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Please allow me to respond to a couple of points.
1. You are correct. You did not refer to nitrocarburizing in your article. It was my suggestion that the salt-bath nitrided specimen is likely to be salt-bath nitrocarburized because the phrase “salt bath nitriding” almost always means “salt bath nitrocarburizing.” But, if it was a true liquid nitriding process, my comments are irrelevant.
2. Regarding carbon, if the specimen has been nitrocarburized, the added interstitial carbon would be detected only by surface analysis. We would expect a maximum of 3% by weight within the compound layer, down to about 1% at 20-25 µm (probably less here because the layer is uncharacteristically thin. 1250x?).
3. If by high hardness you mean >58 HRC, I agree regarding the required alloying elements. However, again – within the compound layer – a hardness of 55-58 HRC (by conversion from HK or HV) may be obtained in unalloyed steels. But 100g loads are far too heavy to measure such a thin layer accurately. And some hardening does take place within the diffusion zone below the compound layer, to a much lesser degree, as I believe Fig. 2 in the article shows down to about 0.3mm. Also, in my opinion, in addition to the hardness profile in Fig. 2, the nitride needles shown in Fig. 1 are evidence that a nitrogen diffusion zone is present, though the caption says there is none. Perhaps it means “none visible.”
4. Finally, and most importantly, I repeat and agree that my comments are of minor significance to the subject of the article. Please forgive me if it seems I am making a “mountain out of a mole hill.” The entire motivation for any of my comments is the assumption that the salt-bath nitrided sample is actually salt-bath nitrocarburized, because salt-bath nitrocarburizing processes are routinely referred to as salt-bath nitriding processes in industry. If it is a salt-bath nitrocarburized specimen, I felt it important to point out that the photo and some of the statements are not necessarily representative of salt-bath nitrocarburizing.
Thanks so much for your willingness to “banter” on this subject and certainly for your patience.