The heat treatment process of carburized workpiece

I. direct quenching process after carburizing

Direct quenching after carburizing can only be used when high surface hardness is required and other mechanical functions are irrelevant.

For some important parts (the gears in the gearbox), the following measures must be taken:

1. Adopt fine grain steel (such as 18CrMnTi,18CrMnMo, etc.).

2. The application of gas carburizing takes less time to reduce the possibility of grain growth.

3. Precooling is added when quenching. Even if the workpiece from the carburizing temperature out, pre-cooling to 780 ~ 800℃, then quenching. The internal stress is reduced and the strength is improved accordingly.

4. The application of cold treatment can change the residual austenite and increase the hardness. In all cases, the part must be tempered at low temperature at 160 ~ 180℃ to eliminate internal stress. The surface hardness reaches HRC58 ~ 62, and the central hardness is generally between HRC25 ~ 35.

Second, after carburizing heating quenching process

If the organization and mechanical requirements of the workpiece is higher, it should be carburized now in the air cooling, and then heated to 850 ~ 900 ℃(quenching temperature should be determined with the material) quenching. In general, this quenching temperature exceeds the critical temperature between the surface and the center, so recrystallization refinement occurs during quenching heating. However, the high carbon surface carburized layer exceeded the Acm temperature. After quenching, the residual austenitic volume was larger and the hardness decreased. However, the original network cementite or bulk cementite is heated to this temperature and disappeared.

Double heat treatment after carburizing

Double heat treatment after carburizing is used to meet the extremely high functional requirements of parts. The method is as follows: the first quenching is done after carburizing and then heated to 850 ~ 900 ℃. The purpose is to refine the core tissue and clear the mesh or block carburizing of the surface layer. Since it does not need to reach the final hardness, it can be cooled in oil or air.

After this treatment, the core grain is refined. The parts are then heated to the normal quenching temperature of high carbon steel (780 ~ 800℃) for a second quenching. In this way, the needle-like martensite embedded with excess cementite can ensure that the workpiece has high hardness and wear resistance.