Description of heat treatment process for medium load gears and carburized gears

The relevant descriptions of the heat treatment process for medium-duty gears and carburized gears are as follows, for reference.

XNUMX. Medium load gear (medium carbon steel) heat treatment (surface hardening)

Suitable for 35～55, 40Cr, 35CrMn, 35CrMo, 42SiMn and other materialsgear.

1. Normalizing (or complete annealing):

Refine the grain, adjust the hardness, heat to Ac3+30～50℃, air cooling, fine pearlite+ (a small amount of ferrite).

2. Quenched and tempered heat treatment:

使心部具有良好强韧性，加热至Ac3+30～50℃后淬火+500～600℃高温回火，回火索氏体。

3. Surface induction hardening (surface flame hardening):

Improve the surface hardness, the surface is heated to Ac3+30～50℃, the core is not heated.Martensite is obtained on the surface after quenching, the transition layer of martensite + S back + retained austenite, tempered sorbite in the core

4. Low temperature tempering:

Eliminate quenching stress, low temperature 200℃, M→M times

20. Carburized gear: Material: 20CrMnTi, 30Cr, XNUMXCrMnTiA, etc.Service occasions: high-speed and heavy-duty (automobile gear)

Process:

1. Normalizing:

The purpose is to refine the crystal grains; adjust the hardness to facilitate cutting, heat to Ac3+30～50℃, air cooling, to obtain fine pearlite+ (a small amount of ferrite).

2. Carburizing:

Increase the surface carbon content, and keep it at 920～930℃ for 3～9h.

3. Quenching after carburizing:

Obtain martensite, improve surface hardness, and quench directly or once.Ideal organization: surface: contact needle M+Ar (small amount) + carbide, heart: low carbon M+F (small amount).

4. Tempering:

Eliminate quenching stress, low temperature 200℃, M→M times

The carburized gear should meet the following requirements after heat treatment:

1、表面层硬度HRC58～63，心部HRC31～45

2. The surface and core should have fine grain structure

3. The surface metallographic structure should be fine needle-like or cryptocrystalline martensite structure, along the grain boundary

Net carbides are not allowed, only a small amount of granular carbides and retained austenite are allowed

4. There should be enough transition layer between the surface and the heart

5. Heart tissue after heat treatment:

Alloy steel, low carbon martensite or low carbon martensite + ferrite;

Carbon steel, pearlite + ferrite

6. Minimize decarburization and deformation

7. In addition to requiring high toughness, the heart must also have high strength.