HIGH-WORKABILITY STEEL PIPE AND METHOD OF PRODUCING SAME

摘要

The invention provides a steel pipe being superior in workability, particularly in bending workability, in which an r-value in the axial direction of the pipe in a portion where melting or transformation of a steel material has occurred during seam welding is as high as comparable to that in a portion where melting or transformation of the steel material has not occurred, and a method of producing the steel pipe. In the high--workability steel pipe, an r-value in the longitudinal direction is not less than 1.2, more preferably not less than 1.6, over an entire area in the circumferential direction, including a seamed portion. The steel pipe is produced by a method comprising the step of performing diameter-reducing rolling on a steel pipe in a temperature range of from 600.degree.C to Ac3 with a reduction in diameter of not less than 30%, preferably after heating the steel pipe to temperatures of not lower than Ac1, the steel pipe being produced by seam--welding strip steel, or a method further comprising the step of performing heat treatment of holding the rolled steel pipe in a temperature range of from 600.degree.C to 900.degree.C for a time of 1 second or longer during cooling subsequent to the diameter-reducing rolling or by reheating the rolled steel pipe after the cooling.