STEEL WITH WELD HEAT-AFFECTED ZONE HAVING EXCELLENT CTOD PROPERTIES AND PROCESS FOR PRODUCING THE STEEL

摘要

The present invention provides high strength steel having unprecedentedly superior CTOD (fracture toughness) properties satisfying not only the CTOD properties of the FL zone at -60°C, but also the CTOD properties of the ICHAZ zone in small and medium heat input multilayer welding etc. and a method of production of the same.;The steel of the present invention is steel superior in CTOD properties of the heat-affected zone containing, by mass%, C: 0.015 to 0.045%, Si: 0.05 to 0.2%, Mn: 1.5 to 2.0%, Cu: 0.25 to 0.5%, Ni: 0.7 to 1.5%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, Nb: 0.005% or less, O: 0.0015 to 0.0035%, and N: 0.002 to 0.006%, PCTOD: 0.065 or less, CeqH: 0.235 or less and the balance consisting of Fe and unavoidable impurities.