4. Justification of thermochemical treatments

Mechanical parts need to be resistant to the various stresses to which they are subjected. These stresses are mainly mechanical (static or dynamic mechanical constraints) and environmental (ambient reactive environment), leading to various modes of degradation, either massive or superficial.

• Damage resulting from localized surface stresses can be avoided or slowed down by modifying surface properties, in particular through surface treatments and coatings.

• Damage resulting from deep stresses will require sufficiently high mechanical properties at the depths concerned.

  However, even for deep stresses, initiation starts close to the surface, and surface-hardening solutions, combined with core reinforcements, are often a high-performance choice.

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