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Koyo Technical Information

a. Outer/Inner ring and rolling element materials
a.1. High carbon chromium bearing steel

As material of bearing rings and rolling elements, high-carbon chromium bearing steel specified in JIS G4805 is used. The steel is hardened and tempered before use.

SUJ2 – Most common bearing steel.
SUJ3 -Has more manganese than SUJ2 and therefore has better tempering characteristics. Used for medium-size and large-size bearings.
SUJ5 – Made by adding molybdenum to SUJ3, improving tempering characteristics further. It is used for thick-section products and very large bearings.

Table 10-1 Chemical composition of high carbon chromium bearing steel

StandardCodeChemical composition (%)
CSiMnPSCrMo
JIS G 4805SUJ 20.95 – 1.100.15 – 0.35Not more
than 0.50
Not more
than 0.025
Not more
than 0.025
1.30 – 1.60
SUJ 30.95 – 1.100.40 – 0.700.90 – 1.15Not more
than 0.025
Not more
than 0.025
0.90 – 1.20
SUJ 50.95 – 1.100.40 – 0.700.90 – 1.15Not more
than 0.025
Not more
than 0.025
0.90 – 1.200.10 – 0.25
SAEJ 404521000.98 – 1.100.15 – 0.350.25 – 0.45Not more
than 0.025
Not more
than 0.025
1.30 – 1.60Not more
than 0.06

[Remark] As for bearings which are induction hardened, carbon steel with a high carbon content of 0.55 to 0.65 % is used in addition to listed in this table.

a.2. Case hardened steel

When a bearing receives heavy impact loads, the surface of the bearing should be hard and the inside soft. Such materials should possess a proper amount of carbon, dense structure, and carburizing case depth on their surface, while having proper hardness and fine structure internally.

Table 10-2 Chemical composition of case hardened steel

StandardsCodeChemical composition (%)
CSiMnPSNiCrMo
JIS G 4104SCr 4150.13 – 0.180.15 – 0.350.60 – 0.85Not more than 0.030Not more than 0.0300.90 – 1.20
SCr 4200.18 – 0.230.15 – 0.350.60 – 0.85Not more than 0.030Not more than 0.0300.90 – 1.20
JIS G 4105SCM 4200.18 – 0.230.15 – 0.350.60 – 0.85Not more than 0.030Not more than 0.0300.90 – 1.200.15 – 0.30
JIS G 4103SNCM 2200.17 – 0.230.15 – 0.350.60 – 0.90Not more than 0.030Not more than 0.0300.40 – 0.700.40 – 0.650.15 – 0.30
SNCM 4200.17 – 0.230.15 – 0.350.40 – 0.70Not more than 0.030Not more than 0.0301.60 – 2.000.40 – 0.650.15 – 0.30
SNCM 8150.12 – 0.180.15 – 0.350.30 – 0.60Not more than 0.030Not more than 0.0304.00 – 4.500.70 – 1.000.15 – 0.30
SAE J 40451200.17 – 0.220.15 – 0.350.70 – 0.90Not more than 0.030Not more than 0.0400.70 – 0.90
86200.18 – 0.230.15 – 0.350.70 – 0.90Not more than 0.035Not more than 0.0400.40 – 0.700.40 – 0.600.15 – 0.25
43200.17 – 0.220.15 – 0.300.45 – 0.65Not more than 0.025Not more than 0.0251.65 – 2.000.40 – 0.600.20 – 0.30
a.3. Other materials

1) Stainless steel is used as satisfactory materials for high corrosion resistance.

Chemical composition of stainless steel

StandardCodeChemical composition (%)
CSiMnPSCrMo
JIS G4303SUS 440C0.95 – 1.20Not more than 1.00Not more than 1.00Not more than 0.040Not more than 0.03016.00 – 18.00Not more than 0.75

 

2) For special applications, the following materials are used, according to operational conditions. Please contact Koyo.

Long life bearingsMaterialCharacteristics and effectPerformance (Compared with conventional bearings)Applicable bearingsApplications
Life in clean lubricantLife in contaminated lubricantBall bearing
HRS
(High refining steel bearings)
Through hardened steel
(SUJ2)
  • Equivalent to special remelting steel
  • Long life by minimizing inclusions
  • HRS with SH treatment is much better
3 times or longerSame
  • For Automobile
GTS
(Greater toughness steel bearings)
Through hardened steel
  • Significant toughness and matrix strength by controlling alloy element
6 times or longer2 times or longer
  • Extra long life under heavy load
KUJ7
(Medium heat resistant steel bearings)
  • High resistance against hardness reduction by tempering
7 times or longer(at 150℃)2 times or longer
  • For continuous casting equipment
  • For turbocharger
CH213
(Carburized steel for larger size bearings)
Carburized steel
  • High resistance against hardness reduction by tempering
  • Optimized alloy element
4 times or longer2 times or longer
  • For steel and other rolling mills
SH
(Special heat treated bearings)
Through hardened steel
  • High surface hardness
  • Adequate resistance to wear
6 times or longer10 times or longer
  • In contaminated lubricant such as differential or transmission gear boxes
KE
(New hi-cap tapered roller bearings)
Carburized steel
  • High surface hardness
  • Controlled retained austenite
2 times or longer10 times or longer
b. Materials used for cages

The cage is closely related to the performance and reliability of bearings. It is, therefore, very important to select appropriate cage material.

1) Metal cages are most common, made from steel or copper alloy. Representative cage materials and their chemical components are given in the table below.

2) In addition to metal cages, those produced by machining phenol resin or by molding synthetic resin are also common. Polyacetal, polyamide (Nylon 66 and Nylon 46), and fluororesin are popular materials. For cage production, these resins are reinforced by glass fiber or carbon fiber.

Table 10-3 Chemical composition of pressed cage steel sheet and machined cage carbon steel

StandardsCodeChemical composition (%)
CSiMnPSNiCr
JIS G 3141SPCCNot more than 0.12Not more than 0.50Not more than 0.040Not more than 0.045
JIS G 3131SPHCNot more than 0.15Not more than 0.60Not more than 0.050Not more than 0.050
BAS 361SPB 20.13 – 0.20Not more than 0.040.25 – 0.60Not more than 0.030Not more than 0.030
JIS G 4305SUS 304Not more than 0.08Not more than 1.00Not more than 2.00Not more than 0.045Not more than 0.0308.00 ~ 10.5018.00 ~ 20.00
JIS G 4051S 25 C0.22 – 0.280.15 – 0.350.30 – 0.60Not more than 0.030Not more than 0.035

Table 10-4  Chemical composition of high-tensile brass casting of machined cages (%)

StandardsCodeCuZnMnFeAlSnNiImpurity
PbSi
JIS H 5102HBsC 1Not more than 55.0The remainderNot more than 1.50.5 ~ 1.50.5 ~ 1.5Not more than 1.0Not more than 1.0Not more than 0.4Not more than 0.1