Microsoft Word 2012, Källén, M.,-Energy Efficiency Opportunities within the Heat Treatment Industry

2.2.3  Nitriding and Nitrocarburizing 

Nitro-processes are performed to increase the fatigue strength and the load-bearing capacity 

of the steel. Nitriding is a process where nitrogen is added to the surface of the steel from an 

atmosphere containing nitrogen. The process is usually carried out at 500-550°C. Ammonia, 

diluted by hydrogen or nitrogen gas, is usually the nitrogen donating medium. The 

atmosphere is completely free from oxygen to avoid the risk of explosion. The concentration 

of ammonium is highest in the beginning of the process and is then decreased. The nitriding 

continues until a desirable nitride depth is achieved. The ammonium gas is then removed from 

the oven and the steel is washed in nitrogen gas. The cooling is also usually carried out in 

nitrogen gas. [1] 

Nitrocarburizing is a nitriding process where both nitrogen and carbon are transferred to the 

surface layer of the steel. The temperature is slightly higher than for nitriding, usually 550-

580°C. A variety of gases is used as carbon donator, for example carbon monoxide and 

carbon dioxide. Nitrocarburizing is easily mixed up with carbonitriding, since both processes 

aim at adding carbon and nitrogen to the steel. However, nitrocarburizing is carried out at a 

much lower temperature than carbonitriding. [1]