| 摘要 |
PROBLEM TO BE SOLVED: To provide a wide flange shape for steel arch timbering having high strength of >=590 MPa tensile strength, also small in the secular deterioration in mechanical properties after cold working and excellent in weather resistance. SOLUTION: This wide flange shape has a compsn. contg., by weight, 0.14 to 0.18% C, 0.25 to 1.0% Si, 1.0 to 1.8% Mn, 0.35 to 0.60% Cu, <=0.05% Al, <=0.035% P, <=0.020% S, <=0.0050% N and <=0.00025% H, moreover contg. one or >= two kinds selected from the group of 0.01 to 0.2% V, 0.005 to 0.10% Nb and 0.002 to 0.10% Ti, and the balance substantially Fe with inevitable impurities, and in which carbon equivalent (Ceq) defined by the formula of Ceq=[%C]+[%Mn]/6+[%Si]/24+[%Cr]/5+[%Mo]/4+[%Ni]/40+[%V]/14 is <=0.47.
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