Hot Bluing Tank

indian george

indian george

Joined
Feb 15, 1999
Messages
11,566
I was told that I could harden a blade in my tank. Has anyone tried this, at what temp and how long??
 
IG, It has been a while since I have done any hot blueing but those salts only between 295 - 305 to blue steel. I don't think those burners will get hot enough to do anything more than temper a blade.

Matt
 
Hey George, this is exactly what a lot of makers who use salt pots do. I'm thinking on setting up a salt pot eventually and also a low temp pot. As a quenching medium the low temperature bluing salts can be used for marquenching at around 400 degrees F. When the temperature of the austenitized blade stabilizes at the temp of the quench it can be taken out and allowed to cool in air at which point the martensite forms. The martensite doesn't form in the quench but the steel has the promise to harden. By all accounts the martensite formed is much more durable and less brittle than normally quenched blades. I've heard that Kevin Cashen ( I think it was Kevin?) at demos will harden a blade this way and then drop it point first on the floor before tempering with no damage to the blade. An added plus is that you can then stick the blade back into the low temp salt for tempering. The process would probably need to be adjusted according to the steel used but I know for sure it works great with L6.

Blades can also be straightened by hand right out of the quench before the martensite sets up. I imagine the window for doing this is pretty narrow, if I remmeber right the martensite will form by 200 degrees F or so.
 
I have an old machinist's handbook that lists a hot salt bath as a method for fast tempering, something like 10-15 minutes for tool steels. Temperatures are almost double the normal draw times, if I remember right. It says that its not as consistent or effective as the normal 2 hour cycles so I didn't give it much thought. I can post the specifics here if anyone is interested. It might be good for steel fittings like gaurds and stuff that you want to harden.
 
Hmmm...there may some confusion here. To answer your question directly George, no you cannot use the bluing tank to harden steel (I think you already knew that.)

Heated to around 400 degrees F these low temp bluing salts CAN be used as a quench AND they can be used to temper hardened steel.

So the process would be heat your steel in a forge or salt pot, lets say to 1500 to 1550 degrees F, and then quench in the 400 degree F or so salts, agitating the blade some in the salt, withdraw the blade when it reaches the temperature of the salt and allow the blade to cool the rest of the way in air (this is when the blade hardens), then put the blade back in the salt to temper, pretty nifty hmm.

I think Bruce Bump and Nick Wheeler have been fooling around with this some.
 
George, I have quenched and tempered in nitre blue salts from Brownells. It seems to work well but isnt as convienent as tempering in an oven. The marquenching allows you to straighten the blade at tempering temps because full hardness isnt completed until the blade reaches about 150f. This is very handy if the blade has some remaining stress. I have been using Nu-Sol heat treating salt lately and quenching in texaco A and tempering in the house oven. Works for me.
 
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