Steel sheet excellent in fine blanking performance and manufacturing method of the same

Abstract

A steel sheet excellent in FB performance and also excellent in fabrication performance after FB working and a manufacturing method of the same are provided. The steel sheet is a steel sheet having a composition containing from 0.1 to 0.5% of C, not more than 0.5% of Si and from 0.2 to 1.5% of Mn in terms of % by mass, with P and S being adjusted at proper ranges and having a structure having a ferrite having an average grain size of more than 10 μm and less than 20 μm and a cementite present in the ferrite grain having an average particle size of from 0.3 to 1.5 μm. In this way, the steel sheet becomes a steel sheet excellent in FB performance, mold life and performance (side bend elongation) after FB working.

1 - 6 . (canceled) 
   
   
       7 . A steel sheet excellent in fine blanking performance, having a composition comprising from 0.1 to 0.5% of C, not more than 0.5% of Si, from 0.2 to 1.5% of Mn, not more than 0.03% of P and not more than 0.02% of S in terms of % by mass, with the remainder being Fe and unavoidable impurities and having a structure mainly composed of ferrite and cementite, wherein said ferrite has an average grain size of exceeding 10 μm and less than 20 μm, and of said cementite, cementite present in the ferrite grain has an average particle size of from 0.3 to 1.5 μm. 
   
   
       8 . The steel sheet according to  claim 7 , wherein the composition further comprises not more than 0.1% of Al in terms of % by mass. 
   
   
       9 . The steel sheet according to  claims 7 , wherein the composition further comprises one or more members selected from the group consisting of not more than 3.5% of Cr, not more than 0.7% of Mo, not more than 3.5% of Ni, from 0.01 to 0.1% of Ti and from 0.0005 to 0.005% of B in terms of % by mass. 
   
   
       10 . The steel sheet according to  claims 8 , wherein the composition further comprises one or more members selected from the group consisting of not more than 3.5% of Cr, not more than 0.7% of Mo, not more than 3.5% of Ni, from 0.01 to 0.1% of Ti and from 0.0005 to 0.005% of B in terms of % by mass. 
   
   
       11 . A method of manufacturing a steel sheet excellent in fine blanking performance including successively applying hot rolling by heating and rolling a raw steel material to form a hot rolled sheet and hot rolled sheet annealing by applying annealing to the hot rolled sheet, wherein the raw steel material has a composition comprising from 0.1 to 0.5% of C, not more than 0.5% of Si, from 0.2 to 1.5% of Mn, not more than 0.03% of P and not more than 0.02% of S in terms of % by mass, with the remainder being Fe and unavoidable impurities; said hot rolling is a treatment in which a total reduction ratio in a temperature region of from 800 to 950° C. in finish rolling is at 25% or more, a termination temperature of finish rolling is from 800 to 950° C., after completion of the finish rolling, cooling is carried out at an average cooling rate of 50° C./s or more and less than 120° C./s, the cooling is stopped at a temperature from 500 to 700° C., and coiling is carried out at from 450 to 600° C.; and said hot rolled sheet annealing is carried out at an annealing temperature from 600 to 720° C. 
   
   
       12 . The method according to  claim 11 , wherein the composition further comprises not more than 0.1% of Al in terms of % by mass. 
   
   
       13 . The method according to  claim 11 , wherein the composition further comprises one or more members selected from the group consisting of not more than 3.5% of Cr, not more than 0.7% of Mo, not more than 3.5% of Ni, from 0.01 to 0.1% of Ti and from 0.0005 to 0.005% of B in terms of % by mass. 
   
   
       14 . The method according to  claim 12 , wherein the composition further comprises one or more members selected from the group consisting of not more than 3.5% of Cr, not more than 0.7% of Mo, not more than 3.5% of Ni, from 0.01 to 0.1% of Ti and from 0.0005 to 0.005% of B in terms of % by mass.