Chinese Bearing Steel
Bearing steel is the steel used to manufacture bearing balls, rollers, and rings. It is a high-tech product among steel materials. It is a key material required for major equipment manufacturing and national key engineering construction. It is a guarantee for high-end manufacturing. No other materials can completely replace it. Bearing steel has high and uniform hardness and wear resistance and high elastic extremity. The requirements for the uniformity of chemical composition, the content and distribution of non-metallic inclusions, and the distribution of carbides are very strict. It is one of the most stringent steel grades in all steel production. In 1976, the International Organization for Standardization ISO incorporated some general bearing steel numbers into international standards and divided the bearing steel into four categories: fully hardened bearing steel, surface hardened bearing steel, stainless bearing steel, high temperature bearing steel, totally of 17 steel numbers in four categories.
Fully hardened bearing steels are mainly high-carbon chromium steels, such as GCr15, with a carbon content of about 1% and a chromium content of about 1.5%. In order to improve the hardness, wear-resistance, and hardenability, some silicon, manganese, molybdenum, etc., are appropriately added, such as GCr15SiMn. This type of bearing steel has the largest output, accounting for more than 95% of all bearing steel output. Carburized bearing steel is a chromium, nickel, and molybdenum alloy structural steel with a carbon content of 0.08 to 0.23%. The rear surface of the bearing part is made of carbonitriding to improve its hardness and wear resistance. This steel is used for manufacturing large bearings that can bear strong impact loads, such as large rolling mill bearings, mining machinery bearings and railway vehicle bearings, etc. Stainless bearing steels include high-carbon chromium stainless bearing steels, such as 9Cr18, 9Cr18MoV, etc., and medium-carbon chromium stainless bearing steels, such as 4Cr13, etc., which are used to make stainless and corrosion-resistant bearings. High temperature bearing steel is used at high temperature (300～500℃), which requires steel to have certain red hardness and wear resistance at the service temperature. Most high-speed tool steels are used instead, such as W18Cr4V, W9Cr4V, W6Mo5Cr4V2, Cr14Mo4, and Cr4Mo4V.
China has become a major producer of bearing steel. Statistics from 36 companies of the Special Steel Association show that the crude steel output of China’s major high-quality special steel enterprises in 2017 was 3.0146 million tons. Xingcheng Special Steel, Xinye Steel, and Benxi Steel Steel rank among the top three in bearing steel output, accounting for 51% of the total domestic bearing steel output. Xingcheng Special Steel has an annual production capacity of 1 million tons of bearing steel, including more than 600,000 tons of high-end bearing steel. It has ranked first in the world in the production and sales of bearing steel for eight consecutive years.
Bearings are one of the important components directly related to the safety of equipment operation. To ensure that the bearings have sufficient safety, reliability, and long service life under specified conditions of use, bearing steels are required to have excellent performance and fatigue life.
The key index for evaluating the quality of bearing steel is the purity and uniformity of the material. The purity of a material means that there are as few inclusions in the material as possible. The uniformity of the material means that the inclusions and carbide particles in the material are small and dispersed. The purity of the bearing directly affects the fatigue life of the bearing. The early failure of the bearing is mostly due to the presence of larger particles of inclusions; the uniformity affects the deformation and the uniformity of the structure after the bearing heat treatment.
Improving the purity of bearing steel, especially reducing the oxygen content in the steel, can significantly extend the life of the bearing. The lower the oxygen content, the fewer oxide inclusions, the higher the purity, and the longer the fatigue life of the bearing steel. Element Ti remains in the steel to form multi-angular inclusions. These inclusions are easy to cause local stress concentration, fatigue cracks and have a direct impact on the fatigue life of the bearing steel. Therefore, it is necessary to control the generation of such inclusions.
As early as 2009, Chinese Xingcheng Special Steel commissioned a foreign third-party organization to carry out the fatigue test of bearing steel. The results showed that the fatigue life of Xingcheng Special Steel bearing steel was equivalent to that of bearing steel produced by world well-known steel factories.
| GB Standard | ASTM Standard | EN Standard | JIS Standard | User standards and mutual agreement |
| GCr15 GCr15SiMn G20CrNiMo G20CrNi2Mo GCr18Mo | 52100 SAE4320 SAE8620 | 100Cr6 100CrMn6 20NiCrMo2 | SUJ2, SUJ3 SNCM420 | SKF3、SKF3S、SUJ2S1 100CrMnSi6-4、100Cr6 SKF42、SKF48、S53CG SKF5、SKF6、SKF7 C56E2、SKF255 |