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Thursday, January 26, 2017

Cut Nail Knives

Thought I'd try using some cut nails to make knife blades from- they're a hardened, tempered steel nail used to attach things (mostly wood) to concrete.  I've never tried them, tho they are easy enough to find- the local hardware store and the nearby Homerville have them, as do other big box stores, and of course they can be had online.

I couldn't find much of any info on steel composition or working properties (annealing, hardening, tempering data); I did get a bit of info from a post to the WWI forum.

Time to experiment, and I have learned the hard way the key to successful experimenting is good note-taking.  So here they are.

First I tried annealing a nail- heat to non magnetic and left it to cool in a can of hardwood ash.  It took a long while to cool, file test showed it was soft, but not as soft as the O1 I usually use (subjective observation).

I heated non magnetic again, and quenched in brine.  Thin blades I make of O1 quench nicely with a momentary dip in brine and cool to room temp (10 min or so) in a bucket of hardwood ash.  Tried that with the annealed nail, file test said it was hard, but again (subjectively) not as hard as the O1. Either the steel composition, the quench process, or the thickness of the nail was affecting the outcome.  (Nail is approximately 1/8" thick).

So at this point I am uncertain of the annealing and the hardening process.  I needed a less subjective test for soft and hard.  I grabbed another nail and bent it till it snapped- I estimate 45 degrees.  Good start.

Annealed another nail in ashes, and one in air.  Both bent into horseshoes, but the air cooled was easier to bend.

That's progress!

On to hardening.  There are three ways to harden steel- in air, in water, and in oil.  I have been told brine and oil are essentially the same, and I believe that.  No smelly smoke or fire in the shop with brine.  Cooling the nail in air resulted in a fully annealed nail, so take air hardening off the list.  Not surprised.

Reasoning that the thickness of the nail may have affected the momentary dip in brine, I quenched the next nail in water until fully cooled.  Nail snapped at an estimated 30 degrees- harder than the original nail out of the box.  Good info, more progress.

Last test was hardening in brine until the nail was fully cool.  Nail snapped quickly, estimated at 22 degrees- sooner than the nail out of the box and sooner than the water quenched nail.

I really should test and compare quenching in oil- maybe someday.

Conclusion- Air cooling produced a superior anneal, and quenching in brine to room temp produced maximum hardness.

Tempering test is easy, but will wait until I have rough forged a few test blades.  I test temper by the size of the wire edge produced during sharpening- I'm looking for the smallest wire edge I can get.  Large edge, too soft.  Continue with additional sample and lower tempering temp until the wire edge is barely visible even under 10x magnification.  At some point the wire edge will not be continuous and Ill raise the tempering temp just a bit.  That is the combination of hardness and toughness I prefer.

Onward .

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