PROCESS FOR MANUFACTURING SEAMLESS STEEL PIPE, HOLLOW SPRING UTILIZING SEAMLESS STEEL PIPE

摘要

There are provided: a seamless steel pipe formed from a cylindrical steel material billet through a hot isostatic extrusion step, wherein a depth of a contiguous flaw formed on an inner periphery surface and an outer periphery surface of the steel pipe is 50 μm or less; a hollow spring obtained by forming a hollow body in a shape of a coil or a bar or a bar with curved part from the seamless steel pipe made of spring steel and applying a surface treatment to the hollow body so that the hollow body has compressive residual stress; and a method for producing seamless steel pipe including: a billet molding step; a first heating step; a hot isostatic extrusion step; a second heating step; an extension step; a third heating step; and a pickling step.

主权项

1. A method for producing seamless steel pipe comprising:
a billet molding step in which a steel material is molded into a cylindrical billet; a first heating step in which the billet is heated; a hot isostatic extrusion step in which the heated billet is subjected to hot isostatic extrusion processing to obtain a seamless steel pipe workpiece; a second heating step in which the seamless steel pipe workpiece is heated; an extension step in which the heated seamless steel pipe workpiece is extended by at least one of Pilger mill rolling and drawing processing; a third heating step in which the extended seamless steel pipe workpiece is heated; and a pickling step in which the extended and heated seamless steel pipe workpiece is pickled.