| 摘要 |
PROBLEM TO BE SOLVED: To provide an earthquake-proof steel tube hardly causing local buckling at the time of big earthquake. SOLUTION: This steel tube is an earthquake-proof welded steel tube produced by using a hot rolled steel plate as a material and has a chemical composition which contains, by weight, 0.03-0.15% C, 1.0-2.0% Mn, and one or more kinds among 0.05-0.50% Cu, 0.05-0.50% Ni, 0.05-0.50% Cr, 0.05-0.50% Mo, 0.005-0.10% Nb, 0.005-0.10% V, and 0.005-0.080% Ti and in which the value of PCM, represented by equation PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+ Mo/15+V/10+5×B (where the symbol of element stands for the weight percentage of each element), is regulated to 0.10-0.25. Further, the work hardening index at the tensile test in a tube-axis direction is >=0.10.
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