| 摘要 |
PROBLEM TO BE SOLVED: To provide H-type steel excellent in fillet section toughness and its production method. SOLUTION: This H-type steel contains 0.01-0.15% C, 0.60% or lower Si, 0.5-1.8% Mn, 0.030% or lower P, 0.030% or lower S, 0.021-0.05% Al, 0.01-0.10% V, 0.0040-0.0120% N, and 0.001-0.030% Ti, the ratio V/N being 3.6 or higher. The steel after rolling is subjected to forced cooling of which the cooling rate is V/N×3.5 or lower and the cooling stop temperature is in the range of from (Ar<SB>3</SB>-50°C) to (Ar<SB>3</SB>-200°C); thus, a fillet section is imparted with a fine ferrite + pearlite or ferrite + bainite structure with a grain size number (judged according to JIS G 0552) of 5 or higher. COPYRIGHT: (C)2003,JPO
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