Molten Salt Heat Treating

Laredo7mm

Laredo7mm

Joined
Jul 8, 2002
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Hey all, I spent last night reading about heat treating with variuos kinds of molten salt. It looks like a good way to go for the following reasons:

1) You can control the temp acurately
2) The salt is cheap.
3) The set up would not be too bad to build
4) Little or no oxidation takes place
5) Barium free salts do not decarburize the steel

Do any of you do the hot salt ht? What should I be carefull of, well besides the obvious? I read on Fogg's website that he uses a SS tank to hold the molten salt, is this the way to go or should I get a more exotic alloy like inconel (super expensive)?

Any advice or input you might have would be greatly appreciated.

TIA
 
Be sure you have a good hold on the blade when you put it in! Bill Herndon told me it isn't fun trying to fish a blade out of 1500 degree molten salt! :eek:
 
I use one for sword work, I love it. I think its a good way to go, makes things real easy.
Temp is controlled very simply, I have a digital controller on mine.
I use a mix of sodium chloride(yep table or horse salts) and calcium chloride(an ice melting salt) both are gotten simply and cheaply.
Realatively easy to build, a small knife size setup would be very easy IMO.
keep the salts clean and replace them occasionally and theres no oxidation or decarb.

You need a good stainless tube for the salts. 316 stainless is great, theres better to be had but way pricey, and not really needed. Your welds(on the cap, to seal the bottom) have to be of the same material, or they will fail easily.

They are dangerous, keep an eye on them, and dont be a dummy.;) (... thats harder than it seems, hehehe)

Joe
 
I checked with my favorite scrap yard and they have some 4 inch OD ss pipe with 1/8 wall thickness. It is type 347, which from what I have read, should be a little better than 316. The difference being a bit more Cr and Ni. Which I would think would make it more resistant to heat and corrosion.

Do you all think that would be thick enough? The price is right too at $1 a pound.

Let me know.

Thanks again for your help.
 
I completed my digitally controlled salt rig back in November, and in my opinion it's the only way to go.

My first round I got a 312 ss pipe from a mill-right that he welded. That was a mistake, he didn't weld it perfectly and it developed a leak last month. Two days after I'd realized it had leaked, EVERYTHING steel in my shop that didn't have paint or oil on it had a nice brown oxidation on it. That stuff is nasty if it burns in the flame.

I got a new 316 tube and am having a friend TIG weld it for me. I wouldn't go with anything thinner than 1/4" I think thicker is even better. Inconnel would be awesome, but very very expensive unless you found some crazy deal on a piece at a scrap yard.

Mine is nice because it is totally self-contained. I built a small cart with casters, and the blower is mounted under that. The forge body sits on top. My quick shut-off and needle valve and fan switch are all mounted on a face plate in the front. I built a small box that the digital controller is mounted in so that it's very close yet protected from both the heat and the salt.

It's very accurate, it holds temp within +/- 3 degrees.

I went to all of the trouble to build the thing, I wanted to make sure I used salt that was made for heat-treating. I think Heat-Bath's "Nu-Sal" and Houghton's high temp are both very good. Maybe they aren't necessary, but I figured why take the chance?

I clean my blades very carefully and make sure they are DRY. Any moisture introduced into molten salt will immediately evaporate and need somewhere to escape to...so it blows salt out. I even put clay coated blades down in the salt, BUT I put them in the oven at 400-500 degrees for 1-2 hours to first make SURE they're dry.

The simplest thing to do is drill a small hole in the tang and put a piece of construction wire through it to hold the blade while in the salt.

Salt baths are nothing new. They've been in the industrial heat-treating scene for years...in fact most industrial places have phased them out. They are a relatively new idea to many knifemakers, but are a fantastic tool...for bladesmithing they are the cat's meow. You can have absolute consistency with much more confidence in your work, I know I do.

Let us know when you have more questions :)
Nick
 
Originally posted by NickWheeler
I wouldn't go with anything thinner than 1/4" I think thicker is even better.
Click to expand...
Yep, I second that, no less than 1/4", for a couple of reasons, the corrosion and in case the pressure ever built up, in bad places(ie: not heated properly) it wont explode as easy.

