GB/T 29913-2025Medium carbon alloy bearing steel (English PDF)

5.1 Smelting method

The steel shall be smelted in an electric furnace (or converter) and subjected to ladle refining and vacuum degassing treatments.

5.2 Delivery condition

5.2.1 Continuously cast round billets and ingots shall be delivered in the as-cast

condition. Hot-rolled bars shall be delivered in the hot-rolled condition. Forged bars shall be delivered in the forged condition.

5.2.2 Upon mutual agreement between the supplier and the purchaser, and as specified

in the contract, steel materials may also be delivered in the annealed condition.

6.1 Designation and chemical composition

6.1.1 The steel designation and chemical composition (ladle analysis) shall comply with

the requirements specified in Table 1.

6.1.2 The oxygen content (mass fraction) in the steel shall not exceed 0 0015%, and the hydrogen content (mass fraction) shall not exceed 0.00020%.

6.1.3 The contents (mass fractions) of tin, arsenic, antimony, lead, and bismuth in the steel shall each not exceed 0.010%.

Table 1 -- Designation and chemical composition

6.1.4 The allowable deviations in the chemical composition of the finished product shall

comply with the provisions of Table 2.

The austenitic grain size of the steel shall be Grade 5 or finer. If the supplier can guarantee compliance, grain size inspection may be omitted.

6.6 Surface quality

6.6.1 The surface of continuously cast round billets shall be free from visually

discernible scabs, blowholes, pinholes, inclusions, and laps. Shall any of the aforementioned defects be present, they must be removed. The cleared areas shall be smooth and free of sharp edges. The depth of removal, measured from the actual surface of the continuously cast round billet, shall not exceed 4% of the diameter, with a maximum removal depth not exceeding 12 mm. The ratio of depth to width to length shall be no less than 1.6.8.On any given cross-section, the maximum removal depth shall occur at no more than one location. The presence of folds and pits with a depth not exceeding 3.0 mm, raised ridges with a height not exceeding 3.0 mm, and mechanical scratches or indentations with a depth not exceeding 2.0 mm is allowable.

6.6.2 The surface of hot-rolled bars shall be free from visually discernible cracks, scabs, folds, fins, and inclusions. Shall any such defects be present, they must be removed.

The depth of removal, calculated from the actual dimensions of the hot-rolled bar, shall not exceed the actual dimensional tolerance of the bar. The cleared area shall be smooth and free of sharp edges. The width of the cleared area shall be no less than five times its depth. On any given cross-section, the maximum depth of removal shall not occur at more than one location. The presence of isolated minor scratches, indentations, pits, and small cracks (not exceeding 0.2 mm in depth) is allowable, provided that their depth, calculated from the actual dimensions, does not exceed half of the dimensional tolerance.

6.6.3 The surface of forged bars shall be free from visually discernible cracks, scabs, folds, and inclusions. Shall such defects be present, they must be removed. The depth of removal, calculated from the actual dimensions of the forged bar, shall not exceed 5% of the actual dimension, with a maximum removal depth of 15 mm. The cleared area shall be smooth and free of sharp edges. The width of the cleared area shall be no less than five times its depth. On any given cross-section, the maximum removal depth shall occur in no more than one location. The presence of isolated, minor scratches, indentations, and pits is allowable, provided that their dimensions do not exceed half of the specified dimensional tolerance and they do not impair the usability of the product for the purchaser.

6.6.4 At the request of the purchaser, and as stipulated in the contract, non-destructive testing methods may be employed to inspect the surface quality of hot-rolled and forged bars. The acceptance level shall be determined through negotiation between the supplier and the purchaser.

6.7 Dimensions, shape, and weight

6.7.1 Diameter and allowable deviation

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