Nc Nitrocarburizing
Nitrocarburizing · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Gas nitrocarburize · compound layer ≤0.02 mm” states a nitrocarburizing requirement.
What controls
Diffusion treatment at moderate temperature in which nitrogen and carbon enter simultaneously, forming a surface compound layer with a diffusion zone beneath it. It provides wear and galling resistance, improves fatigue performance and, with a post-oxidation treatment, some corrosion resistance. Unlike classic nitriding, it works on unalloyed steels, and it causes very little distortion. What the drawing usually specifies is the compound layer thickness and surface hardness.
How to verify
Metallography on a witness coupon to measure compound layer thickness and diffusion depth, and microhardness for surface hardness, with a low load because the layer is so thin. If the drawing requires corrosion resistance after oxidation, that is certified by the corresponding test, not with the hardness tester. The heat treatment certificate must identify the cycle and the thicknesses obtained.
Workshop guideline values
- General
- Compound layers on the order of 10–20 µm on ordinary wear parts.
- Accuracy
- Compound layers controlled below 20 µm with specified surface hardness.
- High precision
- Thicknesses certified per load by metallography, with control of the diffusion zone.
Guidance only: the drawing's value always wins.
Common mistakes when interpreting it
- Confusing it with carburizing: here the layer is measured in microns and does not tolerate subsequent grinding.
- Specifying only surface hardness without a compound layer limit, which is what usually fails.
- Aggressively machining or polishing after treatment and ending up with no layer.
How to get it in the workshop / if it comes out of tolerance
It is an economical alternative when a hard surface without distortion is needed and the steel is not a nitriding grade. It is applied to the finished part. The layer is very thin, so any subsequent rework compromises it; if the drawing allows polishing, keep it light. The finish usually comes out dark or black when post-oxidized, and that is part of the result, not a defect.
Compound layer above the maximum: the cycle was too long or the potential too high; it is adjusted in the treatment. Flaking of the layer: compound layer too thick or surface contaminated before treatment. Low surface hardness: first check the measurement method, then that the material and cycle were appropriate. If the part has to be machined afterward, the layer is lost and the treatment is wasted.
Related symbols
Other symbols in Heat treatment
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