Hardening 304 & 316 stainless steel

A. 300 series of stainless steels are known as austenitic grades and are not hardenable by heat treatment. Some hardening can be obtained by mechanical work.

A. You may get a case hardened layer with a nitriding process but the corrosion resistance of the austenitic grades as 304 will suffer. Maybe you should have to try a martensitic grade such as SAE 431 with lower corrosion resistance but hardenable.

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Ed. note: This thread quickly mushroomed, so:
1). we moved mechanical/work hardening to thread 13127;
2). we moved plating and hard-surface coatings to thread 1576; 3). we moved switching to 4xx stainless or other substrates to thread 48866; and 4). we retained this thread for nitriding & similar processes for case hardening 3xx stainless :-)

A. 304 is an austenitic stainless steel. You can't through-harden it. You might be able to nitride it, but this will probably create more problems than it is worth; nitriding would reduce the corrosion resistance.

A. Austenitic stainless steels are capable of some surface hardening, but not through-hardening treatments like quench & temper. [deleted by editor] has a process called Kolsterizing that diffuses carbon & nitrogen into the surface for increased hardness, wear resistance, etc.
I recommend you contact them for more information.

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Ed. note Apr. 2022: We always appreciate Toby's helpful and insightful replies! But this posting precipitated a race to the bottom, with more than a half-dozen vendors writing why their "unique" process was so much better than Kolsterizing or anything else. We've learned that for many reasons we can no longer post brand/sourcing recommendations (why?)

Suggesting generic processes (nitriding, plating, flame spraying) is great, and saying that proprietary processes are better than generic ones is perfectly fine too. But recommending specific sources, whether yours or someone else's just doesn't work here anymore.

A. If your cutters are thin, nitriding is the best method. We have done this before with successfully getting 65 Rc hardness up to about 0.3 mm depth. It doesn't much corrode also.

A. Hi, Usman.

We appended your heat-treatment inquiry to a thread which hopefully answers it for you: it can be annealed or it can be surface hardened, but it can't be through-hardened.

Regards,

A. Hi Guru. Rather than asking "what will be the hardness?", can you please say what you're building and what hardness you think you need and why please?.

As you'll read here, it isn't possible to heat treat SS316 to through-harden it; you can only work harden it or surface harden it. Please tell us about your application. Thanks!

Regards,

A. Hi Phil!

AISI 304 isn't the best option for getting a hardening treatment. Carburizing is NOT an option if you want to maintain its anticorrosive properties. Nitriding, however, can be done (but it's really difficult, as it's used usually on medium and high carbon steels).

Gas nitriding involves around 500 °CC, ammonia ⇦this on eBay or Amazon [affil links] injection and many hours in a closed furnace. An autoclave won't work, I think, you need a furnace with some positive pressure but no high pressures are involved in the process. You can consult manuals and Handbooks (ASM or Metal Handbook) on the subject, and I would check articles such as this: br http://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Surface_Hardening_EN.pdf (I don't know if you want to link this, Ted)

You could seek other treatments as electroless high phosphorus nickel plating to enhance surface hardness, but if you need the part to not change its size, an additional coating won't work.

So, best of luck in your project :)

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Ed. note: Thanks, Daniel! No problem with technical links except that they often quickly break, whereas this is a permanent reference site on the air since 1989. So we like to have the title, etc., so we can keep links updated. Your link has a clear title built into it, so thanks :-)

A. Search for [deleted by editor] ... it's a proprietary form of, I believe, ion nitriding. Provides a 33 micron thick case on 304 of @60 hrc.

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Ed. note: Thanks Robby. We've found that we can't post brand/sourcing suggestions (why?), but Phil can google for 'ion nitriding' and come up with this proprietary and others (although it doesn't sound like something a home metalworker like him can practically implement).

A. Hi Babak. I'm not skilled in compressor valve plates and their needs, so I don't know if this is an answer or is irrelevant, but 3xx stainless cannot be thru-hardened by heat treatment :-)

Regards,