Steel having excellent low-temperature fracture toughness and method of manufacturing the same

摘要

The present invention provides a steel material having excellent low-temperature fracture toughness by increasing toughness by performing a tempering treatment after a cooling step after normalizing treatment. According to an embodiment of the present invention, the steel material is by weight, carbon (C): 0.13% to 0.17%, silicon (Si): 0.15% to 0.40%, manganese (Mn): 1.00% to 1.30%, phosphorus (P): >0% to 0.012%, Sulfur (S): >0% to 0.003%, Soluble Aluminum (S_Al): 0.015% to 0.05%, Chromium (Cr): >0% to 0.25%, Nickel (Ni) ): 0.15% to 0.25%, Titanium (Ti): >0% to 0.01%, Copper (Cu): 0.10% to 0.20%, Niobium (Nb): 0.01% to 0.02%, Molybdenum (Mo): >0% ~ 0.08%, vanadium (V): more than 0% ~ 0.010%, and the balance contains iron (Fe) and unavoidable impurities, tensile strength (TS): 500 MPa to 550 MPa, yield strength (YS): 300 MPa ~ 350 MPa, elongation (EL): 30% ~ 40%, and Charpy impact absorption energy: satisfies 300 J ~ 400 J at a temperature of 0 ℃ ~ -60 ℃, and has a needle-like structure.