| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel material superior in the toughness of a weld heat-affected zone, and to provide a manufacturing method therefor. SOLUTION: The steel material superior in the toughness of the weld heat-affected zone comprises 0.01-0.2% C (which means mass%, and hereafter the same), 0.05-0.5% Si, 0.5-2.5% Mn, 0.005-0.06% Ti and 0.002-0.01% N; 0.02% or less P (including 0%), 0.008% or less S (including 0%) and 0.01% or less Al (including 0%), which are inhibited elements; further 0.001-0.1% La and/or Ce in total; and the balance Fe with unavoidable impurities. Furthermore, in the steel material, the total mass of La<SB>2</SB>O<SB>3</SB>and Ce<SB>2</SB>O<SB>3</SB>occupies 55% or more in the average composition of oxide-based inclusions contained in the steel material, and a ratio of the total mass of La<SB>2</SB>O<SB>3</SB>and Ce<SB>2</SB>O<SB>3</SB>to the mass of SiO<SB>2</SB>in the above average composition, [(La<SB>2</SB>O<SB>3</SB>+Ce<SB>2</SB>O<SB>3</SB>)/SiO<SB>2</SB>], occupies 5.0 to 105. COPYRIGHT: (C)2005,JPO&NCIPI
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