Repeated heat treat question...carbon loss?

[C_Claycomb]

Can anyone give me an idea of how many times one can (try to) heat treat a blade of O-1 before wrecking it? I have been attempting to heat treat a small blade ( 2” x 0.5” x 1/8”) using a propane torch. This is my test/practice blade. At present it is mostly hardened, all but the rear-most 1/8 of edge, the hardened area runs from the tip to a line starting halfway down the spine and going diagonally to just in front of the riccaso. I am not real pleased, but it took 4 tries to get it to this point and I am worried that to carry on will have some sort of adverse affect on the steel. As it is now its edge is hard, if I try to harden it again (having sharpened it once) will I ruin it. I have heard that carbon leaves the steel during heating, but am unclear about the temperature and effect.

Also, should a blade fail to get fully hardened, what is the correct procedure? Does it need to be annealed again before another hardening cycle is attempted? My problem with hardening seems to be getting the entire blade all the way to non-magnetic, I have read that this is also what is needed to anneal it.

Thanks

Chris

 

[blackboogers]

Dont sweat it you can retry pretty much as you want. You will only burn out the carbon if you take too far over critical heat. Obviously you dont want too retry 4 or 6 times. But if you really want to play it safe you can anneal by taking it to critical heat and letting it cool in some vermiculite (get it ay any garden store its used to condition soil) The cooling takes hours so heat it and let it sit over night.

 

[Ed Fowler]

Rex once shot some chemistries on a blade that had been subjected to the triple quench. The first chemistry was on the scale of the blade, showed a loss of one point carbon. He polished off a few thousands and was right back to the origonal chemistry of the parent stock that was a 5 1/2 inch round bar. I have never seen multiple quench hurt the cutting performance of the steel. I have the most experience with 5160 and 52100. Other steels may vary, but some simple performance teats in your shop will reveal the nature of the blade. ie. edge flex, rope cut, and 90 degreee flex.

 

[C_Claycomb]

Thanks for the replies. After posting I started doing a little more research and discovered that I had the answer to my question all along, it was right there in Ed Fowler’s book…Doh! Thanks for the confirmation though. I am still new enough at this game that I like seeing everything in triplicate!

After reading that I would not, in fact, end up with scrap if I tried repeated quench cycles I went back and tried again, this time I succeeded in hardening the entire blade, as I wanted. It takes a great edge and time will tell how it holds up. It cuts rope pretty well now, I think though that I will forgo that 90degree flex! Just seeing photos of those test scares me!!

Thanks again. Really looking forward to finishing my first all-home-made knife. This heat treating thing is fun!

 

[richard rosvall]

Congratulations, Chris. Just a thought, you might want to try a MAPP gas cylinder if you are using a small propane torch. It burns a lot hotter than propane.