| 摘要 |
The present invention provides a line pipe of, e.g., the API standard X60 to X100 class. The line pipe has an excellent deformability, as well as excellent low temperature toughness and high productivity, a steel plate used as the material of the steel pipe. Methods for producing the steel pipe and the steel plate are also provided. In particular, a high-strength steel plate excellent in the deformability has a ferrite phase is dispersed finely, and accounts for 5% to 40% in area percentage in a low temperature transformation structure mainly composed of a bainite phase. For example, most grain sizes of the ferrite phase are smaller than the average grain size of the bainite phase. A high-strength steel pipe excellent in deformability is also provided, in which a large diameter steel pipe is produced through forming the steel plate into a pipe shape. The steel pipe has the above-referenced structure, and satisfies the conditions that YS/TS is 0.95 or less and YS×uEL is 5,000 or more. Methods for producing such steel plate and steel pipe are also provided. |
