Process for manufacturing seamless steel pipe, hollow spring utilizing seamless steel pipe

Patent metadata

Field	Value
Publication number	US-9482302-B2
Application number	US-201313892009-A
Country	US
Kind code	B2
Filing date	May 10, 2013
Priority date	Mar 14, 2007
Publication date	Nov 1, 2016
Grant date	Nov 1, 2016

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.

First claim

The invention claimed is:

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 performed at 1,050° C. or more and less than 1,300° C. to obtain a seamless steel pipe workpiece;
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; wherein
a second heating step is not performed between the hot isostatic extrusion step and the extension step.

2. The method according to claim 1 , further comprising a straightening step in which bend of the pickled seamless steel pipe is straightened, after the pickling step.

3. The method according to claim 1 , further comprising a grinding step in which an inner periphery surface of the heated seamless steel pipe workpiece is ground.

4. The method according to claim 2 , wherein an inner periphery surface of the seamless steel pipe is ground after the straightening step.

5. The method according to claim 1 , wherein the first heating step includes heating the billet at 1,050° C. or more and less than 1,300° C.

6. The method according to claim 1 , wherein the extension step, the third heating step, and the pickling step are repeated a predetermined number of times.

7. The method according to claim 1 , wherein the hot isostatic extrusion processing performed at 1,100° C. or more and less than 1,200° C.

8. The method according to claim 1 , wherein the extension step includes:
extending the seamless steel pipe workpiece by drawing processing; and thereafter,
stretching the seamless steel pipe workpiece using a die through the Pilger mill rolling.

9. The method according to claim 1 , wherein the extension step includes extending the seamless steel pipe workpiece 25% or less in one pass.

10. The method according to claim 1 , wherein the third heating step includes heating the seamless steel pipe workpiece to 650 to 750° C.

11. 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 performed at 1,050° C. or more and less than 1,300° C. to obtain a seamless steel pipe workpiece;
a slow-cooling step in which the seamless steel pipe workpiece that has been subjected to the hot isostatic extrusion processing is slowly cooled at a rate of 0.1° C./sec or more and less than 0.3° C./sec;
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; wherein
a second heating step is not performed between the hot isostatic extrusion step and the extension step.

12. The method according to claim 11 , wherein the hot isostatic extrusion step includes placing the heated billet into a container and pressing the heated billet by a sealing piston through a pressure medium.

13. The method according to claim 12 , wherein the pressure medium comprises a viscoplastic pressure medium.

Assignees

• Shinko Metal Prod
• Nhk Spring Co Ltd

Inventors

• Toyotake Kotaro
• Iwaya Koji
• Minami Tomoyuki
• Takamura Noritoshi

Classifications

• B21C23/085

  Making tubes (B21C23/10 take precedence) · CPC title

• C22C38/46

  with vanadium · CPC title

• C21D9/08

  for tubular bodies or pipes · CPC title

• B21F3/02

  helically · CPC title

• B21B19/04 Primary

  Rolling basic material of solid, i.e. non-hollow, structure; Piercing {, e.g. rotary piercing mills} · CPC title