High cleanliness spring steel and high cleanliness spring excellent in fatigue properties

Patent metadata

Field	Value
Publication number	US-9441695-B2
Application number	US-201514593581-A
Country	US
Kind code	B2
Filing date	Jan 9, 2015
Priority date	Jun 9, 2006
Publication date	Sep 13, 2016
Grant date	Sep 13, 2016

Abstract

High cleanliness spring steel useful in manufacturing a spring with SiO 2 -based inclusions being extremely controlled and excellent in fatigue properties is provided.
High cleanliness spring steel which is steel containing;
C: 1.2% (means mass %, hereafter the same with respect to the component) or below (not inclusive of 0%), Si: 1.2-4%, Mn: 0.1-2.0%, Al: 0.01% or below (not inclusive of 0%),

and the balance comprising iron with inevitable impurities, wherein;

the total of oxide-based inclusions of 4 or above of L (the large diameter of an inclusion)/D (the short diameter of an inclusion) and 25 μm or above of D and oxide-based inclusions of less than 4 L/D and 25 μm or above of L, in the oxide-based inclusions of 25 mass % or above of oxygen concentration and 70% (means mass %, hereafter the same with respect to inclusions) or above of SiO 2 content when Al 2 O 3 +MgO+CaO+SiO 2 +MnO=100% is presumed, out of inclusions in the steel, is 20 nos./500 g or below.

First claim

The invention claimed is:

1. High cleanliness spring steel, comprising:
based on the total weight of the steel,
C: 1.2 mass % or below (not inclusive of 0%);
Si: 1.2-4 mass %;
Mn: 0.1-2.0 mass %;
Al: 0.01 mass % or below (not inclusive of 0%),
said spring steel comprising oxide-based inclusions with the width of 3 μm or above present in a surface layer side from a surface of a wire rod to a depth of ¼ of the diameter, wherein the content of the oxide-based inclusions satisfies an inequality relationship (1) below and the width is defined by a diameter of the inclusion in a direction perpendicular to an axial direction of a section comprising an axial center line of the wire rod;
wherein the oxide-based inclusions have:
a concentration of MgO of 5 mass % or below (inclusive of 0 mass %) based on the total weight of the inclusion; and
a concentration of MnO of 10 mass % or below (inclusive of 0 mass %) based on the total weight of the inclusion,
wherein: [Cn], [An] and [Sn] of CaO, Al 2 O 3 and SiO 2 in the oxide-based inclusions are respectively defined by (2)-(4) below;
the concentration of [Cn], [An] and [Sn] satisfy relationships of (5) and (6) below;
the melting point of the oxide-based inclusions of a CaO—Al 2 O 3 —SiO 2 three component system phase diagram, is 1,500° C. or below;
the oxide-based inclusions of the CaO—Al 2 O 3 —SiO 2 three component system phase diagram are defined by the area surrounded by lines A, B, and C of FIG. 4 of this Application, incorporated herein by reference; and
wherein: the concentrations of MgO, MnO, [Cn], [An], [Sn] are defined by an average value of oxide-based inclusions in the spring steel,
CaO+Al 2 O 3 +SiO 2 >80 (mass %)  (1)

[Cn](mass %)=[(CaO)/(CaO+Al 2 O 3 +SiO 2 )]×100  (2)

[An](mass %)=[(Al 2 O 3 )/(CaO+Al 2 O 3 +SiO 2 )]×100  (3)

[Sn](mass %)=[(SiO 2 )/(CaO+Al 2 O 3 +SiO 2 )]×100  (4)

[An]+4.29 [Sn]≦221.9 (mass %)  (5)

[An]≦30 (mass %)  (6).

2. The high cleanliness spring steel as set forth in claim 1 , further containing one or more kinds of elements selected from the group consisting of Cr, Ni, V, Nb, Mo, W, Cu, Ti, Li, Na, K and rare earth elements.

3. The high cleanliness spring steel as set forth in claim 1 , wherein the melting point of the oxide-based inclusions of the CaO—Al 2 O 3 —SiO 2 three component system phase diagram defined by the area surrounded by lines A, B, and C of FIG. 4 of this Application, incorporated by reference, is 1,400° C. or below.

4. High cleanliness spring steel according to claim 1 , consisting essentially of:
based on the total weight of the steel,
C: 1.2 mass % or below (not inclusive of 0%);
Si: 1.2-4 mass %;
Mn: 0.1-2.0 mass %;
Al: 0.01 mass % or below (not inclusive of 0%),
said spring steel comprising oxide-based inclusions with the width of 3 μm or above present in a surface layer side from a surface of a wire rod to a depth of ¼ of the diameter, wherein the content of the oxide-based inclusions satisfies an inequality relationship (1) below and the width is defined by a diameter of the inclusion in a direction perpendicular to an axial direction of a section comprising an axial center line of the wire rod;
wherein the oxide-based inclusions have:
a concentration of MgO of 5 mass % or below (inclusive of 0 mass %) based on the total weight of the inclusion; and
a concentration of MnO of 10 mass % or below (inclusive of 0 mass %) based on the total weight of the inclusion,
wherein: [Cn], [An] and [Sn] of CaO, Al 2 O 3 and SiO 2 in the oxide-based inclusions are respectively defined by (2)-(4) below;
the concentration of [Cn], [An] and [Sn] satisfy relationships of (5) and (6) below;
the melting point of the oxide-based inclusions of a CaO—Al 2 O 3 —SiO 2 three component system phase diagram, is 1,500° C. or below;
the oxide-based inclusions of the CaO—Al 2 O 3 —SiO 2 three component system phase diagram are defined by the area surrounded by lines A, B, and C of FIG. 4 of this Application, incorporated herein by reference; and
wherein: the concentrations of MgO, MnO, [Cn], [An], [Sn] are defined by an average value of oxide-based inclusions in the spring steel,
CaO+Al 2 O 3 +SiO 2 >80 (mass %)  (1)

[Cn](mass %)=[(CaO)/(CaO+Al 2 O 3 +SiO 2 )]×100  (2)

[An](mass %)=[(Al 2 O 3 )/(CaO+Al 2 O 3 +SiO 2 )]×100  (3)

[Sn](mass %)=[(SiO 2 )/(CaO+Al 2 O 3 +SiO 2 )]×100  (4)

[An]+4.29 [Sn]≦221.9 (mass %)  (5)

[An]≦30 (mass %)  (6).

Assignees

• Kobe Steel Ltd

Inventors

• Sugimura Tomoko
• Kimura Sei
• Sakamoto Koichi
• Yoshida Atsuhiko
• Inoue Takeshi

Classifications

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C21D2211/004

  Dispersions; Precipitations · CPC title

• C22C38/44

  with molybdenum or tungsten · CPC title

• C22C38/24

  with vanadium · CPC title

• C22C38/46 Primary

  with vanadium · CPC title