This involves the introduction and diffusion of carbon into the surface layers of the steel, after which the low carbon steel component now possesses a high carbon steel surface
On subsequent hardening of the component, this surface responds to give an exceptionally high level of hardness and wear resistance, whilst the low carbon core remains relatively unaffected and maintains its original toughness.
The depth of the hardened surface is measured by case depth which is defined in one of two ways
- Effective Case Depth – measured to where the hardness decreases below a given value
- Total Case Depth- measured to the boundary with the uncarburised core material
Holts have the capability to carburise components ranging in weight from a few grams up to a number of tonnes and in sizes up to 2.7m in length or up to 1.5m in diameter.
Carburising has a limited window of processability.
A very high threshold temperature before carbon absorption and diffusion will commence and a limit on the upper temperature range because of the risk of softening and sagging of the work piece.
A narrow band of carbon concentration, too little and the diffusion into the steel stall, too much and it precipitates as iron carbides destroying the sought after mechanical properties.
The combination of carburising and hardening changes the microscopic structure and therefore size of the surface of the steel. In effect the surface grows which can lead to distortion particularly in deep case depths or when thin components are carburised
Holts accurately control the type and depth of case, using computer modelling and in process control techniques to account for the variation in processing different steel alloys or casts and so meet the most exacting specifications.
We regularly process case depths from just 0.25 on thin sections up to 9 mms effective case depth on large gears.