High strength steel plate for structure with good seawater corrosion resistant property and method of manufacturing same

Abstract

The present invention provides a high strength steel plate for a structure and a method of manufacturing same, wherein the high strength steel plate fora structure comprises, by weight %, 0.03% (inclusive) to 0.1% (exclusive) of C, 0.1% (inclusive) to 0.8% (exclusive) of Si, 0.3% (inclusive) to 1.5% (exclusive) of Mn, 0.5% (inclusive) to 1.5% (exclusive) of Cr, 0.1% (inclusive) to 0.5% (exclusive) of Cu, 0.01% (inclusive) to 0.08% (exclusive) of Al, 0.01% (inclusive) to 0.1% (exclusive) of Ti, 0.05% (inclusive) to 0.1% (exclusive) of Ni, 0.002% (inclusive) to 0.07% (exclusive) of Nb, 0.03% or less of P, 0.02% or less of S, and the balance of Fe and unavoidable impurities, and has a microstructure comprising, by area fraction, 20% or more of bainite, less than 80% of polygonal ferrite and acicular ferrite in total, and less than 10% of pearlite and MA as the other phases.

1 . A high-strength steel for a structure comprising, by weight, carbon (C): 0.03% or more to less than 0.1%, silicon (Si): 0.1% or more to less than 0.8%, manganese (Mn): 0.3% or more to less than 1.5%, chromium (Cr): 0.5% or more to less than 1.5%, copper (Cu): 0.1% or more to less than 0.5%, aluminum (Al): 0.01% or more to less than 0.08%, titanium (Ti): 0.01% or more to 0.1% or less, nickel (Ni): 0.05% or more to less than 0.1%, niobium (Nb): 0.002% or more to less than 0.07%, phosphorus (P): 0.03% or less, sulfur (S): 0.02% or less, and a balance of iron (Fe) and unavoidable impurities,
 wherein the high-strength steel has a microstructure comprising, by area fraction, 20% or more of bainite, less than 80% of polygonal ferrite and acicular ferrite in total, and less than 10% of pearlite and MA as the other phases.   
     
     
         2 . The high-strength steel for a structure of  claim 1 , wherein the carbon (C) is contained in an amount of 0.03% or more to less than 0.09%. 
     
     
         3 . The high-strength steel for a structure of  claim 1 , wherein the silicon (Si) is contained in an amount of 0.2% or more to less than 0.8%. 
     
     
         4 . The high-strength steel for a structure of  claim 1 , wherein the copper (Cu) is contained in an amount of 0.1% or more to less than 0.45%. 
     
     
         5 . The high-strength steel for a structure of  claim 1 , which has yield strength of 500 MPa and tensile strength of 600 MPa. 
     
     
         6 . A method of manufacturing a high-strength steel for a structure, the method comprising:
 reheating a slab to a temperature of 1000° C. or more to 1200° C. or less, the slab comprising, by weight, carbon (C): 0.03% or more to less than 0.1%, silicon (Si): 0.1% or more to less than 0.8%, manganese (Mn): 0.3% or more to less than 1.5%, chromium (Cr): 0.5% or more to less than 1.5%, copper (Cu): 0.1% or more to less than 0.5%, aluminum (Al): 0.01% or more to less than 0.08%, titanium (Ti): 0.01% or more to 0.1% or less, nickel (Ni): 0.05% or more to less than 0.1%, niobium (Nb): 0.002% or more to less than 0.07%, phosphorus (P): 0.03% or less, sulfur (S): 0.02% or less, and a balance of iron (Fe) and unavoidable impurities;   hot rolling the reheated slab within a finish rolling temperature of 750° C. or more to 950° C. or less; and   cooling a rolled steel plate from a cooling initiation temperature of 750° C. or more to a cooling finish temperature of 400° C. to 700° C. at a cooling rate of 10° C./sec or more.