| 摘要 |
PROBLEM TO BE SOLVED: To obtain a steel with low yield point, excellent in toughness and used for an energy absorption device for building at the time of earthquake, by limiting the relationship among respective quantities of C, Ti, and N, reducing the amount of effective C, and limiting a microstructure to a proper range. SOLUTION: The steel has a compositon which consists of, by weight, <=0.1% C, <=0.4% Si, $1.5% Mn, <=0.025% P, <=0.015% S, <=0.06% Al, 0.005-0.4% Ti, <=0.006% N, and the balance iron with inevitable impurities and in which the relationship among respective quantities of C, Ti, and N, expressed in weight percentage, satisfies -0.02%<=C-(Ti-3.4N)/4<=0.01%. Further, the steel has a ferritic structure of >=95% microstructure and has a crystalline grain size of >=20μm by circle equivalent diameter, and the ductile/brittle fracture transition temperature (vTrs) at the V Charpy impact test is regulated to <=0 deg.C.
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