2. Metallurgical impact of absorbed nitrogen in nitrogen-enriched carbonitrided steel

As a reminder of the advantages of this type of thermochemical treatment, which is based on the same principle as case-hardening but with the addition of ammonia to supply the matrix with nitrogen, it is necessary to understand the effect of this interstitial on the iron-carbon diagram. Diffusible nitrogen, found in solid solution in austenite, will have an effect on the extent and stability of this phase. Strongly gammagenic, nitrogen will therefore lower the AC ₁ temperature (appearance of the first austenite seed on heating) and shift the eutectoid point to the left (figure 5 )