Controlled Gas Nitriding Process and Its Benefits to Low Carbon Steel

04 June 2019

Atmospheric control is a powerful tool in a heat treatment engineer’s metal hardening armoury. For example, by adding gaseous nitrogen to a furnace, the gas nitride hardening effect is initiated. This process sees the gas come into contact with a heated low carbon workpiece. As the surface metal and nitrogen brush against one another, the gas diffuses. The result of this gaseous interplay is a stronger, nitride hardened low carbon component.

The Benefits of the Gas Nitriding Process

Well, there’s one immediate upshot, which we’ll reveal right now. Without further delay, because the gaseous ammonia is diffused, there’s no quenching operation required after the process completes. That means there can’t be any quench-induced dimensional changes or material distortions. A scuff and corrosion resistant casing are applied, but there’s no workpiece warping occurring during the hardening procedure. Better yet, the material properties underneath the hardened casing remain fundamentally unaltered.

Viewing the Process Advantages from the Other End

In-process, the benefits are a little harder to define. The nitrogen gas, which is usually applied as an ammonia base (NH3), produces a thin, abrasion-proof coating. Underneath that coating, the alloy workpiece remains unaltered. Like any other mild steel component, it remains malleable and workable. Coming out of the atmospherically sealed furnace, though, more benefits are witnessed. The tough outer coating is there, yet the workpiece is inexpensive and easy to source. The process repeats in no time at all, probably because there’s no additional quenching work to perform. Better yet, the gas output can be controlled with the twist of a valve. That’s a massive plus in the pros column. It’s not always so easy to control furnace heat. Thermal loads require pre-heat phases and cool down periods. That part of the process is obviously harder to master. With convection currents and a sealed furnace, gas diffusion work is that much simpler to manage.

Finally, there are no unidentifiable surface residues to clean off when gas nitriding is the chosen surface hardening process. The nitrogen diffuses cleanly, the nitride hardening effect is triggered, and the job comes to a close. Indeed, this heat treatment approach has all the hallmarks of a turnkey alloy tempering procedure. It starts inside a sealed furnace, absorbs its nitrogen load, yet stays malleable and machinable. Then, right at the end, as the workpiece exits the furnace, the job is done. There’s no quenching phase, which would alter the geometry of the part and cause workpiece distortion. With the cooled part shuttled away to a storage room, clean and without any in-process residue, the next job commences.

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