For the reason you mentioned I always use the nitriding process and not carbo-nitriding. Why you mentioned the ammonia furnace treatment in that context is not clear to me. Where would the carbon come from in ammonia atmosphere (=NH3)?
Compared to the nitriding process, carbo-nitriding is not true to size, so can not be done without subsequent grinding. The nitrided journals will only need a bit of polishing and are ready to fit.
Comes from not checking my post properly before I send then and changing my train of thought on the fly ( somthing about playing on the net when I should really be in bed )
I am nearing the limit of my Ferrous metallurgical knowledge as I was principally in tertiary metallurgy and non ferrous foundry to boot so did not do much with steel after I left uni.
As for the formation of nitrides & complex nitrogen phases at the surface , this is something that I was totally unaware of and would have thought both the concentrations of nitrogen and temperatures were too low for the formation of such phases in sufficient quantaties to alter the bulk properties if at all.
I no longer have access to TTT curves so could not verify how near the tempering temperatures nitriding would be done and what affect if any this heating would have on the microstructure of the particular alloy. I was always led to believe that gas nitriding was done very close to the tempering temperature to reduce the heating time ( & costs )
A couple more things that I have learned for which I thank you.
The principal object of the post was to distinguish between the two processes which just sound like different names for the same thing and as we have established are totally different and clarify which you were talking about.
As stated I always recommend nitriding and have had a couple of locals looking to shed my blood after they Carbo ritrided their cranks which failed very quickly.
