SEAMLESS STEEL PIPE, HOLLOW SPRING UTILIZING SEAMLESS STEEL PIPE, AND PROCESS FOR MANUFACTURING THE SAME
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United States of America Patent
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Issued Date -
Feb 18, 2010
app pub date -
Mar 14, 2007
filing date -
Mar 14, 2007
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Abstract
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.
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