Specifications: Unlike the material used in the outer ring of the rear wheel which undergoes induction hardening, this grade of steel is hardened through rapid quenching in oil and a unified tempering process. Given the general operating conditions of bearings, characterized by high localized stresses and cyclic loading, this steel must not only offer high surface hardness and dimensional stability but also exhibit high resistance to fatigue crack growth, thereby ensuring long service life.
These characteristics are achieved through: :

• Increasing the steel's purity and reducing unwanted elements
• Decreasing the amount of dissolved oxygen in the molten steel, thus reducing the level of oxide impurities
• Reducing the number, size, and shape of non-oxide inclusions
• Ensuring the uniformity of the steel's structure

To achieve these key factors, the steel must be exceptionally clean, with minimal impurities such as phosphorus, sulfur, silicon, and aluminum that can form non-metallic inclusions when combined with the oxygen in the steel. These inclusions act as weak points in the steel, initiating fatigue cracks. Hence, the oxygen content in bearing steel production must be below 15 PPM, and impurities like aluminum and titanium should be removed or minimized to the greatest extent possible.

Typically, this grade of steel undergoes secondary metallurgy operations, in addition to the addition of alloying elements like chromium and precise melt analysis, to minimize oxygen content under vacuum. Alternatively, single-ingot melting from under the ingot can be used to achieve minimal impurities in the steel. Below is a schematic of the bearing steel production process. This process is currently available at Iran Alloy Steel Company, but its implementation requires stringent technical follow-ups and the definition of strict standards to ensure quality during initial localization.

The shape of raw materials for bearing ring production varies slightly depending on the application. For industrial bearings and light loads with high speeds in diameters approximately below 40 mm, seamless tube sections and machining methods are used.

For large dimensions and heavy loads in heavy machinery, generators, and automotive wheel hub bearings, due to safety reasons, combined forging and hot ring rolling methods are used.

Microstructure upon Delivery: : Spheroidizing annealing with a maximum hardness of 207 HB and minimal decarburization layer. Due to the high carbon and chromium content, these conditions are necessary to achieve the required flexibility and formability in subsequent hot forging operations.