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Tim Crocker

Vertical Quench Question

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For quenching, there is the Leidenfrost effect where a vapor  gap occurs and the cooling rate is relatively low until the temperature drops enough for wetting. Upon wetting the cooling rate increases significantly. With metal thickness on a bevel, and this effect, I have seen natural hamon occur in a horizontal quench. In a vertical quench the Leidenfrost effect causes the wetting transition to progress up the knife or sword, so in my mind this means the higher up the piece the slower the overall quench rate and therefore an influence on the hardness from tip to end. Convection in the quenchant also takes place, which could affect cooling rate. Is this effect significant enough to cause a concerning difference in hardness along a piece quenched in a vertical tank? If so, is there a recommended limitation on blade length for vertical quench (understanding different cooling rates for different alloys)?

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All of the following assumes modern steels:

Short answer: I would say no.  

Longer answer:  The upper limit on length would be a practical limit on a size that a person could wield (e.g. a ridiculously large Montante) before it would be a quenching concern.  Unless your quench was pretty borderline to begin with (like if you were trying to quench a barely hardenable material in oil that was nearing its flash-point).  If you are dealing with hamon forming materials, then this means you are near the limit of the quench, but if you choose the proper quench medium (one designed to not form a vapor gap), the Leidenfrost effect is pretty much non-existent, and you really have to just worry about convection (besides alloy and geometry, of course).  Having a large volume of quenchant does the trick there.  

Remember, the goal for through hardening is always to quench as slowing as possible while still achieving 100% martensitic conversion.  Throwing in a hamon makes this more difficult because you are trying to achieve 2 things now (fast enough here, but also slow enough there).  This is very difficult when going for an auto-hamon.  

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Thank you. I made a vertical tank but have been hesitant to use it until I had better understanding of this. I knocked over my horizontal quench tank. It took four hours to properly clean up. It gave me new motivation to do the further research for the vertical tank.

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The appearance of a hamon will depend, at least in part, on the alloy that you choose and the grain in your steel.  Depth of hardening increases with grain size.  If you choose something like 1075 with fine grain structure it will automatically form a hamon, at least if you polish it out or etch it.  That's the auto-hamon that Jerrod referred to.

As far as the tank goes secure it to something so that it doesn't fall over or use something that is by nature stable, like a turkey fryer.  Even then it wouldn't hurt to secure it to something.

Doug

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