Ferrous Materials and Non-Ferrous Metals and Alloys 1 introduction

(4) Carbonitriding:

 It is the technique of producing hard case by addition of nitrogen

and ammonia on the surface of the steel with the help of gases. Ammonia, carbon monoxide

and hydrocarbons are used for carbonitriding. Carbonitriding is carried out at a

temperature of 780°C to 875°C with 840°C being most common for 6 to 9 hours. The

process is carried out in a furnace with the supply of carrier gas (hydrocarbon, ammonia

and carbon monoxide) under positive pressure to check and prevent air infiltration.

Thus, making the process control easier.

At the furnace temperature the added ammonia breaks up to provide nitrogen on

the surface of the steel.

Nitrogen in the surface layer of steel components increases hardenability and permits

hardening by oil quench (instead of water quench). Thus, chances of distortion and

cracking are eliminated. The portion of steel components which is not to be carbonitrided

can be protected by a layer of copper.