| 摘要 |
PROBLEM TO BE SOLVED: To provide a relatively inexpensive earthquake-proof structural steel having excellent toughness even after subjected to repeated prestrain due to earthquake load and suitable for use in the fields of construction and civil engineering, etc., and a method of manufacturing the structural steel relatively easily. SOLUTION: The structural steel excellent in earthquake resistance has a chemical composition which consists of 0.02-0.15% C, 0.2-0.7% Si, 0.8-2.0% Mn, 0.05-0.80% Cr, 0.01-0.08% Nb, 0.005-0.040% Ti, 0.01-0.10% Al, and the balance Fe with inevitable impurities and in which the contents of P and S among the impurities are regulated to <=0.02% and <=0.02%, respectively. Further, the structure of this steel is composed of ferrite/bainite two-phase structure, and the hardness and proportion of the bainitic phase are regulated to >=220 Vickers hardness and 55-95%, respectively.
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