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

2.2.2  Case hardening and Carbonitriding 

Case hardening is a hardening process which is carried out in a carburizing atmosphere. It is 

usually performed at 850-950°C. The steel will get a surface layer with higher carbon content 

than the core of the steel object. This will result in a very hard surface and a much softer and 

tougher core. The hard surface is obtained when martensite is formed from austenite by a fast 

cooling process. [1] 

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Carbonitriding is a form of case-hardening where both carbon and nitrogen are added to the 

steel. This is achieved by performing the case hardening in an atmosphere containing 

ammonia. The presence of nitrogen increases the hardenability of the steel, and makes it 

possible to case-harden also low-alloy steel. [1]