Advice on plate quenching stainless

S

StuNY

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Feb 16, 2014
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152
I have my DIY heat treat oven working at last so ready to start heat treating my stainless CPM 154 blades. I have everything to do plate quenching but before I dive in thought I should ask for some advice. Everything I have read here indicates that this is the preferred method but I have two concerns:

It seems that if I pre-grind my bevels before heat treat (like I did before sending to Peter's for last few) I will be quenching the spine and flats but not as effectively cooling the ground edge? Will this affect the hardness of the cutting edge? I know the hardness tester works on the flat surfaces so may not measure this?

On my last O1 blade (oil quench), I did a tapered tang and really like the balance I got, but won't this make it even less effective for plate quenching? It seems that I will only have contact with a small part of the blade- ricasso- but the rest will cool more slowly? I am planning to use the stainless foil wrap of course.

I am sure everyone has resolved this to work well based on the popularity of plate quenching but would appreciate any guidance.

Thanks,
Stuart
 
Stuart,
Stainless steels are air quenching steels, meaning they will harden by themselves as they cool. They don't really need the super fast cooling speeds like oil quenching steels.
Plate quenching is the standard method for air hardening steels because it works better than just laying the blade on the table and coming back to find it bowed while cooling. One way you can help to cool the edge if you are really concerned about it is to blast the edge with cool air from a compressor as you push the plates down, although this isn't really all that necessary.
 
Plate quenching can be great, it just depends on the steel.

For high alloy steels that are supposed to be quenched fast (like CPM154, CPM3V, etc) plate quenching is a good clean alternative to oil. Yes, the edge isn't in contact with the plate, but the edge has very little thermal mass compared to the spine/tang of the blade where there's more material. Removing all that heat from the spine/tang allows the edge to cool quickly still as it's not being 're-heated' by the heat from the tang and such. You'll be making physical contact with a large part of the spine of the knife, and that will help keep everything straight as well.

Tapered tangs definitely make life harder for plate quenching, perhaps taper your tang on the grinder after HT?

Cryo or sub-zero would generally be recommended right after the plate quench especially for high alloy steels like CPM154/CPM3V.

For my A2 blades I prefer to air cool them in still air as I've found that plate quenching seems to be a little fast for A2. When plate quenched it loses some toughness and edge retention even though the hardness is about the same. To achieve this without warping I open the kiln, then attach a spring clamp to each foil envelope, pull it out and hang the whole thing on a hook using a hole drilled in the spring clamp. That way there's still air all around the blade and this pretty much staves off warping. If one side of your blade is too close to a surface that side will cool more slowly and the blade will warp. I arrange my blades in the kiln so when I pull them out they're hanging vertically with their tips up to avoid putting weight on that thin part of the blade.

Also: when I'm heat-treating these days I like to coat my blades in a light coat of anti-scale (ATP-641) and then put them in stainless foil envelopes. I find either foil or anti-scale by themselves often leave me with issues, but together the blades come out very clean. Just a few minutes sanding by hand or on the grinder gets them back to exactly how they were before they went in the kiln. I'm perfectly comfortable hand-finishing blades to 600 grit before heat-treat using this method and have had zero problems so far.
 
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