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Originally Posted by mirwa
Mmm, cryo treatment of nickle silver defies all logic to me, not saying it does not work as I really not up to date on cryo treating, but nothing in the mix can harden vee temperature variations.
I was taught mettalurgy as part of an apprenticeship i did in my younger years, nickle silve is typically copper, zinc and nickle, this composition only gets harder through cold working, we use heat to soften it again.
If a customer wants hard nickle silver you can roll it and then unroll it and roll it again a few times, this will dramatically increase the hardness
Steve
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I hadn't given it much thought but it appears that is what the science states.
One discussion of it is as follows:
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Understanding why sub cooling is effective on some materials and not on others is actually a pretty deep dive into metallurgy. It required understanding of metal phases and phase transformations, heat treatment, development of rapid cooling non-equilibrium constituents, crystal structure, TTT and CCT curves and material density. Probably the best thing to do is read up on heat treatment of tool steels for dimensional stability. Steels are hardenable by heat treatment. At high temps the structure is FCC austenite. Cooled slowly enough and with low enough alloying, the austenite transforms to the equilibrium phase BCC ferrite. Cool fast enough and you get a very hard strong (but sometimes brittle) non-equilibrium BCT phase called martensite. This phase has a different density than the room temp equilibrium phase ferrite or the high temp equilibrium phase austenite. Depending on the amount and type of alloying elements, not all of the austenite may transform to martensite since alloying can impede the movement of atoms. The inability of the atoms to move around is how we get martensite anyway. If the movement is slowed down enough we get what is called retained austenite. This retained austenite is not as hard as martensite and has a different density. Bad because it gives non-uniform properties and can lead to dimensional instability. A couple of things can get rid of retained austenite. Applied loads (like tool steels often get in service) can cause the retained austenite to transform to martensite. This results in shape changes which is a bad outcome for many tool steel applications. Subcooling also causes the austenite to transform to martensite. This gives a uniform structure with dimensional stability and consistent properties.
Thusly cryo treatment of tool steels. It is real, it works and it is done.
Nickel silver (copper, nickel and zinc) is basically a single phase austenitic structure that undergoes no phase change from solidification to room temperature. It is considered a non-hardenable by heat treatment alloy. So it will stay austenite even if subcooled. No non equilibrium phase so no hardening. Same for 300 series stainless steel, non-alloyed copper, all do not undergo phase transformations and are non-hardenable by heat treatment.
There is such a thing as strain hardening which is why it gets more difficult bend a wire each time it is bent. Cool rapid enough and deep enough and a certain amount of strain hardening is possible for non-heat treatable alloys since rapid enough cooling can induce strains in the material. However the simple act of bending fret wire to the shape of the fret board will induce much more strain hardening than would be achieved by subcooling. Erlewine even recognized the potential benefit in increased hardness that can come from overbending and unbending fret wire prior to installation.
Key take away is just because it works one place it may not really work much in another place however logical it may seem on the surface. There is more than I was willing to type here and this may confuse more than it helps but it is a view into what is going on.
hunter
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From:
https://www.thegearpage.net/board/in...frets.1918375/
A scientific study on Nickel-titanium concluded the following:
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Cryogenic treatment resulted in increased microhardness, but this increase was not detected clinically. There was no measurable change in elemental or crystalline phase composition.
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From:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1266290/
It appears that Gibson started the cryo fret thing:
https://www.youtube.com/watch?v=PmkVxzeKttM
The description of it in the video isn't very scientific: it suggests marketing with little substantiating evidence.
Stewmac's description of it is subjective:
https://www.stewmac.com/luthier-tool...-fretwire.html
It seems unlikely to be an improvement, but, it isn't more expensive than regular fret wire. If one believes in the marketing, no reason not to try it, despite there not being substantiating science behind the claims.