High strength hot-rolled steel sheet having excellent hole expansion ratio and manufacturing method for same

Abstract

A high strength hot-rolled steel sheet having an excellent hole expansion ration comprises, by weight %, 0.12% or more and less than 0.30% of carbon (C), 0.1-2.5% of manganese (Mn), 0.5% or less of silicon (Si) (not including 0%), 0.0005-0.005% of boron (B), 0.02% or less of phosphorous (P), 0.01% or less of sulfur (S), and the balance being iron (Fe) and unavoidable impurities, and comprises 95 volume % or more of martensite as a microstructure. And the product of the tensile strength (TS) and hole expansion ratio (HER) can be 30,000 MPa % or greater.

1 . A high strength hot-rolled steel sheet having an excellent hole expansion ratio, comprising:
 by weight %, 0.12% or more and less than 0.30% of carbon (C), 0.1 to 2.5% of manganese (Mn), 0.5% or less of silicon (Si) (not including 0%), 0.0005 to 0.005% of boron (B), 0.02% or less of phosphorous (P), 0.01% or less of sulfur (S), and a balance of iron (Fe) and unavoidable impurities, and 95 volume % or more of martensite as a microstructure,   wherein a product of tensile strength (TS) and hole expansion ratio (HER) is 30,000 MPa % or greater.   
     
     
         2 . The high strength hot-rolled steel sheet having an excellent hole expansion ratio of  claim 1 , wherein the hot-rolled steel sheet further comprises, by weight %, one or more elements of 0.5% or less of chromium (Cr) and 0.005 to 0.2% of titanium (Ti). 
     
     
         3 . The high strength hot-rolled steel sheet having an excellent hole expansion ratio of  claim 1 , wherein the microstructure comprises a total of 5 vol % or less of one or more ferrite, bainite, carbide, and residual austenite. 
     
     
         4 . The high strength hot-rolled steel sheet having an excellent hole expansion ratio of  claim 1 , wherein the hot-rolled steel sheet has tensile strength (TS) of 1,250 MPa or more. 
     
     
         5 . The high strength hot-rolled steel sheet having an excellent hole expansion ratio of  claim 1 , wherein the hot-rolled steel sheet has a hole expansion ratio (HER) of 20% or more. 
     
     
         6 . The high strength hot-rolled steel sheet having an excellent hole expansion ratio of  claim 1 , wherein the hot-rolled steel sheet has a thickness of 1.5 mm or less. 
     
     
         7 . A method of manufacturing a high strength hot-rolled steel sheet having an excellent hole expansion ratio, comprising operations of:
 reheating a slab, including by weight %, 0.12% or more and less than 0.30% of carbon (C), 0.1 to 2.5% of manganese (Mn), 5% or less of silicon (Si) (not including 0%), 0.0005 to 0.005% of boron (B), 0.02% or less of phosphorous (P), 0.01% or less of sulfur (S), and a balance of iron (Fe) and unavoidable impurities;   hot-rolling the reheated slab to provide a hot-rolled steel sheet;   initiating cooling of the hot-rolled steel sheet within 5 seconds of an end point of the hot-rolled steel sheet, and cooling the hot-rolled steel sheet to a cooling end temperature of 350° C. or lower at a cooling rate of 50 to 1,000° C./s; and   winding the cooled hot-rolled steel sheet.   
     
     
         8 . The method of manufacturing a high strength hot-rolled steel sheet having an excellent hole expansion ratio of  claim 7 , wherein the slab further comprises, by weight %, one or more elements of 0.5% or less of chromium (Cr) and 0.005 to 0.2% of titanium (Ti).