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Carburizing, Carbonitriding Gear Heat Treatment Methods

Steel grade Item Gear type Heat treatment process



















Most gears that have been carburized (or carbonitriding) by gas or liquid


Carburizing (920-940℃) or carbonitriding (840-860℃) → furnace pre-cooling, soaking (830-850℃), (carbonitriding is not pre-cooling) → direct quenching (oil quenching or hot oil martensite grading quenching) → tempering (180℃,2h)





1) After direct quenching, the gear whose distortion does not meet the requirements needs to be quenched by pressing bed or sleeve bar

2) Gears that need to be machined after carburizing

3) solid carburizing gear


Carburizing or carbonitriding → cooling → reheating (850-870℃) → quenching (oil quenching or hot oil martensite grading quenching) → tempering










High precision requirements (7) gear

The gear is roughed before carburizing.After carburizing, it is cooled down at a slower cooling rate, and the semi-finishing of gear is carried out.The diathermic tooth and the part near the tooth root are quenched by high frequency or medium frequency induction heating device. After tempering, the tooth shape is finished (honing or grinding) and the inner hole of the spline is finished by pushing knife





Carburized gear

Direct quenching after carburizing, such as coarse grain, it is appropriate to use the No. 2 heat treatment process for processing
















Carburized gear

Carburizing (900-920℃) → cooling → reheating (12CrNi3A, 20CrNi3A, 12Cr2Ni4A, 20Cr2Ni4A: [800±10℃); 18Cr2Ni4WA:850±10℃) → quenching (oil or (200±30℃) alkali tank, after holding 5-10min, air cooling) → cold treatment (-70 ~ -80℃×1.5-2h) → tempering




Gears that need to be machined after carburizing

Carburizing → cooling → high temperature tempering (650±10℃) × 5.5 ~ 7.5h, air cooling, 18Cr2Ni4WA should be with the furnace cooling below 350℃ air cooling → reheating → quenching → tempering










Generally, after quenching, the core of the gear is too high hardness

Quenching can be carried out according to the following specifications:

18Cr2Ni4WA: 850±10℃ after insulation, quickly put into the 280-300℃ alkali tank, keep 12-20min, into the 560-580℃ saltsalt bath for 30-50min oil cooling

12CrNi3A: After heat preservation at 820-850℃, it was kept in an alkali tank at 230±50℃ for 8-12min in oil cooling




Carbonitriding gear

Carbonitriding (830-850℃) → direct quenching (oil or alkali tank, martensite grading quenching, 18Cr2Ni4WA available air quenching) → cold treatment → tempering



Gears that need to be machined after carbonitriding


Carbonitriding → cooling → quenching → tempering

① Too much austenite or too high core hardness in the infiltration layer can reduce the quenching temperature to 760℃, while the core hardness is too low and the amount of ferrite is too much, and the quenching temperature can be increased to 850℃.

② The hardness after tempering should not be higher than 35HRC.If the hardness of individual parts is high, it can be tempered once again at 680-700℃.

The above process curve is summarized based on the actual process of many customers’ products and the reference heat treatment design manual, which can be used for the reference of the majority of industrial furnace enthusiasts and users.More heat treatment equipment design information, welcome to inquire!

Editing by Francis Lee

Copyright: RQ Furnace

Learn More :

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