Case hardening steel with excellent fatigue properties

Patent metadata

Field	Value
Publication number	US-9809875-B2
Application number	US-201314422825-A
Country	US
Kind code	B2
Filing date	Oct 18, 2013
Priority date	Oct 19, 2012
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A case hardening steel includes as a chemical composition, by mass %, C: 0.10% to 0.40%, Si: 0.01% to 0.80%, Mn: 0.1% to 1.5%, Cr: 0.35% to 2.0%, Al: 0.01% to 0.05%, REM: 0.0001% to 0.050%, O: 0.0001% to 0.0030%, Ca: 0.0050% or less as necessary, Ti: less than 0.005%, N: 0.015% or less, P: 0.03% or less, S: 0.01% or less, and the balance consists of Fe and impurities. The case hardening steel also includes a composition inclusion which is an inclusion containing REM, O, S, and Al, or an inclusion containing REM, Ca, O, S, and Al, to which TiN is adhered.

First claim

The invention claimed is:

1. A case hardening steel comprising as a chemical composition, by mass %:
C: 0.10% to 0.40%;
Si: 0.01% to 0.80%;
Mn: 0.1% to 1.5%;
Cr: 0.35% to 2.0%;
Al: 0.01% to 0.05%;
REM: 0.0001% to 0.050%;
O: 0.0001% to 0.0030%;
Ti: less than 0.005%;
N: 0.015% or less;
P: 0.03% or less;
S: 0.01% or less; and
the remainder comprising Fe and impurities,
wherein the case hardening steel includes a composite inclusion which is an inclusion containing REM, O, S, and Al, to which TiN is adhered, and
the sum of a number density of TiN having a maximum diameter of 1 μm or more which independently exists without adhesion to the inclusion, and a number density of MnS having a maximum diameter of 10 μm or more is 5 pieces/mm 2 or less.

2. A case hardening steel comprising as a chemical composition, by mass %:
C: 0.10% to 0.40%;
Si: 0.01% to 0.80%;
Mn: 0.1% to 1.5%;
Cr: 0.35% to 2.0%;
Al: 0.01% to 0.05%;
Ca: 0.0050% or less;
REM: 0.0001% to 0.050%;
O: 0.0001% to 0.0030%;
Ti: less than 0.005%;
N: 0.015% or less;
P: 0.03% or less;
S: 0.01% or less; and
the remainder comprising Fe and impurities,
wherein the case hardening steel includes a composite inclusion which is an inclusion containing REM, Ca, O, S, and Al, to which TiN is adhered, and
the sum of a number density of TiN having a maximum diameter of 1 μm or more which independently exists without adhesion to the inclusion, and a number density of MnS having a maximum diameter of 10 μm or more is 5 pieces/mm 2 or less.

3. The case hardening steel according to claim 1 or 2 , further comprising as the chemical composition, one or more kinds of elements selected from the group consisting of, by mass %;
V: 0.70% or less;
Mo: 1.00% or less;
W: 1.00% or less;
Ni: 3.50% or less;
Cu: 0.50% or less;
Nb: less than 0.050%; and
B: 0.0050% or less.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Hashimura Masayuki
• Miyazaki Masafumi
• Fujita Takashi
• Yamamura Hideaki

Classifications

• C22C38/50 Primary

  with titanium or zirconium · CPC title

• C22C38/02

  containing silicon · CPC title

• C22C38/002

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

• C21D9/40

  for rings; for bearing races · CPC title

• C22C38/06

  containing aluminium · CPC title