| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel in which variation in HAZ toughness is reduced, and further, the low temperature toughness of the base metal itself is increased as well, and to provide a method for producing the same. SOLUTION: The invention is characterized in that: (A) the steel comprises inclusions including REM and Zr; (B) solid solution REM and solid solution Zr in the steel satisfy solid solution REM:≤0.0010% (including 0%) and solid solution Zr:≤0.0010% (including 0%); and (C), when the metallic structure of the steel is observed by an EBSP (Electron Diffraction Image) method, the steel satisfies inequality; D≤30 (wherein, D denotes the average equivalent circle diameter (μm) of the crystal grains surrounded by large angle boundaries with a crystal orientation difference of≥15°upon measurement of the orientation difference of the adjoining two crystals by an EBSP method), and inequality; 50≤M (wherein, M denotes the ratio (area%) of the crystal grains surrounded by large angle boundaries with a crystal orientation difference of≥55°occupied in the whole of the steel). COPYRIGHT: (C)2010,JPO&INPIT
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