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Hardening issue: Farrier's rasp


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I forged out a rough kukri-esque shape from some farrier's rasp, full tang, ground to about the thickness of a dime, maybe a little thicker, and quenched in canola-water at critical. Didn't harden up, seemed to be a little tough to get through but the file did bite in quite a bit. Ideas on the why's and how to avoid it in the future?

My first thought was maybe the rasp was case hardened, but the brand, "Save Edge", is a carbon steel and not case hardened.

My next guess was maybe I decarburized it during forging or something, this is my most likely guess, as with my recently completing a venturi torch the heat is quite much for the paint can forge I have. But, another smith said it looked to clean and not crispy enough for that. Any thoughts? I tried normalizing again, ground a little off the edge to make it thicker, did an interrupted quench, then eventually a plain water quench. Not so much as a crack.

 

Here are some images just after forging: https://www.instagram.com/p/97SLrskPZ4/?taken-by=bladesofbelaq

https://www.instagram.com/p/964t4DEPQg/?taken-by=bladesofbelaq

Think decarb is the explanation? I forged another blade from the same rasp and it seemed to harden up fine.

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Interesting issue. Could be a number of things ... what exactly is your quenching medium? 'Canola- water' ... ? As you mentioned, I don't think the blade decarburized enough in your gas forge to not be hardening at all. The brand " Save Edge" sounds like a newer ,cheap import tool... I would suggest that there is the possibility of some inconsistency in the steel itself. That would explain why the other blade hardened.

 

There is also the consideration that you are working with an unknown alloy. It is very possible that your quench process is not ideal or even close to what is needed to correctly and fully harden the blade.

 

Did you only file test the edge, or did you also try along the spine to see if the thicker section hardened ? Have you tried breaking a section to to see what kind of grain structure you are getting?

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I'll also throw out that I have tested a rasp on the spectrometer and found it to have about 0.20% carbon, and have seen others that have successfully made knives from the same brand. I can't remember for sure what brand it was, this was a couple years ago, but I'm think it was Heller. As Isaac says, could just be a quality control issue on on the rasp manufacturer side.

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No, probably case hardened. That goes away if ground or forged, it's only a thin skin. I thought Save-Edge was a decent brand. Maybe they're all cutting corners now.

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To save yourself grief in the future, if you decide to make a knife from a file or rasp.... heat the tang to just past critical and quickly quench it in water. Clamp it in a vise, and whack the tang with a hammer (wear eye protection, and don't use your favorite hammer). If it breaks, it is good carbon steel... if it bends, it is probably case-hardened.

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  • 2 weeks later...

Throwing in a Farriers perspective, those are some of the lowest quality and cheapest rasp on the market. They will literally only work on your first three horses and then aren't sharp enough to even produce filings. I'm newer to hardening and qeunching for blades, but my view is that they are so cheaply made it's hard to say whether or not it's even close to the same material rasp to rasp.

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