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 a wall thickness between 3.5 and 20 mm. They are available in two precision levels: standard and high. Bearing steel, on the other hand, is a specialized type of steel used to manufacture bearing components such as balls, rollers, and rings. Since bearings operate under extreme pressure and friction, the steel must exhibit high and uniform hardness, excellent wear resistance, and a strong elastic limit. The chemical composition, non-metallic inclusions, and carbide distribution in bearing steel must be strictly controlled, making it one of the most demanding types of steel in the industry.
The physical properties of bearing steel are evaluated through microscopic structure analysis, decarburization layer depth, non-metallic inclusion content, and low-magnification structure inspection. Normally, the steel is delivered in a hot-rolled annealed or cold-drawn annealed condition, and the delivery status should be clearly specified in the contract. The low-magnification inspection must ensure that there are no shrinkage cavities, subsurface bubbles, white spots, or micro-pores. Central looseness and general looseness should not exceed 1.5, and segregation levels must not go beyond grade 2. The annealed structure should consist of uniformly distributed fine pearlite. Additionally, the depth of decarburization, non-metallic inclusions, and carbide distribution must meet national standards.
For delivery, steel with a diameter less than 20 mm is usually packed, while larger diameters may be delivered bare. Packaging specifications depend on the agreement between the buyer and seller, including options like hexagonal packaging, length tolerances, and additional export packaging. Cold-drawn steel pipes are generally coated with rust-preventative oil. However, if domestic manufacturers require urgent delivery, they might not be coated, but this could necessitate degreasing before processing the bearing rings. Before shipment, each batch should include a quality certificate specifying the steel grade, furnace number, weight, dimensions, chemical composition, testing standards, and test results.
Sources: Internal documentation, industry standards, and technical specifications.
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