PLUG FOR COLD DRAWING AND PRODUCTION METHOD OF METAL PIPE

摘要

A plug (1) has a first columnar portion (20), a tapered portion (30), and a second columnar portion (40). The first columnar portion (20) has an outside diameter D1. The second columnar portion (40) has an outside diameter D2 larger than D1. The tapered portion (30) is formed between the first columnar portion (20) and the second columnar portion (40). The tapered portion (30) has a tapered surface (31) the outside diameter of which increases gradually from the first columnar portion (20) toward the second columnar portion (40), and an axial length L. The outside diameters D1 and D2 of the plug (1), and the axial length L satisfy the expressions (1) through (4). The cold drawing plug can therefore reduce residual tensile stress on the outer surface of a metal pipe after cold drawing. 0.25=?=2.00 (1), 0.06=L/D2=0.8 (2), L/D2=0.3x?+0.575 (3), L/D2=0.1x? (4), where, ?=(D2-D1)/D1x100.