Termochemistry/Nitriding

Thanks to its experience of over 50 years in the field of thermochemical treatments, HEF Group is the world leader in the field of nitrocarburizing in ionic liquid medium.

The various treatments patented and commercialized by the HEF group under the designations ARCOR®, TENIFER®, TUFFTRIDE®, Melonite®, NUTRIDE® and QPQ® concentrated under the name CLIN: Ionic Liquid Controlled Nitrocarburizing (nitrocarburizing in ionic liquid). Treatments CLIN and associated industrial facilities are easily adapted to various environmental and technical constraints, and their applications are constantly developing.

These treatments are mainly applied in iron alloys (steel, cast iron, stainless steel, etc.) and are between 500 and 630 ° C.

The goal of treatment is CLIN, from a heterogeneous surface reaction, to provide solid metal alloy nitrogen and carbon contained in the molten salt.
After the addition of nitrogen to the steel, two distinct phases are obtained:

  • A layer of iron nitrides (mainly Ɛ-Epsilon type, but also Υ’-type gamma prime) and nitrides of elements alloyed called composite layer, which has the particularity of being superficially porous
  • A diffusion zone below the composite layer, in which nitrogen is present in solid form between the iron atoms (or alloying elements).

Thus is obtained from the surface, a gradient of hardness and compressive forces that allow particularly improved resistance to wear and fatigue. The thicknesses of the composite layers and diffusion depth depend on the nature of the substrate and CLIN process performed, however, these can be from 0 to 30 .mu.m for a composite layer, and reach a few tenths of millimeters for diffusion.

Furthermore, in order to provide excellent corrosion resistance (in atmospheric, alkaline or acidic medium) is subsequently performed one passivation step in an oxidizing bath, creating oxides Fe 3 0 4 (magnetite) embedded in the layer porous, and a final impregnating anticorrosive organic type which will fill the porosity while providing a dry to the touch.

The corrosion resistance can exceed 700 hours in saline fog for simple parts and can usually reach 400 hours in salt spray for more complex parts.
In the case of particular requirements of roughness (for example friction against polymers, elastomers), polishing steps are required after treatment. Then being QP or QPQ type processes.