NSK bearing rings and rolling elements of rolling bearings are subjected to repetitive high pressure with a small amount of sliding. The cages are subjected to tension and compression and sliding contact with the rolling elements and either or both of the NSK bearing rings.
Therefore, the materials used for the rings, rolling elements, and cages require the following characteristics:
- High rolling contact fatigue strength
- High hardness
- High wear resistance
- High dimensional stability
- High mechanical strength
Other necessary characteristics, such as easy production, shock and heat resistance, and corrosion resistance, are required depending on individual applications.
Materials for NSK bearing rings and rolling elements
Preimarily, high carbon chromium bearing steel is used for the bearing rings and rolling elements.
| Standard | Symbols | Chemical composition (%) | ||||||
|---|---|---|---|---|---|---|---|---|
| C | Si | Mn | P | S | Cr | Mo | ||
| JIS G 4805 | SUJ 2 | 0.95 to 1.10 | 0.15 to 0.35 | Less than 0.50 | Less than 0.025 | Less than 0.025 | 1.30 to 1.60 | - |
| SUJ 3 | 0.95 to 1.10 | 0.40 to 0.70 | 0.90 to 1.15 | Less than 0.025 | Less than 0.025 | 1.90 to 1.20 | - | |
| SUJ 4 | 0.95 to 1.10 | 0.15 to 0.35 | Less than 0.50 | Less than 0.025 | Less than 0.025 | 1.30 to 1.60 | 0.10 to 0.25 | |
| ASTM A 295 | 52100 | 0.93 to 1.05 | 0.15 to 0.35 | 0.25 to 0.45 | Less than 0.025 | Less than 0.015 | 1.35 to 1.60 | Less than 0.10 |
Most NSK bearings are made of SUJ2 among the JIS steel types listed in table above, while the NSK larger bearings generally use SUJ3. The chemical composition of SUJ2 is approximately the same as AISI 52100 specified in the USA, DIN 100 Cr6 in Germany, and BS 535A99 in England.
For NSK bearings that are subjected to very severe shock loads, carburized low-carbon alloy steels such as chrome steel, chrome molybdenum steel, nickel chrome molybdenum steel, etc. are often used. Such steels, when they are carburized t othe proper depth and have sufficient surface hardness, are more shock resistant than normal, through-hardened bearing steels because of the softer energy-absorbing core.
NSK uses highly pure vacuum-degassed bearing steel containing a minimum of oxygen, nitrogen, and hydrogen compound impurities. The rolling fatigue life of NSK bearings has been remarkably improved using this material combined with the appropriate heat treatment. For special purpose bearings, high temperature bearing steel, which has superior heat resistance, and stainless steel having good corrosion resistance may be used.