| 摘要 |
PROBLEM TO BE SOLVED: To develop a high tensile strength steel improved in low temp. toughness in the HAZ and excellent in plating cracking resistance by finely dispersing multi-oxides having a cubic system M3 O4 type crystal structure and essentially consisting of Al, Mn and Ti into the steel structure. SOLUTION: In a steel having a compsn. contg., by weight, 0.05 to 0.20% C, <0.50% Si, 0.20 to 2.0% Mn, <0.030% P, <0.030% S, <0.020% Al, <0.050% Ti, 0.001 to 0.010% O and <0.010% N, grains contg. cubic system M3 O4 type multi-oxide phases having 1 to 10μm diameter and contg., by atom, 5 to 50% Mn and 50 to 95% Al+Ti are dispersed into the structure by 4 pieces per mm<2> , by which the high tensile strength steel having >=500MPa tensile strength, having HAZ toughness of >=100J Charpy impact value at -30 deg.C and having excellent plating cracking resistance can be produced.
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