Difference between carburizing and nitriding

What is carburizing?

Carburizing is a heat treatment process that diffuses when the metal is heated in the presence of carbon-bearing material, such as charcoal or carbon monoxide, in order to make the metal harder.

Example - Precision gears

What is Nitriding?

Nitriding is a heat treatment process that diffuses nitrogen into a surface of the metal to create a case-hard surface are most commonly used on low-carbon, low-alloy steels, but also in medium and high-carbon steels, titanium, aluminium and molybdenum.

Example: Crankshafts

Main difference : 

Carbon is made to diffuse through the metal surfaces in carburizing whereas in nitriding nitrogen is made to diffuse.

Let us have a deep insight into the comparison and difference between carburizing and nitriding. 

Difference : 

  • Nitriding does not cause smash or rift or any change in metal properties because it does not need to sprinkle to get surface hardening and also it doesn't need to high temperature as carburizing.
  • Carburizing and nitriding both are heat-treatment processes and used for surface hardening of the low carbon steels and also medium and high carbon steel.
  • Carbon is diffused on to the surface of the metal in carburizing whereas nitrogen is diffused in the nitriding process. 
  • Carburizing has done at a very high temperature and carbonaceous environment while nitriding has done at low temperature and in a nitrogen environment. 
  • Nitriding produces harder and stronger cases as compared to carburising.

For the graphically view Hardness versus Case Depth HRc 60 is a hardness measurement on the Rockwell C scale, typically this value is the benchmark for a carburized steel, remember when started out in heat treatment you would sometimes use ‘hardened metal files’ and rub these across a surface of the carburized steel to check if the steel had sufficient hardness (file would polish) or if the surface was poorly treated and had low surface hardness, the file would scratch in to the surface of the steel.

Carburizing Vs Nitriding

When considered in gears :

Carburized gears feature a much deeper, hardened layer that gradually decreases its hardness to the core hardness. This structure provides superior surface contact fatigue properties and ductility/impact resistance and strength of the core. Moreover, like a needle roller bearing surface in the planet gears, sufficient case depth obtained during the carburizing process is required.

Nitride gears can have a very hard and brittle white layer on the surface. It is not removed it can be prone to flaking and cracking leading to heavy surface fracture and gear failureThe hardened case depth is considerably thinner than in similar carburized gears and transitions immediately behind the case to the core hardness.

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