High strength cold rolled steel sheet and method for manufacturing the same

Abstract

The present invention relates to a high strength cold rolled steel sheet consisting of 0.015% or less of C, 1.5% or less of Si, 0.4 to 3% of Mn, 0.15% or less of P, 0.02% or less of S, 0.1 to 1% of sol.Al, 0.01% or less of N, 0.2% or less of Ti, by mass %, and the balance of Fe and inevitable impurities. In this steel sheet, 1≦([Ti]/48)/([C]/12+[N]/14) is satisfied, in which [M] represents the content of the element M. Since having the superior deep drawability and the TS of 340 to 590 MPa, the high strength cold rolled steel sheet of the present invention is preferably used for automobiles parts difficult to be press formed, such as a side outer panel and a door inner panel.

1 . A high strength cold rolled steel sheet consisting of 0.015% or less of C, 1.5% or less of Si, 0.4 to 3% of Mn, 0.15% or less of P, 0.02% or less of S, 0.1 to 1% of sol.Al, 0.01% or less of N, 0.2% or less of Ti, by mass %, and the balance of Fe and inevitable impurities, 
 wherein the following equation (1) is satisfied;      1≦([Ti]/48)/([C]/12+[N]/14)  (1),    where [M] represents the content (mass %) of the element M.    
   
   
       2 . The high strength cold rolled steel sheet according to  claim 1 , wherein the content of sol.Al is 0.2 to 0.7%.  
   
   
       3 . The high strength cold rolled steel sheet according to  claim 1 , wherein the following equation (2) is satisfied;  
       0.3≦[Si]+10×[P]≦1.4  (2),  
     where [M] represents the content (mass %) of the element M.  
   
   
       4 . The high strength cold rolled steel sheet according to  claim 2 , wherein the following equation (2) is satisfied;  
       0.3≦[Si]+10×[P]≦1.4  (2),  
     where [M] represents the content (mass %) of the element M.  
   
   
       5 . The high strength cold rolled steel sheet according to  claim 1 , further comprising, by mass %, 0.002 to 0.02% of Nb, wherein the following equation (3) is satisfied;  
       1≦([Nb]/93+[Ti]/48)/([C]/12+[N]/14)  (3),  
     where [M] represents the content (mass %) of the element M.  
   
   
       6 . The high strength cold rolled steel sheet according to  claim 4 , further comprising, by mass %, 0.002 to 0.02% of Nb, wherein the following equation (3) is satisfied;  
       1≦([Nb]/93+[Ti]/48)/([C]/12+[N]/14)  (3),  
     where [M] represents the content (mass %) of the element M.  
   
   
       7 . The high strength cold rolled steel sheet according to  claim 1 , further comprising, by mass %, 0.0001 to 0.003% of B.  
   
   
       8 . The high strength cold rolled steel sheet according to  claim 6 , further comprising, by mass %, 0.0001 to 0.003% of B.  
   
   
       9 . The high strength cold rolled steel sheet according to  claim 1 , further comprising, by mass %, at least one element selected from the group consisting of 0.03 to 0.5% of Cu, 0.03 to 0.5% of Ni, 0.03 to 0.5% of Cr, 0.05 to 0.3% of Mo, and 0.005 to 0.5% of V.  
   
   
       10 . The high strength cold rolled steel sheet according to  claim 8 , further comprising, by mass %, at least one element selected from the group consisting of 0.03 to 0.5% of Cu, 0.03 to 0.5% of Ni, 0.03 to 0.5% of Cr, 0.05 to 0.3% of Mo, and 0.005 to 0.5% of V.  
   
   
       11 . The high strength cold rolled steel sheet according to  claim 1 , further comprising, by mass %, at least one element selected from the group consisting of 0.002 to 0.2% of Sb and 0.002 to 0.2% of Sn, wherein the following equation (4) is satisfied;  
       0.002≦[Sb]+[Sn]/2≦0.2  (4),  
     where [M] represents the content (mass %) of the element M.  
   
   
       12 . The high strength cold rolled steel sheet according to  claim 10 , further comprising, by mass %, at least one element selected from the group consisting of 0.002 to 0.2% of Sb and 0.002 to 0.2% of Sn, wherein the following equation (4) is satisfied;  
       0.002≦[Sb]+[Sn]/2≦0.2  (4),  
     where [M] represents the content (mass %) of the element M.  
   
   
       13 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 1  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       14 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 2  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       15 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 3  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       16 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 4  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       17 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 5  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       18 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 6  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       19 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 7  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       20 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 8  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       21 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 9  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       22 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 10  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       23 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 11  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.    
   
   
       24 . A method for manufacturing a high strength cold rolled steel sheet, comprising the steps of: 
 heating a slab having the chemical composition according to  claim 12  at 1,080 to 1,350° C.;    hot rolling the heated slab at a finishing temperature between (the Ar3 transformation temperature−20)° C. and (the Ar3 transformation temperature+150)° C. into a hot rolled steel sheet;    coiling the hot rolled steel sheet at a coiling temperature CT which satisfies the following equation (5) or (6);    cold rolling the hot rolled steel sheet with a reduction of 50 to 90% into a cold rolled steel sheet; and    continuously annealing the cold rolled steel sheet at a temperature of 750 to 870° C. or box annealing the cold rolled steel sheet at a temperature of 600 to 750° C.;      480≦CT≦580+0.17/{([Ti]+0.08 ×[sol .Al])×[P]}  (5), and  480≦CT≦580+0.17/{(0.6×[Nb]+[Ti]+0.08 ×[sol .Al])×[P]}  (6),    where [M] represents the content (mass %) of the element M.