Seamless steel pipe for hollow spring

Patent metadata

Field	Value
Publication number	US-9650704-B2
Application number	US-201314407106-A
Country	US
Kind code	B2
Filing date	Jun 11, 2013
Priority date	Jun 11, 2012
Publication date	May 16, 2017
Grant date	May 16, 2017

Abstract

A seamless steel pipe for a hollow spring includes C: 0.2 to 0.7 mass %, Si: 0.5 to 3 mass %, Mn: 0.1 to 2 mass %, Cr: 3 mass % or less (excluding 0 mass %), Al: 0.1 mass % or less (excluding 0 mass %), P: 0.02 mass % or less (excluding 0 mass %), S: 0.02 mass % or less (excluding 0 mass %) and N: 0.02 mass % or less (excluding 0 mass %). A residual austenite content in an inner surface layer part of the steel pipe is 5 vol. % or less. An average grain size of a ferrite-pearlite structure in the inner surface layer part of the steel pipe is 18 μm or less. A number density of a carbide having a circle equivalent diameter of 500 nm or more and being present in the inner surface layer part of the steel pipe is 1.8×10 −2 particles/μm 2 or less.

First claim

The invention claimed is:

1. A seamless steel pipe for a hollow spring, comprising iron, 0.2 mass % to 0.7 mass % of C, 0.5 mass % to 3 mass % of Si, 0.1 mass % to 2 mass % of Mn, more than 0 mass % and 3 mass % or less of Cr, more than 0 mass % and 0.1 mass % or less of Al, more than 0 mass % and 0.02 mass % or less of P, more than 0 mass % and 0.02 mass % or less of S and more than 0 mass % and 0.02 mass % or less of N, wherein a residual austenite content in an inner surface layer part of the steel pipe is 5 vol. % or less, an average grain size of a ferrite-pearlite structure in the inner surface layer part of the steel pipe is 18 μm or less and a number density of a carbide which has a circle equivalent diameter of 500 nm or more and is present in the inner surface layer part of the steel pipe is 1.8×10 −2 particles/μm 2 or less.

2. The seamless steel pipe for a hollow spring according to claim 1 , further comprising more than 0 mass % and 0.015 mass % or less of B.

3. The seamless steel pipe for a hollow spring according to claim 2 , further comprising at least one selected from the group consisting of more than 0 mass % and 1 mass % or less of V, more than 0 mass % and 0.3 mass % or less of Ti and more than 0 mass % and 0.3 mass % or less of Nb.

4. The seamless steel pipe for a hollow spring according to claim 3 , further comprising at least one selected from the group consisting of more than 0 mass % and 3 mass % or less of Ni and more than 0 mass % and 3 mass % or less of Cu.

5. The seamless steel pipe for a hollow spring according to claim 1 , further comprising at least one selected from the group consisting of more than 0 mass % and 1 mass % or less of V, more than 0 mass % and 0.3 mass % or less of Ti and more than 0 mass % and 0.3 mass % or less of Nb.

6. The seamless steel pipe for a hollow spring according to claim 5 , further comprising at least one selected from the group consisting of more than 0 mass % and 3 mass % or less of Ni and more than 0 mass % and 3 mass % or less of Cu.

7. The seamless steel pipe for a hollow spring according to claim 1 , further comprising more than 0 mass % and 2 mass % or less of Mo.

8. The seamless steel pipe for a hollow spring according to claim 1 , further comprising at least one selected from the group consisting of more than 0 mass % and 0.005 mass % or less of Ca, more than 0 mass % and 0.005 mass % or less of Mg and more than 0 mass % and 0.02 mass % or less of REM.

9. The seamless steel pipe for a hollow spring according to claim 1 , further comprising at least one selected from the group consisting of more than 0 mass % and 0.1 mass % or less of Zr, more than 0 mass % and 0.1 mass % or less of Ta and more than 0 mass % and 0.1 mass % or less of Hf.

Assignees

• Kobe Steel Ltd
• Shinko Metal Prod
• Kobe Steel Ltd

Inventors

• Kochi Takuya
• Hatano Hitoshi
• Tamura Eiichi
• Toyotake Kotaro

Classifications

• Y10T428/12292

  Workpiece with longitudinal passageway or stopweld material [e.g., for tubular stock, etc.] · CPC title

• C22C38/54 Primary

  with boron · CPC title

• C22C38/34

  with more than 1.5% by weight of silicon · CPC title

• C22C38/28

  with titanium or zirconium · CPC title

• C22C38/26

  with niobium or tantalum · CPC title