| 摘要 |
<p>This depression-provided steel pipe has plural depressions on an outer peripheral surface, the depressions being formed so as to form a line along an axial direction of the steel pipe, in which each of the depressed portions has, inside thereof, a columnar groove portion extending along the axial direction of the steel pipe and depressed deeper than a bottom surface of these depressed portions; 0.95@HA/HB@1.05 is satisfied, where HA is an average Vickers hardness in each of the depressed portions, and HB is a Vickers hardness at a portion between the depressed portions adjacent to each other in the axial direction of the steel pipe; and the outer peripheral surface is covered with a mill scale.</p> |
