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Old 05-24-2017, 07:50 AM
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Originally Posted by Drm50 View Post
The making of a correctly tempered blade is the key to knife
making. Guys that know how to do this are artist in their own
right. I have made a lot of knives but have mostly failed in
tempering process. Which I attempted while making knives out
of files. I take the easy way out and look for items of carbon
steel that are already tempered. Actually this is about the same
as making a "kit" knife. Believe me there are a lot more Handle
artists than blade smiths.
Take that file and put it in your oven at 425f for 2 hours, then cool it off, then do 2 more hours at 425f. If the steel is still to hard and has edge chipping take it to 450f. Some guys lay the side of a thin edge on a piece of brass round stock and pull it across with a bit of pressure. Should deflect slightly, but go back to straight. If it gets little chips in the edge up temper temperature. If it stays deformed your temper was to hot. I have a hardness tester and use that to tell me whats happening when I temper. I also use a digitally controlled oven for both hardening and tempering.

Reason for second temper is that a certain percentage of the steel gets stuck as Austensite when quenching. This converts to hard Martensite on the first temper. That percentage of steel needs 2nd temper to become tempered. Very little of the matrix will be left a austensite doing a double temper on simple high carbon steels. On complex alloy steels like 440C and D2 it helpd the steel all complete the transformation from austensite to martensite to super cool the steel before tempering. I use a bath of acetone and dry ice to do this, some guys use liquid nitrogen. Which is hard to get when you live over 100 miles from anywhere.

Hardening happens really fast. With straight high carbon steels like 1095 you have .8 of a second to quench from 1350 to 750 (you have seconds between 1500 and 1350) Air harden steels like D2 you have about 8-10 seconds to cool it. That is to harden it.


Tempering is different. It takes time for the Martensite formed by hardening it to get reformed. Some people simply heat the blade up to say 425, this will cause some tempering, BUT, it will not allow complete transformation. Temper-time temper time.

Last edited by steelslaver; 05-24-2017 at 08:01 AM.
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