Die, method of manufacturing stepped metal pipe or tube, and stepped metal pipe or tube

摘要

A die through hole has an inside surface including a bell portion, an approach portion, and a bearing portion from the entrance side. The diameter of the approach portion is D 1 on its entrance side and D 2 on its exit side and gradually decreases from the entrance side to the exit side. The diameter satisfies Equation (1): 0.7<=D 2 /D 1 <0.97. The die half angle of an inside surface where the diameter D 3 is D 2 /0.97 is not less than the die half angle R 2 of an inside surface nearer to the approach portion exit side than the inside surface where the diameter is D 3 . The axial distance LR from the inside surface where the diameter is D 3 to the inside surface where the diameter is D 2 satisfies Equation (2): 20<=LR/((D 3 -D 2 )/2)<=115. The through hole diameter at the bearing portion is fixed at D 2 , and the length is LB and satisfies Equation (3): 0.3<=LB/D 2 <=10.