Heat treating with a salt pot

F

Frank Niro

Joined
Sep 10, 2000
Messages
4,786
Is the process much the same as an electric kiln in that the steel must be stressed relieved before being taken to hardening temperature and being held there for a specific length of time? Thanks. Frank
 
I just picked up some of the final parts for the salt pot I'm building, so was excited when I saw your post :). Hopefully some others with a lot more experience will add to this. For me, I think it mostly depends upon what steel you're using and the process used up to that point.

For example, I am just getting started with some stainless. Everything before this has been carbon steel and seen the inside of my forge. I did stress relieving cycles before I reached the final HT process. I believe some of the stainless steels work best with a "ramping" procedure. But I can say for some steel, get the salts to temp then just put the blade in for the prescribed time for austenization.

Not sure that actually answers your question....hopefully it helps at least a little.


Jeremy
 
Stress relieved as in normalizing should be a part of any HT process. Treat the salt pot as you would a oven. It is just a oven with molten salts that prevent scale and decarb. Please be very careful and make sure your blades and whatever you put into the pot is clean of all oil and water. Pre heat them to over 450f to ensure all moisture is driven off. A drop of water will create a volcano. Ask me how I know:confused::eek:

Most salts have about a 1550f limit. Most stainless is well over that mark. Not practical for SS ht IMHO.
 
Woops-I should've clarified in my original post... I did a fair amount of looking and researching on what "salts" I wanted to use. I landed on potash (aka, muriate of potash, potassium chloride, KCL, 0-0-62). It's the stuff that other chemicals are mixed with for fertilizers. On the data sheet, it shows as not toxic, etc (which is certainly important), melts at just a bit over 1400F and boils around 2200F. This obviously wouldn't meet the needs of many stainless steels, but for a more simple one like AEB-L, I should have no problem-1975F should keep things working nicely.

But yes-in general, an oven would be the best choice for a lot of the stainless steels. Many require specific ramp times, holding for significant time periods, etc. If nothing else, I'd figure the electricity for an oven would have to be a ways cheaper than the propane for a salt pot. And thanks for the reminder to ensure the blade is free of oils and water. I think I read or saw in one of Nick's posts that he holds the blade in front of the "vent" at the top of the pot to help dry anything out. Can't ever hear that safety stuff too much.


Jeremy
 
Just my humble opinion but I would not use the KCl salts by themselves. This is really an area you don't want to experiment with. Not only can these thing be hazardous to your health, but they can do some really nasty things to steel if not balance properly. With a little google fu you can find a document on milspec salts that gives you recipes for just about any temperature range, or the safest thing to do would be just to bite the bullet and order some salts designed for use in the range of heat you need. I use mostly carbon/tool steel so Nusal from parks metallurgical is what I went with, even though I have full access to the milspec document and all the chemicals I need to mix my own. Sometimes its just better to let those who spend millions of dollars developing things like this do the heavy lifting.
 
Matthew Lomas said:
Just my humble opinion but I would not use the KCl salts by themselves. This is really an area you don't want to experiment with. Not only can these thing be hazardous to your health, but they can do some really nasty things to steel if not balance properly. With a little google fu you can find a document on milspec salts that gives you recipes for just about any temperature range, or the safest thing to do would be just to bite the bullet and order some salts designed for use in the range of heat you need. I use mostly carbon/tool steel so Nusal from parks metallurgical is what I went with, even though I have full access to the milspec document and all the chemicals I need to mix my own. Sometimes its just better to let those who spend millions of dollars developing things like this do the heavy lifting.
Click to expand...

+++1 :thumbup: :)


Heatbath makes salts for a whole range of temperatures. Of course getting their product is a lot harder now than it used to be. I think High Temp Tools sells NuSal. That's where my last bucket came from in 2007. If you want to run various salts (with different working temp ranges) of course you'll have to have a couple/few different salt vessels, but that is certainly possible.


Frank- The steel will still need whatever thermal cycles it would need with other equipment. The only real difference is a salt pot brings steel to temp VERY fast, so the time it needs to be in the salt is typically less than a kiln (to accomplish the same thing).

Running my salt bath (basically a blown vertical forge with PID controller+ solenoid) costs pennies to run for hours at a time. :)
 
Thank you for the suggestions and advice (and sorry to the OP for any derailment here...). I looked around and found some of the different recipes to mix together, but just didn't want to go that route for some reason. It sounded as if mixing a few easily obtained chemicals worked for several different people, though. Similarly, I contacted a few different makers who've done what I would consider a significant amount of heat treating over many years and use potash in their salt pots.

I plan on taking all safety precautions as I go along-clothing/face shield/gloves/rolled outside. Thanks again, though-I always appreciate the wealth of knowledge and help on here.


Jeremy
 
Thank you all for this. I'm not going there myself, but did want the basic background information on what must be done with this method of heat treating. Frank
 
If you are interesting in mixing your own I have the pdf to MIL-S-10699B and the revision which has all the recipes. Like I said I prefer pre bought but this will keep you safer than experimenting, afterall the military mixed these for decades.
 
I use 50/50 KCl / NaCl up to 1550F with no issues. Salt pots require extreme caution to use safely; however toxicity is not an issue with KCl (Potassium Chloride). Former Chemist talking. -Doug
 
50/50 KCl/NaCl is the recipe for MIL-S-10699A # 5 with a working range of 1350-1650F. Very similar to Nusal from Parks/Heatbath. The problem with using a pure KCl is it may not be neutral for the steel. Problems with decarb, scaling, and pitting, basically negating most of the benefits of salt pots. I'm not certain that that will be the case but I know its not covered in the milspec document and I would assume they would go the easy route if it was beneficial. And it has a melting point of ~1418F which means the low end of the working range will be ~1550F, not ideal for most carbon/tool steels.
 
Thanks again! I will pass this along to my friend who is wanting this sort of information. I've been using a known name to do my heat treating and like the results he always sends back. Frank
 
Matthew-
Thanks for all the info-I'd love to get a copy of the recipes you've got. I'll shoot an email your way. As for the KCL causing pits and such, I'm almost 100% certain that's not an issue. It's "almost" since I haven't yet fired mine up to see, but know of a few folks who have used them for some time and have had no issues in that way. Again, thanks for the insights.

Jeremy
 
You must log in or register to reply here.
Back
Top