US 9,809,875 B2
Case hardening steel with excellent fatigue properties
Masayuki Hashimura, Tokyo (JP); Masafumi Miyazaki, Tokyo (JP); Takashi Fujita, Tokyo (JP); and Hideaki Yamamura, Tokyo (JP)
Assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION, Tokyo (JP)
Appl. No. 14/422,825
Filed by NIPPON STEEL & SUMITOMO METAL CORPORATION, Tokyo (JP)
PCT Filed Oct. 18, 2013, PCT No. PCT/JP2013/078328
§ 371(c)(1), (2) Date Feb. 20, 2015,
PCT Pub. No. WO2014/061784, PCT Pub. Date Apr. 24, 2014.
Claims priority of application No. 2012-231597 (JP), filed on Oct. 19, 2012.
Prior Publication US 2015/0191808 A1, Jul. 9, 2015
Int. Cl. C22C 38/28 (2006.01); C22C 38/50 (2006.01); C22C 38/14 (2006.01); C21C 7/10 (2006.01); C22C 38/00 (2006.01); C21D 1/06 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/20 (2006.01); C22C 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/32 (2006.01); C22C 38/40 (2006.01); C21C 7/064 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C21D 9/40 (2006.01)
CPC C22C 38/50 (2013.01) [C21C 7/064 (2013.01); C21C 7/10 (2013.01); C21D 1/06 (2013.01); C22C 38/00 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C22C 38/40 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C21D 9/40 (2013.01)] 3 Claims
OG exemplary drawing
 
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/mm2 or less.