| 摘要 |
<p>This steel material satisfies the following conditions: (a) the ZrO 2 content is 5-50%, the REM oxide content is 5-50%, and the CaO content is 50% or less (excluding 0%) when composition of all oxide-based inclusions is measured and then expressed in terms of the mass of the individual oxides; (b) among all the inclusions, those having a circle equivalent diameter of 0.1-2 µm are present in an amount of 120/mm 2 or greater, oxides larger than 3 µm are present in an amount of 5.0/mm 2 or less, and oxides larger than 5µm are present in an amount of 5.0/mm 2 or less; and when the composition of all the inclusions is measured, (c-1) the number of REM- and Zr-containing inclusions I that satisfy the REM/Zr molar ratio of 0.6-1.4 is 30% or greater in relation to the entire number of inclusions, and/or (c-2) the number of REM-, Zr-, Al-, Ca-, and Ti-containing inclusions II is 40% or greater in relation to the entire number of inclusions, inclusions II satisfying the condition in which the ratio of the total number of moles of REM and Zr and the total number of moles of Al, Ca, and Ti is 0.5-1.2. The HAZ toughness is thereby kept at a very high level even when the material is welded with a high heat input of 50 kJ/mm or greater.</p> |
