toughening process design of precision bearing ring made of GCr15 steel

(1) Failure analysis of precision bearings, precision bearings, when working, withstand up to 300 ~ 500 MPa of alternating contact pressure and friction, and withstand media corrosion. Its failure characteristics are: loss of precision due to excessive wear or stress relaxation; pitting on the surface of contact fatigue; brittle fracture due to poor carbide morphology and poor distribution or poor toughness of raw materials. Therefore, the precision bearing parts have high requirements for the original structure of the billet, and the heat treatment should have high strength, good toughness, wear resistance, corrosion resistance and dimensional stability. The bearings in the special environment need corrosion resistance, high temperature resistance, and no magnetism.

(2) the manufacturing process of precision bearing ring is made of blank forging, spheroidizing, mechanical cutting, quenching, cold treatment, low temperature tempering, coarse grinding, aging, finishing, and aging.

(3) in order to improve the quality of the billet and lay a good foundation for the final heat treatment, the preparatory heat treatment process of the precision bearing ring is laid on the blank by forging and rolling waste heat quenching and high temperature tempering, in order to refine the carbide and grain at the same time.

(4) the final heat treatment of the precision bearing ring is designed to make the bearing ring strong and toughening effect. Martensite classification quenching, tempering and cold treatment, as well as the process of aging treatment after coarse grinding and fine grinding are proposed.
The process is as follows:
1) grade quenching: in the fully deoxy BaCl2 and NaCl each 50% (mass fraction) of the salt bath furnace, at 840~850 C heating after heat transfer into 200 c hot oil to keep 3min after the oil cooling.
2) tempering: air cooling is maintained after 2.5~3.5h in the 215~ 225 degree salt bath.
3) Cold treatment: in the medium of liquid carbon dioxide + alcohol, about - 78 65507
4) aging: in a fan incubator, maintain 5h at 135 degrees centigrade and turn to fine grinding after air cooling to room temperature.
5) aging after fine grinding: 130~140 10h, after air cooling.

(5) the measured hardness is 61HRC, the average carbide particles are about 0.5 m, the retained austenite (volume fraction) is about 2.8%, and the size is stable (the deformation is less than 1 mu m).

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