Nitriding

The purpose of nitriding is to increase the surface hardness of the steel and improve its wearing properties. This treatment takes place in a medium (gas or salt) which gives off nitrogen. In nitriding, nitrogen diffuses into the steel and forms hard, wearresistant nitrides. This results in an intermetallic surface layer with good wearing and frictional properties.

Nitriding is done in gas at about 510oC (950oF). The process therefore requires steels that are resistant to tempering in order that the core strength is not reduced.

 

Nitriding Process

Ammonia is introduced in a controlled atmosphere chamber at elevated temperatures.

NH3 breaks down on steel surface containing nitride forming elements.

Diffusion zone forms.

Compound(“white”) layer can form on the surface due to bcc-Fe forming stable equilibria with nitrogen gas.

 
 
 
 
 

Phases in the Fe-N System

 
 

 

 

 

 

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Advantages of KN Controlled Gas Nitriding

 

• White layer thickness and phase control
• Prevention of grain boundry nitrides (nitride network) 
• Depth control
• Surface hardness control
• No distortion
• Process repeatability
 
 

Nitriding

8550
4140
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