While I don’t get exactly why you would do it, I was wondering if the type of steel typically used in full-stainless yoyos would technically work for hardening via high-temperature and oil quenching? Again I don’t think it would work well, this is just a question of pure curiosity.
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Post-thought: would walking the dog on said yoyo subject it to case-hardening?
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I don’t see why it wouldn’t, though I’d imagine it would make it more brittle.
As for the WTD? Literally no idea lol. I suppose the friction generated heat would make some of rhe material harder, but this is far beyond my knowledge tbh, I’m a humble mechanic
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Yeah I can’t think of any reason why to do it, but like I think there’s enough carbon for quench hardening.
Don’t tempt me to destroy my new oasis for science, it hasn’t even shipped yet lol
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That would give you extra reason to support Dressel and buy another lol (trust me, you’ll like it. I’m not a huge fan of that shape or type of yoyo but it won me over nonetheless)
Kind of a complicated question, but a good one.
I haven’t looked, but I’m assuming most stainless being used is either 304 or 316. That would mean that they can be case hardened with nitriding, but they can’t be through hardened and they don’t heat treat because they’re austenitic.
If they use any of the 400 series stainless it’d work though, they’re just not as common for general applications. You can heat/quench/anneal to get a wide variety of hardness. I’d be VERY weary of doing it to a full yoyo though, major deformation is going to be a serious risk given how thin the walls get.
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I would expect any thermal/quench hardening method to cause warping in most cases (unless you hold it in a jig)
many metals can be work hardened, including some aluminum alloys, this is why you get shot peened surfaces on some bicycle parts
for a yoyo i think extra hardness is unlikely to be a desirable unless you plan on walking the dog on concrete a bunch, in which case soemthing like the hardcoat onedrop used to offer would be better, or just using a harder metal on the rims, (like, steel or, titanium or tungsten)
cool idea though, it would be fun experiment to try if you happen to have a cnc lathe, a kiln and a lot of time
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looking at my oasis, I would think you would have to make sure it’s a more hefty yoyo with some thick walls. I don’t see it coming out without a lot of vibe though, my only fear would be it fully cracking on any type of impact
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I was wondering if the type of steel typically used in full-stainless yoyos would technically work for hardening via high-temperature and oil quenching?
I understand the question. Most steels used in yoyos are in the 303/304 alloy family if I’m not misstaken. They are steels that already barely respond to heat treatment in general.
The critical factor here would be the Carbon content.
Please note that this is at only 0.1%
there is an almost direct connection between carbon content and hardenability (at least in 95+% of cases).
Knife steel with a content below 0.6% is seen as virtually useless for it’s application. 0.1% really makes me suspect it won’t get very much harder than it is in annealed state.
And then there’s the other factor. Warp during quench.
The Quench is possibly the second most violent treatment you can give the steel (the first being forging) and steel objects can literally rip themselves apart during it if proportions/temperature etc are in any way off.
This would pose an extra fairly high risk for something that in an object like this using this alloy would yield very few benefits.
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If you are successful at heat treating and hardening of the steel you now have to address the scale that is formed in the process that would have to be machined off.
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Yeah I also looked up what austenitic means and due to the high nickel content and cubic structure too there isn’t that much room to harden anything due to the crystal structure either lol. That being said you’re right there’s like, next to no carbon in there. Also thank you for the very detailed answer as this fired the neurons in my brain 
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Very true. Hence the whole “I could try it, but probably shouldn’t” thing. Especially if it warps 
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There are Argon or otherwise oxygen low ovens. But yeah. Steel at high temperatur in contact with oxygen is also a factor for problems.
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Another option I’ve heard knife makers using is sacrificial material in the foil wrap that will burn and suck up the oxygen around the steel.
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Yeah that works. Still leaves some scale just not much. Also doesn’t negate the other issues. Just the oxygen one.
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I’ve been doing some research on this myself recently! Most yo-yos are indeed machined from 303 or 304 which don’t heat treat well. I have in my head an idea for a steel fixie with changeable scales, like a knife so I’ve been doing a bit of steel research to see how I could make the absolute toughest yoyo possible.
I believe the most appropriate steel my machine shop has on hand is S7, followed by A2. Both are considered tool steels often used for things like hammers and chisels. They are air quenched instead of oil quenched steels so the heat treatment process is a little simpler. After heat treatment they would need to be tempered to reintroduce a little flex into them. The benefit of them being air quenched is that there is less chance of warping during the process.
The downside to having a yoyo as tough as a hammer is it isn’t a stainless steel and would need to be protected from moisture to avoid rust forming.
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this discussion makes me curious about doing some kind of gun bluing on a steel throw.
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Both these steels WILL corrode in time on a yoyo.
And yes, they are air quenched. But they also need more precise temps than most oil quenched steels do.
S7 really isn’t very corrosion resistant. It IS the stronger of the two and would be fun to have something like it for 5a or such. But will not hold up to moisture very well.
A2 would do better in that regard. Less shock proof but I doubt that would be an issue.
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Powdercoat? My dad has a powder coating operation at the one machine shop he worked at and that stuff is tough as nails.
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