case hardening
what is case hardening?
Case hardening is a thermo-chemical process. Within the framework of this process, the surface layer of components is enriched with carbon (carburization), in order to improve the mechanical properties of the component surface layer.
the process
As a rule, case hardening comprises three working steps. In the first step, the workpieces are exposed to a carbon rich environment at a temperature of 800 to 1,050 °C. In the second step, the quenching takes place either directly from the application temperature or after intermediate cooling and reheating to a material-specific hardening temperature. The third step, the tempering treatment serves essentially to relieve the highest stresses in the material structure and to reduce sensitivity to grinding cracks.
in short
workpiece before
Case hardening steel (C ≤ 0.25 %)
- easy to machine
- easy to weld
- outstanding toughness
workpiece after
Core zone (C ≤ 0.25 %)
- tough and ductile
- enhanced service properties
- (toughness and, if applicable, strength)
Surface layer (C = 0.70…0.90 %)
- hard and wear resistant
- improved fatigue strength under
- vibration stress
fields of application
Case Hardening
results in a very hard case of the component: specifically, this is useful in
the case hardening of gears and similar components which are subject to a great
deal of wear in hostile environments. This heat treatment process is especially
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.
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. 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.
Steels
suitable for case hardening are unalloyed or alloyed steels with a carbon
content below approx. 0.25%.
Partial
case hardening is possible, thanks to suitable insulation techniques.
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