Standard ball bearings steel with content of carbon and chromium was selected and hardended to withstand the intense pressure between the rolling element and bearing rings.
Carbonitriding on both inner and outer rings is a basic hardening process for many TPI ball bearings suppliers. Through this special heat treatment, hardness on the raceway surface is increased; which reduces wear accordingly.
Ultra-clean steel is available in some of TPI standard ball bearings' product series now, higher wear-resistance is obtained accordingly. Since contact fatigue is often caused by hard non-metallic inclusions, bearings nowadays require exceptional levels of cleanliness.