Subject: Differential Heat-Treatment

From: [email-masked]
Date: Thu, 14 Jan 1993 12:26:50 GMT

Hello again,
One of the best features of a bladesmith forged and heat-treated knife is
it's differential heat-treat. This can be done two different ways:
(1) Assuming you have normalized the blade after forging it to shape and
ground it to 90% completion. You slowly heat the blade with edge up in the 
fire. When the entire blade gets to critical, quench in whatever medium you
have chosen(I prefer pre-heated oil). Be very careful at this point because
the blade is very brittle at this point. Holding the blade with 1/2 inch of
the edge submerged in water,use a propane torch to heat the back of the blade
to a dark blue,then quench the entire blade to stop the color run. Now bake
the blade in the kitchen oven at 400 degrees for one hour. Now you have a 
blade with a hard edge but a soft back making it less likely to break under
stress.
(2) Again assuming that you have normalized after forging. Heat only the 
edge to critical leaving the back still black then quench. By hardening 
only the edge you have eliminated the propane torch step mentioned above.
Now bake blade in the oven at 400 degrees for one hour and presto-changeo
you have a differential heat-treated blade.

Good luck
John Sugg
Yellow Hammer Forge 
Waverly,Alabama USA