The steel and its production mannered null mass which for welding structure are superior in Characteristic of the welding

摘要

PROBLEM TO BE SOLVED: To provide steel in which toughness in weld heat-affected zone exhibits a stably high value and also to provide a method for manufacturing the steel.;SOLUTION: The steel for welded structure has a composition consisting of, by mass, 0.01 to 0.2% C, 0.03 to 0.5% Si, 0.5 to 2.0% Mn, ≤0.02% P, ≤0.01% S, 0.005 to 0.08% Al, 0.0005 to 0.02% Ti, 0.0003 to 0.02% Ca, 0.001 to 0.009% N, 0.0010 to 0.0025% O (oxygen) and the balance Fe with impurities and satisfying inequality 0.50≤Ca/O≤1.30 and also has a structure in which 1×10 to 1×10⁴ pieces/mm² of CaO-Al₂O₃ inclusions of 0.5 to 5μm grain size are dispersed. The steel can be manufactured by adding Al so that Al in molten steel becomes 0.005 to 0.08% to perform deoxidation, adding Ti, further treating the molten steel in a degassing apparatus for ≥15 min, adding Ca in a state where the temperature of the molten steel is held at 1,600±70°C and then carrying out casting and rolling.;COPYRIGHT: (C)2007,JPO&INPIT