differential hardening vs differential temper

G

GABaus

Joined
May 7, 2017
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This is not a pro con question. I am making a bowie out of 1095 which would preferably in addition to being a decent knife would have a hamon (for aesthetic reasons) and at least an 1/8 inch thick strip along the spine that is relatively hard(think spring temper)
more specifically the question is if I can use clay to produce a hamon while leaving the spine exposed to harden, or will it probably just fall off (in which case I should just differentially temper the blade)
 
The clay shouldn't fall off. Many makers make cool hamons where the spin is uncovered. What would you be using for clay?
Just make sure it is dried properly. If it is not dried it will want to pop off.
 
Thanks for the replies/answers.
I am unsure on type of clay, perhaps some I refine from the soil mixed with wood ashes (or a pre made refractory material like Satenite if I am not feeling adventurous)
 
what does it mean to differentially temper? seriously :-)
how is this possible? and what is the value of it?

regards
 
Spring temper is 2 hrs. @ 950°F, and regular temper is 450°? Clay would work for a few seconds, not several hours. How would you plan to keep the 500°F difference for 2 hours?
 
HSC /// said:
what does it mean to differentially temper? seriously :)
how is this possible? and what is the value of it?

regards
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Differential tempering consists of heating the spine of the knife with a torch or other heat source to partially soften it improving toughness.
 
Atlas Knife Company said:
Spring temper is 2 hrs. @ 950°F, and regular temper is 450°? Clay would work for a few seconds, not several hours. How would you plan to keep the 500°F difference for 2 hours?
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The clay prevents hardening in the first place. Spring temper is simply an approximation of the softest I would want the spine but in reality with a differential temper it would probably end up harder. To maintain a temperature difference takes a combination of controlled application of heat(usually with a torch or hot bar of steel) and keeping the edge cool by submerging it in water.
 
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You are wanting a hamon, so differential heat treatment is the only way. If it was the performance characteristics of a softer spine you were after, I would go with selective tempering. IMO, tempered martensite is better than a mixed structure. If you are looking for a knife to bend in a vice, do both.
 
Rick Marchand said:
You are wanting a hamon, so differential heat treatmeTnt is the only way. If it was the performance characteristics of a softer spine you were after, I would go with selective tempering. IMO, tempered martensite is better than a mixed structure. If you are looking for a knife to bend in a vice, do both.
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If at all possible, hardening the entire blade is preferable as stated above by Rick. The structure of the steel is much more sound when the entire blade is quenched. Going for a hamon requires the use of clay and there for ending up with a blade with 100 % martensite is not possible. The structure under the clay is different than the uncovered steel. Selective hardening of the blade will result in a hamon but will not give you the complex hamon that clay does.
What ever the process, stress relief along the spine, at the ricasso and through the tang is a must. There is nothing more embarrassing than having a knife returned to you with a blade that broke right at the guard (where the steel should have been at spring temper).
 
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