【 Bearing Heat Treatment 】 Heat treatment process for ultra precision bearing parts

Heat treatment process for ultra precision bearing components

Ultra precision bearings, especially P2 and P4 grade bearings, require high precision, high speed (300000~400000 r/min), low friction torque, long life, wear resistance, and high dimensional stability. Mainly used for precision instruments, high-precision machine tool spindles, motor spindle bearings, etc. Generally, GCr15 and GCr15SiMn steels are selected.

1) Generally, electric slag remelting or vacuum smelting of steel is used to ensure high purity, density, and uniformity of the steel.
2) Hardness after quenching and tempering: 61~65HRC for rings and rollers, 62~66HRC for steel balls. The hardness difference of the same part shall not exceed 1HRC, and the hardness difference of the same batch of parts shall not exceed 2HRC.
3) The microstructure after quenching and tempering consists of hidden martensite, uniformly distributed small residual carbides, and a small amount of residual austenite (according to JB1255 regulations).
4) Verify that the reduction in tempering hardness is not allowed to exceed 1HRC.

1) Prepare for processing. The bearing ring blank is first subjected to normalizing and rapid annealing to refine the original structure and prepare for quenching.

2) Quenching and tempering processes. Ultra precision bearing parts have high requirements for oxidation and decarburization, so the parts should be heated in a protective atmosphere furnace or vacuum furnace. The quenching heating temperature should be set at the middle and lower limits, and the holding time should be appropriately extended to reduce residual austenite and quenching deformation. The effective wall thickness of the collar is ≤ 8mm, and it is graded in hot oil at 120-170 ℃; Effective wall thickness>8mm, cooled by hand in 30-90 ℃ quenching oil or using a rotary quenching machine.

After quenching, especially after graded quenching, ultra precision bearing parts retain a considerable amount of residual austenite. To improve dimensional stability, it is necessary to further reduce the content of residual austenite. After quenching, the parts need to be air-cooled to room temperature for 30 minutes and then subjected to -70 ℃ x (1-1.5) h cold treatment.

According to the different requirements of the parts, the tempering temperature can be appropriately increased, the insulation time can be extended, or secondary stabilization treatment can be carried out after grinding.

For P2 and P4 grade bearing parts, it is required that the residual austenite content should not exceed 5% (mass fraction). Heat treatment process for ultra precision bearing parts.