Offshore structural steel having a good low-temperature toughness for high heat input welding

摘要

Provided is a high heat input steel material with excellent low-temperature toughness for an offshore structure. According to the present invention, the steel material for the offshore structure comprises: 0.070 weight percent or less of carbon (C); 0.05 to 0.30 weight percent or less of silicon (Si); 1.4 to 2.2 weight percent or less of manganese (Mn); 0.024 weight percent or less of solid solution-aluminum (sol-Al); 0.20 weight percent or less of copper (Cu); 0.4 to 2.5 weight percent of nickel (Ni); 0.001 weight percent or less of niobium (Nb); 0.005 to 0.015 weight percent of titanium (Ti); 0.002 to 0.005 weight percent of nitrogen (N); and the remainder of Fe and inevitable impurities. Moreover, the steel material for the offshore structure has a yield strength of 350 MPa or higher at a welding heat input amount of 5 to 15.0 kJ/mm, has excellent low temperature impact toughness and has a crack tip opening displacement (CTOD) of 0.25 mm or more at -10°C.