The GCR15 designation used in China is almost equivalent (with very little composition deffierence) to the following standards in other countries.
Gcr15 (AISI 52100) is an excellent general purpose bearing steel. Due to its excellent hardness and wear resistance, it exhibits good fatigue life in rolling element bearings. However, the corrosion resistance of chrome steel is poor because of the low chromium content. The surfaces of the bearings must be protected with a coating of rust inhibitor or oil to stop oxidation.
Grade 440C stainless steels are high carbon steels, which attain the highest hardness, wear resistance and strength of all stainless steel grades after heat treatment. These properties make this grade suitable for applications such as valve components and ball bearings. The level of carbon content means the components are magnetic. The corrosion resistance is "good", when 440C material is exposed to fresh water and mild chemicals, however, corrosion can occur in highly acidic or alkaline environment. This material is primarily used by US bearing manufacturers.
Miniature bearings made from conventional 440C stainless steel will be slightly noisy because the large carbides that normally concentrate at the grain boundaries are exposed in the raceway finishing process. Larger bore bearings are not as affected by this condition. Bearings made from 400 series stainless steel can operate at higher temperatures than chrome steel, up to 250°C continuous. Bearings made from this material are generally more expensive than chrome steel bearings.
Grade 440 stainless steels exhibit excellent resistance to mild acids, alkalis, foods, fresh water and air. A smooth polished surface also helps grade 440 steels resist corrosion in tempered, passivated and hardened conditions.
Grade 440C steels exhibit corrosion resistance similar to that of grade 304 steels.
AISI type 304 stainless steel materials are used where good corrosion resistance is important, but hardness is not. The 304 Stainless Steel material is non-magnetic (or slightly magnetic), it has better corrosion resistance compared to 440 Stainless, but it is softer than 440C, it may also have a poorer apperance. However, the 304 stainless offers good resistance to atmospheric corrosion, dyes, food environments, sterilizing solutions and many organic and inorganic materials. Type 304 bearings are normally used in medical applications and food processing. Bearings made of 304 are only suitable for low speed low load applications.
316 stainless steel is a higher-grade stainless steel than 304 and is more resistant to corrosion and pitting. It is often used in applications where corrosion resistance is important, such as in marine environments and in the chemical industry.
Silicon Nitride (Si3N4) Ceramic Balls are formed from a new material suitable for applications where high loads, high speeds and extreme temperatures are factors. Long life and the need for minimal lubrication make this material appropriate for extreme applications. Silicon Nitirde is non-porous, non-magentic, non corrosive, lighter than steel and, in ball form, is harder than steel. Because ceramic balls are non-porous they are virtually frictionless and are capable of spinning faster than steel balls.