| 摘要 |
A steel sheet or steel pipe being reduced in the expression of the Baushinge r effect, characterized in that it has a dual phase structure consisting substantially of a ferrite structure and a fine martensite phase wherein the fine martensite phase is dispersed in the ferrite structure; and a method fo r producing the steel sheet or steel pipe. The above steel sheet or steel pipe has a chemical composition, in mass %, that C: 0.03 to 0.30 %, Si: 0.01 to 0 .8 %, Mn: 0.3 to 2.5 %, P: 0.03 % or less, S: 0.01 % or less, Al: 0.001 to 0.01 %, N: 0.01 % or less, and the balance: iron and inevitable impurities. The above steel sheet or steel pipe is, in particular, reduced in the decrease o f the compression strength in the perimeter direction being caused by the Baushinger effect when the pipe is expanded, and can be suitably used as a steel pipe for an oil well, a line pipe or the like. |
