preparing to heat treat

P

pso

Joined
Oct 29, 1998
Messages
494
Hello

I have a kitchen knife that I have filed out of a piece of 1/16" thick, anealed 1074 (15LM) from a sawmill bandsaw blade by Sandvik. Blade length is 6". Overall length is 10". It is flat ground. I have sanded the blade to a 400 grit finish by hand.

I have two questions.

The first is, should I trim away some of the material at the thin cutting edge to prevent cracking? I originally filed it down to between 1/32" and 1/64". The sanding has brought it down to esentially zero. From what I have read here, I am concerned that the thin edge will crack when I quench the blade. If it will not crack, I would have a really thin flat grind and would only have to do the final cosmetic finish sanding and sharpen on my Sharpmaker.

The second is regarding the choice of heat treating procedures. The blade is extremely soft now with no springiness at all. I would most likely heat the blade up with a torch before the quench. Should I
a) Quench the whole blade, then temper the whole blade in a toaster oven twice at 400F for an hour each time.
b) Quench the whole blade, then temper the back with a torch to spring temper, then temper the rest of the blade (the edge) in a toaster oven.
c) Quench only the edge, then temper in a toaster oven. If I do this, would the edge still be really soft?
d) Some other heat treat procedure.

Thanks in advance for your help. I wouldn't have gotten as far as I have on my own.

Phil
 
Phil, I used to grind close to finish. I have changed my knifemaking a lot due comments from many very talented knifemakers here. I now leave a lot to be finished after the heat treat. I think Mr Fowler said he leaves as much as 1/8. It would be foolish to ignore the years of experimentation he has done. It is however, a little difficult to leave 1/8 on 1/16 stock. The thin stock you are working with is a nightmare for me because it's difficult for me to grind the whippy stuff and it needs to be heat treated carefully. I would not have gone to 400 grit. I like to stop at 220 max before I heat it.

Anyway, with yours I would bring it up slowly and quench in a warm quench. I doubt it will crack but sometimes they do no matter what. Don't forget to normalize. That's very important both for edge holding qualities and to remove stress within the steel. Any of the tempering methods work but I confess I edge quench and use the old toaster oven a lot.
 
I second what Peter said. If you don't have a grinder (since you mentioned that you used files I'll assume you don't) you almost have to finish the blade as close as you can before heat treat. I regularly go to 320 grit finish and anywhere from 1/64" to 1/32" on the edge when I am using hand tools only. Since I have my grinder set up now I'll probably modify my methods somewhat to include more grinding and finishing after heat treat. Be extra careful when heating that thin blade up. It will get to critical before you know it (especially watch the tip!) and quench in warm (120-130 degrees)oil. I would try an edge quench. Just normalize (heat to just critical and then let the red fade out of the blade in still air until it's black) heat back up to critical and quench, test with a dull file to see that it hardened, then temper for an hour, 400 degrees F should be about right, let the blade cool to room temp and temper again for another hour.
 
I got carried away flat grinding some 1/8" O1 'till the edge was really thin. When i quenched it I got the most interesting wavy warpage. No cracks and the waves ground out.
 
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