Heat treating a ladder pattern damascus fixed blade with a molten salt bath. L6 and 1095 steel. 1st quench from 1650F, 3 more quenches from 1450F.
[01/21/2019] I'm adding details from a reply on a previous comment with some editing. I apologize for not adding much information where it was not easily accessible. I did not expect this to get as many views as it did, and I haven't really been checking. Frankly, bladesmithing has been an on and off hobby for me (mostly off) for over 20 years, and I haven't done much since the video. I've also moved since the video was made, and I need to get a shop set up again.
Here is the information from the comment (with editing):
I'm using a CN7500 controller from Omega Engineering (it's clamped to the anvil in the video), a gas valve (alcon 29BZ135C3-1EDH), and a stainless steel sheathed thermocouple to control the temperature of the salt. In steady-state, it won't vary more than 1F. The temperature dips when you put cold steel into it, but the controller doesn't overshoot as it comes up to temperature. I should note that I ran the controller's auto tune sequence BEFORE putting the steel in--to make sure the control was tuned for this setup.
It's been about 7 years since I first built this (as of video posting date), so I don't remember all the details. I remember doing a lot of research online, but I also saw one in operation at a demonstration. I recommend that you look at a lot of different designs, articles, etc to get more familiar with heat treating using molten salts before attempting to build one. It did take a little time, but it was fairly easy to build.
The inside of the pipe is lined with Koawool and coated with ITC100 coating to help reflect heat and keep fibers in place. The salt pot is stainless steel, and I had that welded with a stainless welding rig to help ensure resistance to corrosion. Even so, the salt pot will corrode a lot.
Be very careful around the molten salt. The first time I ran this, I cooled the thermocouple down with water so I could adjust where the bend was for going into the salt pot. I wiped off the water and stuck it back into the pot, and a second later the salt EXPLODED. I was lucky enough that my head or any other part of me was not over the pot because it shot 1/2 the pot of molten salt up at the ceiling and sounded like a shotgun.
Plan for the case where the salt pot develops a leak. I expect that if the molten salt gets onto anything like concrete, it could cause an explosion, too. You probably should have a metal catch pan under the whole setup just in case. Also, I never leave this setup unattended--just in case.
Also, keep in mind that heat treating salt can decarburize steel. I've seen recommendations of stirring the pot with a graphite rod to help prevent that. I actually crushed some coal into small chunks and let them sit at the top of the salt. I don't have problems with decarb now.
There may be lots of good references on heat treating steel, but I liked John Verhoeven's book Steel Metallurgy for the Non-metallurgist.
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