| 摘要 |
The present invention provides high strength steel plate with excellent low temperature toughness, high strength steel pipe using this as a base metal, and methods of production of the same. The steel plate of the present invention contains Mo: 0.05 to 1.00% and B: 0.0003 to 0.0100%, has a Ceq of 0.30 to 0.53, has a Pcm of 0.10 to 0.20, and has a metal structure which has an area percentage of polygonal ferrite of 20 to 90% and has a balance of a hard phase comprised of one or both of bainite and martensite. To obtain this steel plate, strain-introducing rolling is performed with a start temperature of not more than Ar 3 +60°C, an end temperature of Ar 3 or more, and a reduction ratio of 1.5 or more, then the plate is air-cooled and then acceleratedly cooled from Ar 3 -100°C to Ar 3 -10°C in temperature by 10°C/s or more. |
