Carburizing of Gears

Carburizing is a process of heat treatment where the concentration of carbon on the surface of a gear is is increased by a process of inward diffusion. This is done at temperatures between 850 -950°C (1560 and 1740°F). To drive the diffusion flux, heat treatment is conducted in an environment where carbon's chemical potential is more than as compared to steel. The environment may be either solid or gaseous. The surface carbon concentration after increase is subsequently quenched. This results in transformation of the surface into a hard martensite. This can be followed by other types of heat treatments.

Types of Carburizing
There are following methods for carburizing

• Gas carburizing
• Vacuum carburizing
• Plasma carburizing
• Salt bath carburizing
• Pack carburizing
• Low Pressure Carburising

Vacuum Carburizing
Gears are very well suited vacuum carburizing process. Advantages include minimal distortion and an uniform case depth, that includes gear root to the pitch ratios. Traditionally chemicals for vacuum carburizing of gears were selected from a saturated aliphatic hydrocarbons like methane and propane. Recent developments have made it possible to use unsaturated aliphatic hydrocarbons. Vacuum carburizing processes are used with or without plasma for application in the gear industry.


The striking features of a Vacuum carburizing Gear are the following:

• Minimal distortion as result of gas quenching.
• Elimination of microstructure intergranular oxidation (IGO)
• Improved fatigue life
• Bright, clean parts after processing.

Low Pressure Carburizing (LPC)
Low Pressure Carburizing (LPC)is a highly advanced technology. It gives the Gear design engineer another alternative for improving case depth uniformity. LPC is a combined method of pure carburisation and pure diffusion. Advantages include

• Enhanced Mechanical Properties
• Dimensional Control
• Cost control
• Environmentally sustainable
• Improved cleanliness of products
• Reduction in manufacturing steps