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Nitriding/QPQ Assistance
Q. Apologies if this is answered already on this site, but could anyone point me in the direction of a reliable source to understand the difference between carbonitriding, nitrocarburizing, the various Nitriding processes (salt-bath, gas, plasma) and where QPQ fits into this? I'm trying to understand if/how QPQ is done after gas-based nitriding or is it usually needed after salt-bath nitriding only?
The salt-bath nomenclature is also a bit confusing for me, as it seems that names are used interchangeably at times (like Tufftride and Tenifer and Melonite and Melonite QPQ); I'm unsure if they are describing the same process, but with a different marketing title or if they are completely different processes altogether. It seems some of the salt-bath processes are being grandfathered due to their use of cyanide, but I'm not sure if that means the new conforming versions are retaining their original name or if they are given new marketing names.
Sorry for the long post; I don't want to rely on ChatGPT/AI for learning about this and am hoping some folks in the industry might be able to help. Many thanks in advance for any advice/direction!
Student - Cleveland Ohio
August 4, 2025
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A. Hi. We have a paper in our on-line library on the Kolene QPQ salt bath nitriding process, which explains that QPQ stands for quench-polish-quench, the steps involved, the reason for them, and the purported advantages.
As for the rest of the names associated with salt bath nitriding like Tufftride, Tenifer, and Melonite, they are all exactly the same thing according to HEF Deferrit USA who now owns them all.
The general idea is that salt bath, gas, or plasma nitriding are all intended to achieve roughly the same thing. And when we say that one is better than the other for this or that, the problem becomes that every process usually develops proprietary tweaks over the years both by the vendor selling the technology and little trade secrets developed by the shops doing the process. This makes it hard to say conclusively that salt bath, gas, or plasma nitriding will be superior for a particular application. The best approach is probably to read the advocacy literature for each, for example --
• gaseous: www.paulo.com/resources/salt-bath-nitriding-process-safer-alternative/
• plasma: www.ahtcorp.com/services/nitriding-and-nitrocarburizing/ion-plasma-nitriding/
Naturally each makes claims for the advantages of their technology, and each weakens the claims of the others, but you'll end up with a good understanding.
You can also search our site for many real-world discussions of problems, successes and difficulties with those technologies. Sometimes reading what real people are actually encountering can trump sales pap.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
(Ted is available for instant or longterm help)
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