High-carbon bearing steel - Characteristics of group and properties
Bearing steel, or steel for rolling elements, is characterized by very high carbon content - about 1%. It is characterized by high hardness, high degree of purity of chemical composition, high hardening capacity, high strength and static fatigue and, in addition, adequate material durability. In this type of steel the main emphasis is on the wear resistance. Components (eg. rollers, rings, spheres) and other components of nearer applications are subject to continuous movement, contact with other components usually under high pressure.
In many situations, specific corrosion resistance and resistance for the higher temperatures of the given steels are required. In some situations, by the chemical composition it can be determined and assing the bearing steels under the tool steels. Bearing steels must have a high machinability, no deformation during heat treatment, minimal non-metallic inclusions and sulfur, phosphorus, oxygen as well as a limited susceptibility to surface decontamination.
Heat treatment and conditions of delivery of bearing steel
The bearing steels are supplied in a softened state with a finely structured spheroidal cementite structure in the form of bars, sheets, pipes, forgings or rings. In addition to the raw materials, bearing steels are present in the form of drawn, ground and peeled bars. Heat treatment is not the easiest, so it is done under special conditions by austenitization at a temperature of 820-840 ℃, later hardening in oil, and tempering at 180 ℃ for 1-2 hours. After finishing the heat treatment process, the product has a structure of lath martensitic and hardness of over 62 HRC.
Others steels used for the production of bearings
Apart from the group of bearing steel, for rolling bearings are often used other steels for carburization, such as 18CrNiMo7-6, 21CrNiMo2-2, 20Cr3, 20CrMo4, steels for surface hardening - 56Mn4, 70Mn4, stainless steels and corrosion resistant steels such as X89CrMoV18, X65Cr14 and high-speed steels 80MoCrV42-16, X82WMoCrV6-5-2, X75WCrV18-4-1.
Chemical composition and alloy additives
For hypereutectoid steel are used additives such as Chrome - Cr in the range of about 1.35-2.05%, Manganese - Mn, and Silicon - Si, increasing hardening capacity of the material. Carburizing steels in the case of these applications are easier for cold forming and have a good core ductility. Stainless steels can work at elevated temperatures.
Bars, tubes and plates made of bearing steel
The described bearing steels and steels for rolling bearings are defined by PN-74/H-84041, BN-72/H-0641-06, and PN-EN ISO 683-17, according to which the company provides: