| 摘要 |
PROBLEM TO BE SOLVED: To provide steel having excellent toughness in heat affected zone(HAZ) even at high heat input welding where the amount of heat input exceeds 20 kJ/mm. SOLUTION: This steel for extremely high heat input welding, excellent in toughness in HAZ, has a composition containing, by mass, 0.02-0.2% C, 0.02-0.5% Si and 0.3-2.0% Mn, containing respectively controlled amounts of P, S, Al, Ti, Mo and O, also containing, by mass, one or more kinds among 0.05-1.0% Zr, 0.002-0.02% La and 0.002-0.02% Ce, and having the balance iron with inevitable impurities. Further, the steel contains (1.0×105 to 1.0×108) pieces/mm2 of nitride/oxide composite particles with a size of 0.01-2.0μm constituted of nitrides in which MgO or Mg-containing oxides of 0.005-0.5μm particle size are used as nuclei and the oxides are contained or deposited in the periphery.
|
