Salt bath heat treater

Larrin

Knifemaker / Craftsman / Service Provider
Joined
Jan 17, 2004
Messages
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Is there anyone that offers salt bath heat treatment? I'm looking for someone that would be able to do two quenches at two different temperatures, followed by cryo, and then tempering of course. It's stainless so the austenitizing temperature is fairly high, 1925-1975F.
 
Well this thread has made it down to the second page with hardly a second glance, though I didn't think there was anybody out there anyway.
 
Larrin,
Weve all looked it over. You are no stranger to this process so Im wondering why you dont do it yourself except maybe you dont have the salt pots but we know you can do the same thing easier in the electric oven.

So tell us about your experiment and maybe you will get a bite.

Ive never done stainless in my salt pot. Its un-nerving enough at 1500f let alone 1950f so call me a wuss. :)
 
Hey Larrin-


I would have thought your dad had a salt bath.

My set-up is digitally controlled and works very well, but my salt isn't stable at that high of a temp. That's probably going to be your hang-up on this one... most of the salts that guys are using in bladesmith shops peter-out around 1800F.

Sorry, I would have loved to help! :(
 
I'm moving away from home (again), and I won't have access to 220/240V power. I've found a heat treater that will use the traditional kiln for my heat treatment that I've already been performing, but salt pots are intriguing to me. The much faster and more uniform heating of the salt pots can mean a much finer grain size, at least according to some sources. The two quenches at two different temperatures is something I've been experimenting with over the past month or so. A multiple quench as we typically know it is actually counter-productive with air hardening and stainless steels, where with simple carbon steels and forging alloys can be multiple quenched at the same temperature for grain refinement. Using a lower temperature for the first quench can give the same effect with air hardening and stainless steels.

Salt pots also scare me, even if I could purchase them myself and use them, which is another reason to find somebody else who would offer salt bath heat treatment to others, but I've never known of anybody to do it, and knifemakers that have their own salt pots that might be willing to heat treat for others generally heat treat carbon steels with much lower austenitizing temepratures.

Edit: Thanks Nick, it was also apparent to me that the high temperature would probably be the hang up here, but I figured it was worth a try. Oh, and my dad doesn't have salt baths.
 
hmm, I have a 50/50 mix of sodium & calcium chloride, I saw it mentioned here as a usable mixture. boiling point for the NaCl is above 2600F. What other salts are used, I would figure my mix would be okay at a temp 700 degrees below boiling.

I'm still sorting everything out with the controller and gas valve, also looking for another way to deliver air. Only got it to 1830 in a test run. I'd give it a shot if I can get up to temp and hold comfortably.
 
Thanks hardheart, keep me updated. I am looking for someone who can do heat treating fairly regularly if that wouldn't be a problem for you. I won't be making a lot of knives, but one or occasionally two a week wouldn't surprise me in the future.

Oh, and I forgot to mention that greater hardness is a possibility with the salt pots.
 
Larrin,

I've been mulling around the idea of starting up a heat treat shop here in Knoxville for a few months. At the moment, the nearest ones I know of are 60 miles away. After I get through the Blade Show rush, I plan to spend some time researching this business idea. If I do it, I plan to do industrial heat treating as well as offer services to knifemakers as well. The whole thing is a ways off in the future, but I just thought I'd throw that info your way for future reference. I've got several furnaces and salt pots, and hadn't considered salt bath heat treating of stainless, but you've planted that idea in my head now...

:)

-Darren

p.s. what is the temp for the secondary quench?
 
According to "Tool Steels" the prequench has a fairly large range, it's 1600-1800F with D2 and 1600-1900F with M2. I think the range is large because all you have to do is form austenite, which occurs at a fairly low temperature, it varies by steel but it's usually somewhere between 1550 and 1650F (can't remember exactly). Anyway, with AEB-L I've been using 1750F and 1975F, though with salt baths I might drop that 1975F down to 1925F, it depends on what kind of hardness I get.

Darren, once you get up and running make sure to contact me, I would definitely be interested. By the way, if my sources are correct and you could get a finer grain size using the shorter soak times provided by a salt bath, then micrographs showing so would be very intriguing to makers looking for the highest performance possible.
 
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