Bearing rings and rolling elements materials

1) High carbon chromium bearing steel

High carbon chromium bearing steel specified in JIS is used as a general material in bearing rings (inner rings, outer rings) and rolling elements (balls, rollers).
Their chemical composition classified by steel type is given in "Table 13-1 Chemical composition of high carbon chromium bearing steel".
Among these steel types, SUJ 2 is generally used. SUJ 3, which contains additional Mn and Si, possesses high hardenability and is commonly used for thick section bearings.
SUJ 5 has increased hardenability, because it was developed by adding Mo to SUJ 3.
For small and medium size bearings, SUJ 2 and SUJ 3 are used, and for large size and extra-large size bearings with thick sections, SUJ 5 is widely used.
Generally, these materials are processed into the specified shape and then undergo hardening and annealing treatment until they attain a hardness of 57 to 64 HRC.

2) Case carburizing bearing steel (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.
For this purpose, chromium steel and nickel-chromium-molybdenum steel are used as materials.
Typical steel materials are shown in "Table 13-2 Chemical composition of case carburizing bearing steel".

3) Steel for Standard JTEKT Specification Bearings

In general terms, it is known that the nonmetallic inclusions contained in materials are harmful to the rolling contact fatigue life.
At JTEKT, to reduce the amount of nonmetallic inclusions, which are harmful to the fatigue life, we set the chemical compounds of the bearing steel in a proprietary manner. As a result, JTEKT standard bearings have a life that is approximately twice as long as the general bearings that are targeted by JIS B 1518 (and ISO 281).
Therefore, the basic dynamic load ratings of JTEKT standard bearings are 1.25 times the dynamic load ratings established in JIS B 1518 (and ISO 281).
This steel for standard JTEKT specification bearings is not applied to the special application bearings in this general catalog. If you require special application bearings with long lives, contact JTEKT.

4) Other

For special applications, the special heat treatment shown below can be used according to various usage conditions.

[Extremely high reliability]

• SH bearings ¹⁾
  By using the heat treatment technology developed by JTEKT to perform special heat treatment on high carbon chromium bearing steel, we have improved the surface hardness of these products and provided them with compressive residual stress, which has led to high reliability especially in terms of resistance to foreign matter.
• KE bearings ²⁾
  By using the heat treatment technology developed by JTEKT to perform special heat treatment on carburized bearing steel, we have improved the surface hardness of these products and adjusted their amount of residual austenite, which has led to high reliability especially in terms of resistance to foreign matter.

1) Acronym of Special Heat treatment
2) Acronym of Koyo EXTRA-LIFE Bearing

Table 13-1 Chemical composition of high carbon chromium bearing steel

[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 those listed in this table.

Table 13-2 Chemical composition of case carburizing bearing steel