| 摘要 |
PROBLEM TO BE SOLVED: To provide a heat treated high tensile strength steel, having a strength level regulated to 70-80kgf class by means of tempering and also having excellent weldability and resistance to hot dip galvanizing crack, and its production. SOLUTION: The heat treated high tensile strength steel, excellent in weldability and resistance to hot dip galvanizing crack, has a composition which contains, by weight, 0.06-0.12% C, 0.1-0.25% Si, 0.8-1.6% Mn, 0.008-0.05% Nb, 0.02-0.1% V, 0.008-0.015% Ti, (0.0005+Ti/3.4) to 0.01% N, and <0.00016% B and in which the value of Pcm, represented by Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B, is regulated to <=0.21% and also the value of Z=Ceq+600×B, defined by Ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+ V/14 and B content, is regulated to <=0.40.
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