powder coating yoyos is iffy, it can induce vibe pretty easily and it’s a very common problem among powder coated yoyos the last ~25 years. It can be done well, but tbh most coaters just don’t care that much and don’t usually deal with things that require precision balance.. most of the pc finishes also just feel icky on a yoyo.
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AFAIK, most stainless steels used for yoyos is austenitic, though this is speculative as the grade is rarely listed. Many weight rings are 316 and some specify the grade, like the Bowl 303 uses a 303 SS.
But this is where my lack of post-grad education starts to show - I don’t know WHY you can’t use a typical heat-treat process for austenitic stainless steels. From what I’ve read, it’s because the crystal structure, FCC, is extremely stable at all temps due to the high Ni and Cr content, but I don’t understand the mechanism of why this is.
Looking at the TTT diagram, it seems like it should be possible with a fast enough quench to transform the austenite (soft) into martensite (hard):
(AISI 316 TTT)
But apparently not!
And I’ve read conflicting claims on cryo-treating 316. Theoretically, a cold enough cryo treat could transform austenite into martensite, but I guess the darn FCC won’t let that happen.
Your other options would be to work harden strain strength via cold-working it, which would likely cause severe vibe, or some sort of nitriding process.
I’m guessing ALL stainless steel yoyos are made out of austenitic 300-series SS. You’d need a martensitic grade (400 series) to make something hardenable.
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While a good jumping off point, you can’t only look at carbon content to determine hardenability.
I work for an automotive supplier, specifically with press-hardenable steels, mostly 22MnB5 (trade name Usibor 1500). It has a C content of 0.19-0.25 wt% and it’s quite easy to hit 500+ HV10 (52+ HRC). Granted, that’s a bit low for your average high-C knife, but it’s also half the amount of carbon compared to a common knife steel like 5150.
What’s funny is I’m also diagnosed austenitic. Ba dum tss.
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I know. This is why I also didn’t say it’s the only thing to look at. And that there are exceptions all over the place.