steel strip for use as building material and manufacturing method thereof

Abstract

A cold-rolled steel strip or hot-dip coated cold-rolled steel strip for use as a fire-proof building member has composition consisting of 0.01-0.25 wt. % C, up to 1.5 wt. % Si, 0.05-2.5 wt. % Mn, up to 0.1 wt. % P, no more than 0.02 wt. % S, 0.005-0.1 wt. % Al, 0.05-1.0 wt. % Mo, optionally 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W, optionally one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B and the balance being essentially Fe except inevitable impurities. The cold-rolled steel strip is manufactured by hot-rolling, acid-pickling, cold-rolling and then annealing at a temperature above its recrystallization temperature but below 950° C. The hot-dip coated cold-rolled steel strip is manufactured in the same way but in-line heating a cold-rolled steel strip at a temperature above its recrystallization temperature but below 950° C. and then immersing it into a coating bath. The annealed or hot-dip coated steel strip may be further cold-rolled with such a slight duty to induce a plastic strain of 1-5%.

What is claimed is;  
     
         1 . A cold-rolled steel strip for use as a fire-proof building member consisting of 0.01-0.25 wt. % C, up to 1.5 wt. % Si, 0.05-2.5 wt. % Mn, up to 0.1 wt. % P, no more than 0.02 wt. % S, 0.005-0.1 wt. % Al, 0.05-1.0 wt. % Mo and the balance being essentially Fe except inevitable impurities.  
     
     
         2 . The cold-rolled steel strip defined in    claim 1   , which further contains 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W.  
     
     
         3 . The cold-rolled steel strip defined in    claim 1   , which further contains one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B.  
     
     
         4 . The cold-rolled steel strip defined in    claim 1   , which further contains 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W, and one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B.  
     
     
         5 . A hot-dip coated cold-rolled steel strip for use as a fire-proof building member consisting of 0.01-0.25 wt. % C, up to 1.5 wt. % Si, 0.05-2.5 wt. % Mn, up to 0.1 wt. % P, no more than 0.02 wt. % S, 0.005-0.1 wt. % Al, 0.05-1.0 wt. % Mo and the balance being essentially Fe except inevitable impurities.  
     
     
         6 . The hot-dip coated cold-rolled steel strip defined in    claim 5   , which further contains 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W.  
     
     
         7 . The hot-dip coated cold-rolled steel strip defined in    claim 5   , which further contains one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B.  
     
     
         8 . The hot-dip coated cold-rolled steel strip defined in    claim 5   , which further contains 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W, and one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Or and 0.0003-0.003 wt. % B.  
     
     
         9 . A method of manufacturing a cold-rolled steel strip for use as a fire-proof building member, comprising the steps of: 
 preparing a slab having composition consisting of 0.01-0.25 wt. % C, up to 1.5 wt. % Si, 0.05-2.5 wt. % Mn, up to 0.1 wt. % P, no more than 0.02 wt. % S, 0.005-0.1 wt. % Al, 0.05-1.0 wt. % Mo, optionally 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W, optionally one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B and the balance being essentially Fe except inevitable impurities;    heating said slab at 1000-1250° C.;    hot-rolling the heated slab at a finishing temperature of 800-950° C.;    coiling the hot-rolled steel strip at 400-700° C.;    acid pickling the hot-rolled steel strip;    cold-rolling the pickled steel strip at a reduction ratio of 40-90%;    annealing the cold-rolled steel strip at a temperature above its recrystallization temperature but below 950° C.; and    optionally cold-rolling the annealed steel strip with such a slight duty to induce a plastic strain of 1-5% to said steel strip.    
     
     
         10 . The method defined in    claim 9   , wherein the cold-rolled steel strip is box-annealed or continuously annealed.  
     
     
         11 . A method of manufacturing a hot-dip coated cold-rolled steel strip for use as a fire-proof building member, comprising the steps of: 
 preparing a slab having composition consisting of 0.01-0.25 wt. % C, up to 1.5 wt. % Si, 0.05-2.5 wt. % Mn, up to 0.1 wt. % P, no more than 0.02 wt. % S, 0.005-0.1 wt. % Al, 0.05-1.0 wt. % Mo, optionally 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W, optionally one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B and the balance being essentially Fe except inevitable impurities;    heating said slab at 1000-1250° C.;    hot-rolling the heated slab at a finishing temperature of 800-950° C.;    coiling the hot-rolled steel strip at 400-700° C.;    acid pickling the hot-rolled steel strip;    cold-rolling the pickled steel strip at a reduction ratio of 40-90%;    in-line heating the cold-rolled steel strip at a temperature above its recrystallization temperature but below 950° C. in a continuous hot-dip coating installation;    immersing the in-line heated steel strip into a hot-dip coating bath; and    optionally cold-rolling the hot-dip coated steel strip with such a slight duty to induce a plastic strain of 1-5% to said steel strip.