| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a steel material for structural use excellent in earthquake-proof characteristic having excellent breaking toughness under high speed deformation without adding much contents of precious alloy elements. SOLUTION: A steel blank containing, by wt%, 0.04-0.15% V and 0.0050-0.0150% N, is heated and hot-rolling is applied at the finish temperature of the rolling not lower than Ar<SB>3</SB>transforming point. Thereafter, this hot-rolled steel is cooled at 0.09-1°C/s cooling speed and VN deposit is precipitated at 0.02-0.07% and fine ferrite + pearlite structure having≥50% ferritic area ratio is made in the micro-structure. Further, in the ferrite grain, 10<SP>6</SP>- 10<SP>10</SP>pieces/mm<SP>3</SP>of the VN deposits having 5 - 200 nm grain diameter, are precipitated and dispersed. In this way, the deformation at the tip part of crack, is uniformed and even in the case of being the absorbing energy value in a Charpy impact test as the same, the steel material having high breaking toughness (≥0.1 mm the limit CTOD value at 0°C) at the deforming time in the high speed, is obtained. COPYRIGHT: (C)2004,JPO&NCIPI
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