Patent ID: 9062432
Filing Date: 2015-06-23
Classification: B21C,B21D,E02D

Abstract:
1. A depression-provided steel pipe having 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, wherein 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 <H A /H B <1.05 is satisfied, where H A is an average Vickers hardness in each of the depressed portions, and H B 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.