Flare workability method of evaluation of forge welding tube

摘要

PROBLEM TO BE SOLVED: To provide a forge-welded pipe which does not cause cracks at a joining part even when subjected to strong working such as flaring by sufficiently improving strength of the joining part of the forge-welded pipe.SOLUTION: The forge-welded pipe is manufactured by heating the whole width in a heating furnace and raising temperature at an edge part of a steel strip with oxidation heat by blowing oxygen or air, or by performing edge-abutting and forge-welding after heating with high frequency. In the forge-welded pipe having good workability, flat height ratio (H) in a flat test in which the joining part 9 of the forge-welded pipe 8 is placed near one end part in the crushing direction is equal to or smaller than a limit flat height ratio (HL2) defined by the formula 1 by using a ratio (R2) of the maximum thickness of a bead part to the pipe thickness. The formula 1: HL2=-6.0×R2+6.56.