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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 02-11-2010, 04:34 PM
mrgantz mrgantz is offline
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Re-Heat Treat?

Ok, working on my first knife made from a Nicholson (fine) file. Originally Rockwell 60, annealed at the shop in the plant at 1500 degrees to a Rockwell hardness of about 30. Finished out the knife with grinder and sandpaper. Took it back to the plant where the shop guy heat treated it at 1500 degrees, quenched and then "drew it back" in the kiln at 700 degrees. Final product was a whopping Rockwell hardness of about 45.

Question: should I re-heat treat at 1500 and quench in hopes of bringing the hardness back up or just finish it out at 45. I am not trying to go for a fancy polished knife, just a workable tool that I can cut with. Thoughts?
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Old 02-11-2010, 05:30 PM
Ed Tipton Ed Tipton is offline
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I would re-HT that puppy. RC 45 just isn't hard enough for a knife that you intend to work with. In my experience in forging files, I think your 1500 degrees is probably OK, but try tempering between 450 and 500 degrees for about two hours. Multiple cycles will not hurt and could improve the final results. That should give you a finished blade somewhere in the rc 58-60 range which is much better suited for a utility knife.
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Old 02-11-2010, 08:54 PM
mrgantz mrgantz is offline
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Thanks. I dont have access to the plant kiln for a couple of weeks, so I may try to build a simple forge. Propane + coffee can or brake drum + coal?
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Old 02-12-2010, 02:08 AM
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sdcb27 sdcb27 is offline
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First, are you sure its hardenable steel? Like did you test the tang by quenching it and seeing it it snapped off? Second, what did you quench in and how long did you leave it in?


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Old 02-12-2010, 03:42 AM
Ed Tipton Ed Tipton is offline
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I assumed that since you were working with a Nicholson file, that the file was initially through-hardened to RC-60. That is what I would expect to find, however, checking the hardness after quenching just to verify the hardness and the technique you used were effective is easily done...and worth the effort. Assuming you have succeeded in re-hardening the file by quenching, it should then be "tempered". In my shop, I do this with a simple toaster oven...and it works quite well. Setting the oven to it's max temperature and leaving the knife in for about two hours should produce a good utility knife. If possible, try to guard against the knife being exposed to the direct radiant heat of the element by sitting it on a sheet and covering with acover to shield from the direct heat of the element. If you don't have a toaster oven, the standard kitchen oven can be used. Monitor it during the process, and stop the process when it turns the color of beer and before the knife turns blue. Understand, this is a technique for creating a good usable work knife, and is not offered as the ultimate in heat treating. This is something that anyone can do in the comfort of their own home, using equipment they already have on hand.
When hardening, heat the knife as uniformly as possible until it is no longer magnetic, and then very quickly quench it in water....cross your fingers...and hope it does not crack. Be certain to remove all of the grind marks and "teeth" from the file prior to quenching as these will become stress risers and could induce cracking. A failed first attempt is not uncommon. Also, check to make sure that the knife is straight since you will likely encounter some warping. Exercise patience and lots of attention to detail. You will learn a lot.
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