Nitrided steel member and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-9783879-B2
Application number	US-201314394423-A
Country	US
Kind code	B2
Filing date	Apr 17, 2013
Priority date	Apr 18, 2012
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

A nitrided steel member including an iron nitride compound layer formed on a surface of a steel member having predetermined components, wherein: in X-ray diffraction peak intensity IFe 4 N (111) of a (111) crystal plane of Fe 4 N and X-ray diffraction peak intensity IFe 3 N (111) of a (111) crystal plane of Fe 3 N, which are measured on a surface of the nitrided steel member by X-ray diffraction, an intensity ratio expressed by IFe 4 N (111)/{IFe 4 N (111)+IFe 3 N (111)} is 0.5 or more; Vickers hardness of the iron nitride compound layer is 900 or less, Vickers hardness of a base metal immediately under the iron nitride compound layer is 700 or more, and a difference between the Vickers hardness of the iron nitride compound layer and the Vickers hardness of the base metal is 150 or less; and a thickness of the iron nitride compound layer is 2 to 17 μm.

First claim

The invention claimed is:

1. A nitrided steel member comprising an iron nitride compound layer formed on a surface of a base metal
which contains, by mass %, C: 0.05 to 0.14%, Si: 0.10 to 0.30%, Mn: 0.4 to 1.4%, Cr: 0.9 to 1.9%, Mo: 0 to 0.50%, V: 0 to 0.40%, Al: 0.01 to 0.14%, and S: 0.005 to 0.030%,
whose Hs value expressed by the following expression 1 is 1.19 or more,
Hs value=(−342.1×C+23.5×Mn+125.0×Cr+14.4×Mo+208.3×V+346.4×Al)/100  expression 1,

whose Hc value expressed by the following expression 2 is 3.76 or less,
Hc value=(156.1×C+54.7×Mn+158.4×Cr+146.5×Mo+33.8×V+418.6×Al)/100  expression 2,

where C, Mn, Cr, Mo, V, and Al represent values of mass % of the respective elements, and
in which the balance is made of Fe and impurities, with P, N, and O in the impurities being P: 0.030% or less, N: 0.008% or less, and O: 0.0030% or less,
wherein, in X-ray diffraction peak intensity IFe 4 N (111) of a (111) crystal plane of Fe 4 N and X-ray diffraction peak intensity IFe 3 N (111) of a (111) crystal plane of Fe 3 N, which are measured on the surface of the nitrided steel member by X-ray diffraction, an intensity ratio expressed by IFe 4 N (111)/{IFe 4 N (111)+IFe 3 N (111)} is 0.5 or more,
wherein Vickers hardness of the iron nitride compound layer is 900 or less, Vickers hardness of the base metal immediately under the iron nitride compound layer is 700 or more, and a difference between the Vickers hardness of the iron nitride compound layer and the Vickers hardness of the base metal is 150 or less, and
wherein a thickness of the iron nitride compound layer is 2 to 17 μm.

2. The nitrided steel member according to claim 1 , being a gear used in a transmission.

3. A manufacturing method of a nitrided steel member, the method comprising applying a nitriding treatment to a base metal in an atmosphere of nitriding treatment gas in which a ratio of a partial pressure of NH 3 gas is 0.08 to 0.34, a ratio of a partial pressure of H 2 gas is 0.54 to 0.82, and a ratio of a partial pressure of N 2 gas is 0.09 to 0.18 when a total pressure is defined as 1, with a flow velocity of the nitriding treatment gas on a surface of the base metal being set to 1 m/s or more, and with a temperature being set to 500 to 620° C., to thereby form an iron nitride compound layer with a 2 to 17 μm thickness on the surface of the base metal,
the steel member being a member
which contains, by mass %, C: 0.05 to 0.14%, Si: 0.10 to 0.30%, Mn: 0.4 to 1.4%, Cr: 0.9 to 1.9%, Mo: 0 to 0.50%, V: 0 to 0.40%, Al: 0.01 to 0.14%, and S: 0.005 to 0.030%,
whose Hs value expressed by the following expression 1 is 1.19 or more,
Hs value=(−342.1×C+23.5×Mn+125.0×Cr+14.4×Mo+208.3×V+346.4×Al)/100  expression 1,

whose Hc value expressed by the following expression 2 is 3.76 or less,
Hc value=(156.1×C+54.7×Mn+158.4×Cr+146.5×Mo+33.8×V+418.6×Al)/100  expression 2,

where C, Mn, Cr, Mo, V, and Al represent values of mass % of the respective elements, and
in which the balance is made of Fe and impurities, with P, N, and O in the impurities being P: 0.030% or less, N: 0.008% or less, and O: 0.0030% or less.

4. The manufacturing method of the nitrided steel member according to claim 3 , wherein a time of the nitriding treatment is within a range over 0.5 hours and less than ten hours.

Assignees

• Dowa Thermotech Co Ltd
• Honda Motor Co Ltd
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Shimizu Yuichiro
• Kobayashi Atsushi
• Maeda Susumu
• Kanayama Masao
• Imataka Hideki
• Yuya Masato
• Gyotoku Yuya
• Akimoto Kiyotaka

Classifications

• C22C38/24

  with vanadium · CPC title

• C21D2201/05

  Grain orientation · CPC title

• C21D2211/004

  Dispersions; Precipitations · CPC title

• F16H55/06

  Use of materials; Use of treatments of toothed members or worms to affect their intrinsic material properties · CPC title

• C22C38/04

  containing manganese · CPC title