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I'd be interested in learning the pros and cons of tempering to about 400 degrees  Fahrenheit  by immersing the work in a pot of heated oil. 

You could measue the temperature of the oil with a deep frying thermometer of maybe a thermocouple . 

There are plenty of oils (peanut oil, soybean oil, etc.) with smoke points higher than 400 degrees. 

Thanks

 

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A friend of mine was doing that using a PID controller to keep the oil at temperature. He has since moved to a salt bath. I think that he is using bluing salts

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I was having the same question and found your post here. I did a search on the flash points of different liquids. Found two that may be suitable but at least one that I think could actually work. Would be great for people like me who could just heat a small pot with a thermometer for tempering. No oven. 

Guess which one :)

Glycerin - celsius 290 / fahrenheit 554

Linseed Oil - celsius 287 / fahrenheit 548

Source:  http://www.engineeringtoolbox.com/boiling-points-fluids-gases-d_155.html

 

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Watch out for pre-flash vapourization and BOOM!  I like to use tempering tongs and so do a differential temper.  They are tongs with heavy crossbars on the tips of the jaws: to use you heat them in the forge and grab the spine of the blade and let the heat travel making for a softer spine and a harder edge---as you quench in water when the edge is the correct colour. I even found a pair at the fleamarket once...

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I tempered swords in mar quenching oil for a long time, but I have had the oil bubble up and empty its self a couple of times now and i no longer do it. The advantages are even heat distribution. but 450C oil is terribly dangerous and any unheated oil or water droplets turn it nasty quickly.

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W.W.N.,

The price of glycerin may be prohibitive. Unless you live by, and have access to a fish processing plant. (a possibility in Kerala).

Have you checked out the properties of peanut oil? It has a high flash point.

Also, thank you for the engineering reference above.

SLAG.

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Nah, glycerin is a commonly used substance worldwide.  It goes into pharmaceuticals, paint, resins, explosives, cellophane, cosmetics, sausage casings, Pop Tarts, pet foods etc. etc.  We haul it on a regular basis at 45,000 lbs per load. I guess that doesn't mean you can easily obtain it in consumer level quantities though.

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Glycerin is a by-product of making bio-diesel from waste oils and fats. If you could find someone doing that it may be a source. Also suppliers for soap making. I haven't had a reason to look for it, so I don't know about availability and quantity.

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Why let oil smoke at all? Put a cover on it and purge the air with your mig welder's shielding gas, even 75/25 it doesn't need to be inert just displace the oxygen. Oh heck a piece of dry ice or puff from a CO2 fire extinguisher will work. Open the valve so there's positive pressure in the tank, open the cap, slip the piece(s) to be tempered through a curtain, close the cap and set the timer.

Frosty The Lucky.

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In bulk I got it from a website called bulk apothecary.  Of course that was after really odd questions at the pharmacy about why I needed it by the gallon...  And the price was vastly cheaper.

 

 

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This from Tom Bredlow years ago.

 

When tempering small springs, anneal, harden, then flash them in corn oil once or twice. According to him the flashpoint of corn oil is what makes a good temper for springs out of 10xx or W1 tool steel.

Works for me

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