Joe
 
can anyone show some pictures/examples of what a homemade salt bath looks like?

any links? this sounds incredibly interesting. but i have some questions...

how does it get to such a high temp?

where do you get the controllers for them?

approx how much do they cost to build?

thanks
 
Just wanted to let you know that Kevin Cashen talks a lot about his salt treating pots, and several huge advantages for blades heat treated this way. It's in a LONG thread chock full of LOTS of other great bladesmithing info. Check it out!

bladesmithing secrets revealed!
 
hmmm...according to that, Kevin heats the O1 to critical in a high temp salt bath, then quenches in a 400 degree salt bath. no oil quench at all.
 
Nick,

Thanks for the detailed post. A couple of questions:

1. Any chance you could post some pics?

2. Any chance I could visit for a salt rig building/blade forging session once I move back to CA? Perhaps after the 2004 Oregon show?

Hope to see you soon either way,

John
 
I wish I could use salt bath in my electric Even Heat. Any ideas out there? There is no way I can afford a comercial salt pot (is that what they call it?). I read the posts and it reads like you guys are using the container in a forge.

Roger
 
Hey John, sure! :) Are you coming to Eugene next month? Hope to see you there.

A salt bath really is not too expensive to build...when you look at the control you get for the cost.

Most guys are thrifty and find things on ebay. I found controllers that would work, but I ended up buying a "package" from South Eastern Heaters because Don Fogg had proven it would work, and I got a guarantee that the controller would work that way (no "as-is" purchase).

I made mine fancier than a lot of guys, but that's just the neat-freak in me coming out.

Here's a cost-break down on mine.

ss tube for salt- traded a hunter for them, but as mentioned above was not wise on my part.

NEW 316 ss tube- $50
Salt- I bought about $75 worth (that's extra)
Most of the stucture was scrap stuff I had laying around or bought as such (scrap).
Plumbing parts- about $40-50 (a little much because of how I built mine).
Digital controller/thermocouple/Quencharc supressor- $250
ITC-100 to coat liner- $25
Got the Kao-wool liner from a friend for free
Casters- $15
Blower- I got it for free (it's about $90 from Granger I think)
Ext. cord I used to wire it with- $5
Two cans of black paint- $10

My biggest cost was taking the time to figure out how it would work and go together. I wanted mine self-contained, comfortable to use, and small enough to stow away in the only space I had left in the shop for it. So if you add it all up and the gas I spent running around buying parts... I'd be looking at about $500. That's not counting the $250 knife I traded :eek:

While that's a lot of $$$ for a poor knifemaker like myself, it's a small price to pay for the control and accuracy I now have.

I don't have any pictures of it, but if I can get some I'll post them.

Nick
 
For anyone interested, I have contacted SEHeaters for the controller Don Fogg mentions on his website, will be happy to pass the info along.

Dave
 
Hey guys, thanks for the input.

Dave can you email me that info or post it here?

I got my tube yesterday. It is 3.5 OD wit a 3/8 inch wall and about 15 inches long. Had my tech here at work TIG'd the cap on it. Not bad so far I have only spent $18 on material.

Only one bad thing happend when I was cutting out the circle for the cap. The band saw decided to pick a fight with my finger and the band saw won :mad: Not bad though, about 3/16 deep into the finger nail. No pain, just scared the poop out of me :D The worst part is it is going to cripple my grinding for a while, hey maybe it will improve...lol

I need to do some shopping on eBay for a controller. I have one on my HT oven that I am going to use on the salt bath. It is just an on/off type, so I am looking for a ramp/soak one to use on the ht oven.

I will probably go with Nu-Sal also, there is a distributor here in MI, so shipping shouldnt be too bad. Unfortunately they are going to make me buy 100 pounds of it. I guess i will have some extra.

Anyway thanks again for your help.
 
Just from the viewpoint of a welder guys. I reccomend using a standard weld on type pipe cap for tubes like this rather than cutting one out of plate. The cap will allow you to get a better weld, easier than using plate.
 
Has anyone tried using electric? I've been thinking of making one with electric kiln parts but I don't know if the elements will heat that much mass. basic on/off controller and elements are cheap.
 
Resurrecting an old thread here but I am wondering who sells molten salt for heat treating these days. Did a search and very few results came up.
 
Not sure this helps but there was only one or two places that sold the salts with out buying a 55 gallon drum of them. I would try and email or phone Kelly Cupples at High temperature Tools and refractory. I know he used to sell smaller amounts. Also Nick Wheeler may know where they can be found now a days.

Brett Mathews
Esteem Grinders
 
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