Bearing steel pipes are seamless steel tubes, either hot-rolled or cold-drawn, specifically designed for the production of standard rolling bearing rings. These pipes typically have an outer diameter ranging from 25 to 180 mm and wall thicknesses between 3.5 to 20 mm. They are available in two levels of precision: ordinary and high. Bearing steel is a specialized type of alloy used to manufacture components such as balls, rollers, and bearing rings. Due to the extreme pressure and friction these bearings endure during operation, the steel must exhibit high and uniform hardness, excellent wear resistance, and a high elastic limit. The chemical composition, non-metallic inclusion content, and carbide distribution in bearing steel are strictly controlled, making it one of the most demanding types of steel in the industry.
The physical properties of bearing steels are primarily evaluated through microstructure analysis, decarburization layer depth, non-metallic inclusions, and low-magnification structures. Normally, the material is delivered in a hot-rolled annealed or cold-drawn annealed condition, as specified in the contract. The low-magnification inspection must confirm the absence of shrinkage, subsurface bubbles, white spots, and micro-porosity. Central looseness and general looseness should not exceed 1.5, while segregation levels must be no more than 2. The annealed structure should consist of uniformly distributed fine pearlite. Additionally, the decarburization depth, non-metallic inclusions, and carbide distribution must meet relevant national standards.
In terms of delivery, steel pipes with a diameter less than 20 mm are usually packed, while those over 20 mm may be delivered bare. Packaging requirements vary depending on the contract, and options include hexagonal packaging, length tolerances, and additional export packaging. Cold-drawn steel pipes are generally coated with rust-preventive oil. However, if domestic manufacturers require urgent delivery, they may opt for non-rust-proof versions, though this could necessitate degreasing before processing the bearing rings. Before shipment, each batch must come with a quality assurance certificate that includes details such as the steel grade, furnace number, weight, dimensions, chemical composition, testing standards, and test results.
Sources: Internal technical specifications and industry standards.
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