| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a structural steel having excellent resistance to propagating fatigue crack even under repeated loads so as prolong the life of a structure and secure structural safety. SOLUTION: A steel bloom, which has a composition consisting of 0.02-0.25% C, 0.03-0.6% Si, 0.3-2.0% Mn, 0.01-0.1% Al, 0.01-0.1% Nb, 0.01-0.1% Ti and the balance Fe with impurities and satisfying (0.7+C)/ (Si/25)+(Mn/5)+(Nb/25)+ Ti}<=4.0, is heated to >=1,050 deg.C, hot rolled at 1,040-740 deg.C rolling finishing temperature, and then cooled from a temperature between (Ts1+500) and (Ts1-25) deg.C down to at least 550 deg.C at (5 to 50) deg.C/s cooling rate. Moreover, Ts1=(820-200 C-60Si-600Nb+2000Ti) is satisfied; and the symbol of elements in respective inequality and equation represents the content of the element itself.
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