Steel reinforcement and method for manufacturing the same

Abstract

Provided is a steel reinforcement including an amount of 0.07 to 0.43 wt % of carbon (C), an amount of 0.5 to 2.0 wt % of manganese (Mn), an amount of 0.05 to 0.5 wt % of silicon (Si), an amount greater than 0 and less than or equal to 0.5 wt % of chromium (Cr), an amount greater than 0 and less than or equal to 4.5 wt % of copper (Cu), an amount greater than 0 and less than or equal to 0.003 wt % of boron (B), an amount greater than 0 and less than or equal to 0.25 wt % of vanadium (V), an amount greater than 0 and less than or equal to 0.012 wt % of nitrogen (N), an amount greater than 0 and less than or equal to 0.03 wt % of phosphorus (P), an amount greater than 0 and less than or equal to 0.03 wt % of sulfur(S), an amount of 0.01 to 0.5 wt % of the sum of one or more of nickel (Ni), niobium (Nb) and titanium (Ti), the balance of iron (Fe), and other inevitable impurities. A final microstructure includes ferrite, bainite, pearlite, retained austenite, and precipitates comprising copper.

1 .- 3 . (canceled) 
     
     
         4 . A method for manufacturing a steel reinforcement, the method comprising:
 (a) reheating a steel at a temperature of 1,050 to 1,230° C., wherein the steel comprises an amount of 0.07 to 0.43 wt % of carbon (C), an amount of 0.5 to 2.0 wt % of manganese (Mn), an amount of 0.05 to 0.5 wt % of silicon (Si), an amount greater than 0 and less than or equal to 0.5 wt % of chromium (Cr), an amount greater than 0 and less than or equal to 4.5 wt % of copper (Cu), an amount greater than 0 and less than or equal to 0.003 wt % of boron (B), an amount greater than 0 and less than or equal to 0.25 wt % of vanadium (V), an amount greater than 0 and less than or equal to 0.012 wt % of nitrogen (N), an amount greater than 0 and less than or equal to 0.03 wt % of phosphorus (P), an amount greater than 0 and less than or equal to 0.03 wt % of sulfur(S), an amount of 0.01 to 0.5 wt % of the sum of one or more of nickel (Ni), niobium (Nb) and titanium (Ti), the balance of iron (Fe), and other inevitable impurities;   (b) hot rolling the reheated steel under a condition of a finish rolling temperature of 950 to 1,020° C.; and   (c) performing an aging heat treatment on the hot-rolled steel at a temperature of 400 to 600° C. for 15 to 60 minutes.   
     
     
         5 . The method of  claim 4 , wherein the final microstructure after performing step (c) includes ferrite, bainite, pearlite, retained austenite, and precipitates comprising copper. 
     
     
         6 . The method of  claim 5 , wherein the final microstructure has a bainite fraction of 90% or more and a retained austenite fraction of 5% or less. 
     
     
         7 . The method of  claim 4 , wherein the steel reinforcement after performing the step (c) has a yield strength (YS) of 750 MPa or greater, a tensile strength (TS) of 1,000 MPa or greater, an elongation of 11% or greater, and a ratio of a tensile strength to a yield strength (TS/YS) of 1.25 or greater.