| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high tensile steel excellent in low-temperature toughness and crack arrest properties, the high tensile steel being excellent in crack arrest properties as well as in strength and toughness. SOLUTION: A steel blank containing specified contents of C, Si, Mn, P, S, Ni, Ti and N satisfying Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B≤0.25% and the balance Fe with inevitable impurities, is heated to 1,000-1,200°C, and the hot-rolling in≥8% cumulative rolling-reduction ratio at Ac<SB>3</SB>point+20°C to Ar<SB>3</SB>point+100°C is applied to the heated steel blank, then an accelerated cooling starting from Ar<SB>3</SB>point-30°C to Ar<SB>3</SB>point+80°C and completing at≤500°C, is applied to the hot-rolled steel at 5 to 100°C/sec cooling speed, and the thickness of priorγgrain on the surface layer, is controlled to≤12μm, and the crystal having≤5μm diameter on the surface layer after transforming, is present at an area ratio of 10% or more. COPYRIGHT: (C)2009,JPO&INPIT
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