TTI Group Heat Treatment & Surface Treatment
Surface Engineering and Heat Treatment Specialists

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Head Office: TTI Group Ltd, 39-43 Bilton Way, Luton, Bedfordshire, LU1 1UU, UK

Tel: 01582 544600  Fax: 01582 488394



Carburising & Carbonitriding

These processes are useful if there is a requirement for a hard, wear resistant surface, overlying a much softer and tougher core. A good example for its application is a gear wheel. The surface of the teeth needs to be extremely hard so that they can withstand constant metal-to-metal contact, without undue wear. The underlying material needs to be tough so that the teeth can tolerate occasional impact loads, without the risk of fracture.

Hardness and toughness are normally incompatible in a steel of a given composition and microstructure. To make a component from a low carbon steel and introduce additional carbon (and/or nitrogen) into the surface to a controlled depth from some external source has to be done with the component at a high temperature.

The surface is then capable of being hardened, whilst the core remains relatively soft and tough. Examples of the processes which use this approach are:
  • Carburising;
  • Carbonitriding;
  • Nitriding;
  • Nitrocarburising

Carbonitriding is a high temperature heat treatment designed to produce a hard wear resistant surface.

Carburising and Carbonitriding are carried out at Blackburn, Cheltenham, Letchworth, Luton and Tipton Plants. Please see individual Plant pages for contact details.

Carburising

Carburising is also called Case Hardening. Case hardening, properly known as carbon case hardening, is used to give a hard, wear and indentation resisting surface to mild and low alloy steels, up to depths of 4-5 mm. This is achieved by diffusion of carbon into the surface of the steel. At the same time the core of the steel is usually strengthened, but left tough. Being one of the most common heat treatment processes used in the world, case hardening is commonly applied to gears, machinery, automotive and aerospace applications and many others.

Carburising is carried out in the temperature range 800 - 960ºC where carbon is diffused into the steel surface. The core of the steel is strengthened by rapidly quenching from these temperatures and the resulting hardness is dependant on the quench rate and also the steel. It is recommended that Carburised parts are tempered at low temperatures for optimum toughness.

Changes in size or shape can occur to components, however certain components can be Press Quenched to minimize this.
 
Steels
Carburising is an excellent process to provide a hard, wear resistant surface to inexpensive steels such as low or medium carbon steels. Mild steels can also be treated but will not generate good core strength.

CarboNitriding

Under the heading of Case Hardening is also included carbonitriding, which is used to give a hard case onto the cheapest steels which are often not capable of being case hardened because of their chemical composition. The carbonitriding process is applied to low carbon and mild steels and results in less distortion than traditional carburising techniques.

Carburising & Carbonitriding


Available at:

BLACKBURN

CHELTENHAM

LETCHWORTH

TELFORD

TIPTON


Commonly

Treated

Materials


080M15

665M17

832M13

AISI1020

TAISI8620

17 NiCrMo6



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