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Differential hardening with clay question

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Good afternoon friends. 

I just recently started using clay and trying to do differential hardening instead of a full quench. I'm working with some thin blades and thought it would be  good to have the flexibility being of a softer back. Also like the hamon line on these longer blades. I'm working with o1 steel 1/8 " thick . 

My question is after I have heated and soaked the blade in the forge. I only do an edge quench, I don't submerge the whole blade. That leaves the clayed part of the blade still very hot. Do I need to remove the clay as soon as possible after the quenching process to keep the residual heat from migrating back into the quenched area of the blade. Or does it matter. I've noticed sometimes it flakes off on its own and it's still glowing red inside and just has me concerned.   


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Thanks  Steve 

 My main question  was will the heat still trapped in the clay affect the hardness of the edge that was quenched. Or do I need to get the clay off as soon after the quenching as possible. 

My question was directed more towards the hardness of the blade rather than the hamon as a byproduct. 

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  • 3 weeks later...

If you allow the heat to migrate back into the hardened edge it will start to temper the edge. If allowed to continue it will continue to temper the edge back to it's original soft state. If you want the edge to remain as hardened, as quenched, continue to keep the edge cooled until the heat drops in the remainder of the blade to under 400 deg. The slower cooling of the spine will keep it in the tougher/softer state you desire. You can also quickly abrade the edge to reveal clean shiny steel and allow the heat to temper the edge, observing the color changes and re-quenching when the edge tempers to the desired light to straw color that yields a hard yet tough edge on the blade. Treating in an acid etch after cleaning may etch the different temper zones differentially and give you a visual indication of a hamon. Just my two cents.



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On 11/9/2017 at 2:00 AM, Johnnyreb338 said:

I only do an edge quench, I don't submerge the whole blade.

If you are only doing an edge quench, claying the blade is probably superfluous. The auto-tempering process described by Angelfire has worked for me before, but I've only used it on struck tools (chisels and the like), and projects with a lot more mass than thin kitchen knives (hammer heads and axes).  I'm not sure how well it would work on 1/8" O1.

Note: to get maximum performance from O1 you should be heat treating with an oven or salt bath that can soak the steel at austenitizing temperatures for at least 10 minutes before quenching, otherwise you might as well use 1084.  Looking at the TTT diagram for O1 is also instructive.  It indicates that the required quench speed is appreciably slower than 1084, but I"m not completely sure how that effects the desired differential hardening you are looking for.

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