High Temp Salt Bath

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Mobius1

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Feb 15, 2016
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I have been wanting to get into using salt baths for some time now, and thanks to Evenheat's new line of them (https://usaknifemaker.com/evenheat-sb-718.html), I'm even more interested. My current heat treating ovens are also a large compromise for me (110v :(), so I have been wanting to upgrade to a new 220v kiln anyways.

But it seems like most people aren't going over 1600 degrees with their salt baths, but I would want it specifically for air hardening and stainless steels, which I typically heat to 1950.

I don't use aluminum plates or air to quench, but oil. This is yet another reason why a salt bath seems so appealing, since decarb would no longer be an issue (No more SS foil!).

If I were to go this route, are the salts non-toxic? I found a website, Heatbath.com, which advertises salts of the correct temperature range, but I haven't been able to find any anywhere else.

Does anyone here use salt baths at 1900+ degree temps? If so, where do you get your salts, and what is the cost? Also, I'm open to any encouragement or discouragement from going this route! :D
 
Salt bath heat treating is pretty common for high speed steels. So the technical feasibility is good.
 
I just had two salt pots delivered yesterday.

I won't be using them for high temp stainless HT. I will use the HT oven for that.

My take on why there isn't much small shop interest in stainless salt pot HT is:
Safety concerns - Besides the fact that you have a captive tank of lava, the thought of a pot failure at 2000F is beyond scary. Shop practices around the pots will require some adjustments. You will need a safe place with plenty of room where the pots can sit for hours at temperature with no activities going on around them. ONE drop of water can cause a volcanic eruption.
Costs - They are expensive - Around $2200-2500 plus the pot. The pots won't last as long for high temp HT and a schedule 80 pot is around $800. I don't think a schedule 40n pot would be wise for 2000F HT. The high temp austinitization salts aren't too much trouble to get, but the low temp tempering salts can't be purchased just anyplace, and since 911 you have to get checked out before the places that carry the salts will ship to you. The Feds are notified about the purchase, too (not a concern for me, but there are some folks who won't like this).
Quality - Not much to gain in HT quality over foil packets in a good oven.
Unfamiliarity - Most makers with a few years experience have oven HT down pretty tight. The pots will be a whole new learning curve, perhaps with different parameters.
Compatibility - The socket your HT oven plugs into may not be suitable. These pots draw a LOT of current. EACH pot needs at least a 30 amp 220V dedicated circuit (only that one socket), with 40 amps being a better idea.The high temp pots may need 50 amp sockets.
Maintenance - The salts require maintaining to prevent them from eating up your blades. It isn't as easy as adjusting the ph in the swimming pool. I suspect high temp HT will increase this a lot. Most folks maintain the pot by regular addition of a certain amount of new salts. This adds to the expense.


If you really want to discuss the pros and cons, call Evenheat and ask to talk with Spencer or Mike. They are the builders/designers of Evenheat's pots.
 
Admittedly the cost is the greatest negative factor, for me. But a regular 220v oven is not exactly cheap, either. My wife is going to be about as equally angry at me either way!

As far as quality goes, my main line of thinking is that it will help to significantly increase the heat transfer when quenching in oil, because currently there is the gap of air between the foil and the blade when I quench (Of coure, I try my best to keep it at a minimum.).

Will it have a large effect on the quality? Perhaps not. Honestly, it's hard to get much information on it, since almost everyone plate quenches, and so few people use 1950 degree salt pots.

Why do I oil quench? Primarily because it seems to have a massive impact on my corrosion resistance (Primarily with 3v). Also, because I don't like making my bevels after heat treat.

To me, the ideal situation, would be austenitizing in a salt pot, and quenching in a salt pot! But for now I'm thinking of starting with the first, and sticking to the interrupted oil quench. But again, I am far from an expert, so I am very grateful for the advice.
 
If your main reason is oil quenching I don't think you need a salt bath to solve that problem. And if you think that oil quenching is giving a "massive impact on [your] corrosion resistance" we can get around that as well, since a plate quench should be more than fast enough to ensure chromium stays in solution.
 
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I have considered trying anti-scale compounds, which could help. But do they work well at 1950 degrees?

I do know there are other benefits to oil quenching, but it's been a while since I did the research on that.

But as for salt baths, I thought the main benefit to using them, was cutting down soak time, and thus giving better grain size. It wouldn't JUST be for my oil quenching reasons...
 
I'm with Larrin on this. You may be solving a problem that doesn't exist. Beyond gaining a point or so in hardness, there isn't any major metallurgical advantage to the oil quench that I know of.
 
The primary benefits of the salt bath are temperature uniformity, heating rate, and grain size control when it comes to things that aren’t primarily annoyances (using foil or grinding off decarb).
 
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