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

摘要

This invention provides a high-strength steel, which has unprecedentedly excellent CTOD (fracture toughness) properties, that is, for example, in multilayer welding of small to middle heat input, can satisfy, in addition to CTOD properties in an FL part at -60°C, CTOD properties in an IC part, and a process for producing the steel. The steel has a weld heat-affected zone having excellent CTOD properties and is characterized by comprising, 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: not more than 0.008%, S: not more than 0.005%, Al: not more than 0.004%, Ti: 0.005 to 0.015%, Nb: not more than 0.005%, O: 0.0015 to 0.0035%, and N: 0.002 to 0.006% with the balance consisting of iron and unavoidable impurities, the steel having a PCTOD value of not more than 0.065 and a CeqH value of not more than 0.235.