To provide a method for manufacturing a steel pipe, suitable as magnetic shield, etc., and excellent in the magnetic characteristic.
To the steel pipe having the composition adjusted to ≤0.01% C, ≤1% Mn, ≤0.05% Al, ≤0.005% N and to the suitable ranges of Si. P and S; a shrinkage-diameter rolling, in which the heating temperature is the Ar3 transforming temperature or higher to ≤1,150°C, the rolling-finish temperature is ≥750°C to the Ar3 transforming point or lower and a shrinkage diameter ratio is ≥15%, a cold-drawing work, in which a reducing surface ratio is 3% to <15%, and the annealing treatment, in which the annealing temperature is the Ac1 transforming point or higher to lower than the Ac3 transforming point, are applied in order. By this method, the steel pipe having the structure of ≥500 μm the average crystal grain diameter and ≥3.0 the X-ray three-dimension random intensity ratio in the crystal orientation of the <100> direction in the pipe circular direction and <110> direction in the pipe axial direction, and excellent in the magnetic characteristic, can be obtained.
KAWABATA YOSHIKAZU
ISHIGURO YASUHIDE
MATSUOKA SAIJI
ITAYA MOTOAKI
