| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength steel excellent in toughness in the extra-large heat input weld heat-affected zone with >=200 kJ/cm (e.g. even in the case of about 1,500 kJ/cm) heat input. SOLUTION: With MgAl2 O4 of 0.005 to 0.1μm particle size as the nuclei, and in the vicinity thereof, MgAl2 O4 -TiN blended particles of 0.05 to 2.0μm size contg. TiN are contained. The steel has a compsn. contg., by weight, 0.04 to 0.2% C, 0.02 to 0.5% Si, 0.6 to 2.0% Mn, <=0.02% P, <=0.02% S, 0.003 to 0.01% Al, 0.005 to 0.025% Ti, 0.002 to 0.008% N, 0.0002 to 0.005% Mg and 0.0005 to 0.008% O, contg. suitable quantity of one or >= two kinds among Cu, Ni, Cr, Mo, Nb, V and B as selective elements, and the balance Fe with inevitable impurities. By the suppress of the growth ofγparticles in the extra- large heat input weld heat-affected zone, its toughness can be improved.
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