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Koyo Technical Information

10. Materials

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

Standard Code Chemical composition (%)
C Si Mn P S Cr Mo
JIS G 4805 SUJ 2 0.95 – 1.10 0.15 – 0.35 Not more
than 0.50		 Not more
than 0.025		 Not more
than 0.025		 1.30 – 1.60 –
SUJ 3 0.95 – 1.10 0.40 – 0.70 0.90 – 1.15 Not more
than 0.025		 Not more
than 0.025		 0.90 – 1.20 –
SUJ 5 0.95 – 1.10 0.40 – 0.70 0.90 – 1.15 Not more
than 0.025		 Not more
than 0.025		 0.90 – 1.20 0.10 – 0.25
SAEJ 404 52100 0.98 – 1.10 0.15 – 0.35 0.25 – 0.45 Not more
than 0.025		 Not more
than 0.025		 1.30 – 1.60 Not 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

Standards Code Chemical composition (%)
C Si Mn P S Ni Cr Mo
JIS G 4104 SCr 415 0.13 – 0.18 0.15 – 0.35 0.60 – 0.85 Not more than 0.030 Not more than 0.030 – 0.90 – 1.20 –
SCr 420 0.18 – 0.23 0.15 – 0.35 0.60 – 0.85 Not more than 0.030 Not more than 0.030 – 0.90 – 1.20 –
JIS G 4105 SCM 420 0.18 – 0.23 0.15 – 0.35 0.60 – 0.85 Not more than 0.030 Not more than 0.030 – 0.90 – 1.20 0.15 – 0.30
JIS G 4103 SNCM 220 0.17 – 0.23 0.15 – 0.35 0.60 – 0.90 Not more than 0.030 Not more than 0.030 0.40 – 0.70 0.40 – 0.65 0.15 – 0.30
SNCM 420 0.17 – 0.23 0.15 – 0.35 0.40 – 0.70 Not more than 0.030 Not more than 0.030 1.60 – 2.00 0.40 – 0.65 0.15 – 0.30
SNCM 815 0.12 – 0.18 0.15 – 0.35 0.30 – 0.60 Not more than 0.030 Not more than 0.030 4.00 – 4.50 0.70 – 1.00 0.15 – 0.30
SAE J 404 5120 0.17 – 0.22 0.15 – 0.35 0.70 – 0.90 Not more than 0.030 Not more than 0.040 – 0.70 – 0.90 –
8620 0.18 – 0.23 0.15 – 0.35 0.70 – 0.90 Not more than 0.035 Not more than 0.040 0.40 – 0.70 0.40 – 0.60 0.15 – 0.25
4320 0.17 – 0.22 0.15 – 0.30 0.45 – 0.65 Not more than 0.025 Not more than 0.025 1.65 – 2.00 0.40 – 0.60 0.20 – 0.30
a.3. Other materials

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

Chemical composition of stainless steel

Standard Code Chemical composition (%)
C Si Mn P S Cr Mo
JIS G4303 SUS 440C 0.95 – 1.20 Not more than 1.00 Not more than 1.00 Not more than 0.040 Not more than 0.030 16.00 – 18.00 Not more than 0.75

 

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

Long life bearings Material Characteristics and effect Performance (Compared with conventional bearings) Applicable bearings Applications
Life in clean lubricant Life in contaminated lubricant Ball 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 longer Same
  • For Automobile
GTS
(Greater toughness steel bearings)		 Through hardened steel
  • Significant toughness and matrix strength by controlling alloy element
 6 times or longer 2 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 longer 2 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 longer 10 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 longer 10 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

Standards Code Chemical composition (%)
C Si Mn P S Ni Cr
JIS G 3141 SPCC Not more than 0.12 – Not more than 0.50 Not more than 0.040 Not more than 0.045 – –
JIS G 3131 SPHC Not more than 0.15 – Not more than 0.60 Not more than 0.050 Not more than 0.050 – –
BAS 361 SPB 2 0.13 – 0.20 Not more than 0.04 0.25 – 0.60 Not more than 0.030 Not more than 0.030 – –
JIS G 4305 SUS 304 Not more than 0.08 Not more than 1.00 Not more than 2.00 Not more than 0.045 Not more than 0.030 8.00 ~ 10.50 18.00 ~ 20.00
JIS G 4051 S 25 C 0.22 – 0.28 0.15 – 0.35 0.30 – 0.60 Not more than 0.030 Not more than 0.035 – –

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

Standards Code Cu Zn Mn Fe Al Sn Ni Impurity
Pb Si
JIS H 5102 HBsC 1 Not more than 55.0 The remainder Not more than 1.5 0.5 ~ 1.5 0.5 ~ 1.5 Not more than 1.0 Not more than 1.0 Not more than 0.4 Not more than 0.1