| 摘要 |
The present invention provides a steel pipe having a low yield ratio and is: a steel pipe having a low yield ratio, wherein the steel pipe contains, in mass, 0.01 to 0.20% C, 0.05 to 1.0% Si, 0.1 to 2.0% Mn and 0.001 to 0.05% Al, the microstructure of the steel pipe is composed of ferrite and pearlite, or ferrite and cementite, and the average size of the ferrite grains is not smaller than 20 mu m; and a steel pipe having a low yield ratio, wherein the steel pipe contains, in mass, 0.03 to 0.20% C, 0.05 to 1.0% Si, 0.1 to 2.0% Mn, 0.001 to 0.05% Al, 0.01 to 0.5% Nb and 0.001 to 0.01% N, the microstructure of the steel pipe is composed of ferrite and bainite, or ferrite, martensite and bainite, or ferrite and martensite, and the average size of the ferrite grains is not smaller than 20 mu m.
|
