| 摘要 |
PROBLEM TO BE SOLVED: To provide an extra thick wide flange shape having the high strength and excellent in Z-directional toughness in the center of thickness of a flange part. SOLUTION: This extra thick wide flange shape excellent in toughness in the center of thickness of a flange part and having >=325 MPa yield strength has a composition which consists of 0.05-0.18% C, <=0.60% Si, 1.00-1.80% Mn, <=0.020% P, <0.004% S, 0.016-0.050% Al, 0.04-0.15% V. 0.0070-0.0200% N, one or >=2 kinds among 0.02-0.60% Cu, 0.02-0.60% Ni, 0.02-0.50% Cr, and 0.01-0.20% Mo, Ti in an amount in the range satisfying 0.002<=Ti<=1.38×N-8.59×10<-4> , and the balance Fe with inevitable impurities and in which Ceq, represented by Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V/14, is regulated to 0.36 to 0.45% and V×N/s>=0.150 is satisfied. Changes in Z-directional Charpy absorption energy and ferrite grain size, in the case where the value of V×N/S is changed by changing the additive quantity of V or N by fixing the amount of S, are shown. |
