Steel sheet for warm press forming, warm-pressed member, and manufacturing methods thereof

Abstract

Provided are a steel sheet for warm press forming that can have high strength, good elongation, and thus improved crashworthiness after being warm pressed, and a warm-pressed member formed of the steel sheet, and manufacturing methods thereof. The steel sheet for warm press forming includes, by weight %, C: 0.01% to 0.5%, Si: 3.0% or less (excluding 0%), Mn: 3% to 15%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, Al: 3.0% or less (excluding 0%), N: 0.03% or less (excluding 0%), and the balance of Fe and inevitable impurities.

1 . A steel sheet for warm press forming, the steel sheet comprising, by weight %, C: 0.01% to 0.5%, Si: 3.0% or less (excluding 0%), Mn: 3% to 15%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, Al: 3.0% or less (excluding 0%), N: 0.03% or less (excluding 0%), and the balance of Fe and inevitable impurities. 
     
     
         2 . The steel sheet of  claim 1 , further comprising 0.001% to 2.0% of at east one selected from the group consisting of Cr, Mo, and W. 
     
     
         3 . The steel sheet of  claim 1 , further comprising 0.001% to 0.4% of at least one selected from the group consisting of Ti, Nb, Zr, and V. 
     
     
         4 . The steel sheet of  claim 1 , further comprising 0.005% to 2.0% of at least one of Cu and Ni. 
     
     
         5 . The steel sheet of  claim 1 , further comprising 0.0001% to 1.0% of at least one of Sb and Sn. 
     
     
         6 . The steel sheet of  claim 1 , further comprising 0.0001% to 0.01% of B. 
     
     
         7 . The steel sheet of  claim 1 , wherein the steel sheet is one of a hot-rolled steel sheet, a cold-rolled steel sheet, a Zn-based plated steel sheet, and an Al-based plated steel sheet. 
     
     
         8 . The steel sheet of  claim 1 , wherein the steel sheet has a microstructure formed by 30 volume % or more of martensite, bainite, or a combination thereof. 
     
     
         9 . A method of manufacturing a steel sheet for warm press forming, the method comprising:
 heating a steel slab to a temperature within a temperature range of 1000° C. to 1400° C., the steel slab comprising, by weight %, C: 0.01% to 0.5%, Si: 3.0% or less (excluding 0%), Mn: 3% to 15%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, Al: 3.0% or less (excluding 0%), N: 0.03% or less (excluding 0%), and the balance of Fe and inevitable impurities;   forming a hot-rolled steel sheet by performing a hot rolling process on the steel slab and then a finish-rolling process on the steel slab at a temperature within a temperature range of Ar3 to 1000° C.; and   coiling the hot-rolled steel sheet at a temperature higher than Ms but equal to or lower than 800° C.   
     
     
         10 . The method of  claim 9 , further comprising:
 performing a batch annealing process on the hot-rolled steel sheet; and   performing a cold rolling process on the batch-annealed steel sheet to form a cold-rolled steel sheet.   
     
     
         11 . The method of  claim 9 , further comprising plating the steel sheet with a Zn-based material or an Al-based material. 
     
     
         12 . A warm-pressed member comprising, by weight %, C: 0.01% to 0.5%, Si: 3.0% or less (excluding 0%), Mn: 3% to 15%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, Al: 3.0% or less (excluding 0%), N: 0.03% or less (excluding 0%), and the balance of Fe and inevitable impurities,
 wherein after a warm press forming process and a cooling process, the warm-pressed member has a microstructure comprising: 5 volume % to 50 volume % of retained austenite; and at least one of ferrite, martensite, tempered martensite, and bainite as a remainder.   
     
     
         13 . The warm-pressed member of  claim 12 , wherein the warm-pressed member has a tensile strength of 1000 MPa or greater and an elongation of 10% or greater. 
     
     
         14 . A method of manufacturing a member by warm press forming, the method comprising:
 performing a warm press forming process on a steel sheet comprising, by weight %, C: 0.01% to 0.5%, Si: 3.0% or less (excluding 0%), Mn: 3% to 15%, P: 0.0001% to 0.1% S: 0.0001% to 0.03%, Al: 3.0% or less (excluding 0%), N: 0.03% or less (excluding 0%), and the balance of Fe and inevitable impurities; and   cooling the steel sheet,   wherein the warm press forming process comprises a heat treatment process comprising:   heating the steel sheet to a temperature within a temperature range of Ac1 to Ac3 at a heating rate of 1° C./sec to 1000° C./sec; and   maintaining the steel sheet at the temperature within the temperature range for 1 second to 10000 seconds.   
     
     
         15 . The method of  claim 14 , wherein the heat treatment process is performed before the steel sheet is war p eased or after the steel sheet is warm-pressed. 
     
     
         16 . The method of  claim 14 , wherein the cooling is performed at a cooling rate of 1° C./sec to 1000° C./sec. 
     
     
         17 . The method of  claim 10 , further comprising plating the steel sheet with a Zn-based material or an Al-based material. 
     
     
         18 . The method of  claim 15 , wherein the cooling is performed at a cooling rate of 1° C./sec to 1000° C./sec.