Animal/vegetable oil for quenching

[Marc]

I asked my local fried seafood place if I could get some of their discarded frying oil. That's not a problem for them, but the owner said that he uses an animal/vegetable oil. Would that present any problems as a quenchant? I'm most concerned with the oil going bad over time. Does the animal part of it get "ripe"?

I'll only be using this on occasional junkyard steels, like 4140 and 5160 (or whatever crosses my path), for hammers, treadle hammer tools, etc.

--Marc

[ThomasPowers]

Both parts can get rancid. Commercial oils often have treatments to prolong their life, but I'd suggest making the tank so it can be dumped/cleaned when it starts going off...

Thomas

[Marc]

Thanks, Thomas. How big a tank would I need for the occasional 3-lb hammer head? I was thinking of just going with a popcorn can.

[Glenn]

A 3# red hot hammer head in a small amount of oil is an invitation for a flash fire. Use a metal container that has a lid that closes and that can put out a fire. A fire extingusher needs to be handy, as well as a cell phone with the speed dial set to 911 (the emergency response). You may not need any of the above but just in case .......

Play safe.

[Ellen]

I like to do my oil quenches outside my shop. Just in case. In a nice bare sandy area I have there. With fire extinguisher and lid, too. Burning oil can be horrific, esp. if it escapes the container and flows across the floor.

I have a 8" square piece of heavy walled steel tubing about 2 feet high welded to a steel base I use for holding the oil.

I also use soybean oil, which has a very high flash point. 35# at Sam's Club for $13. That's almost 5 gallons.

[Woody]

I have a 6 gallon can with about 5 gallons of used oil from a fast food restaruant. I have had it for 3 years and it isn't rancid yet. I do my quenching outside and keep the lid handy in case of a fire. I also keep my hands and other body parts off to the side of the can when I am quenching for the same reason. The only drawback I have found from using oil from a seafood place to quench blades is that every time I draw my knife, every cat in the neighborhood shows up.

Woody

[B. Norris]

Here is my oil quenching tank. I saw this on a bladesmiths site while surfing and cannot remember who, anyway, thought it was a great idea so I used it! The jug holds nine gallons of peanut oil, it will take a lot to get it to flash, and if it does... The lid is airtight. The whole thing fits on a turkey fryer, making preheating the oil simple. Note: I do not use it where it is shown in the picture, that is just where it gets stored.

[rthibeau]

So is there a consensus on whether vegetable oil or animal oil or motor oil makes a better quenchant?

[Woody]

Richard:

I would think that the viscosity of the oil would be more of a factor than what type of oil it is. The thinner the oil the quicker it will quench the metal. The more viscous oils like 90 weight gear lube would tend to be a slower quench than say a 10 weight oil. A lot of people swear by ATF which is pure petroleum based oil without a lot of addatives. A lot of people advise that you shy away from motor oils because of the addatives that are in them which can have a toxic effect on the body when vaporized by the hot metal. I use used vegetable oil from a fast food joint because it is free and it works for me. You will have to expiriment a little and see what works for you. Take note of exactly what you do and record the conditions that way when you get the desired result, you can duplicte the process.

Woody

[Ed Thomas]

Viscosity, temperature, and composition all play a part in the cooling rate of an oil. If it is an issue in your heat-treating, perhaps you should consider oils designed specifically for oil quenching such as item numbers 3202K1 and 3202K7 in McMaster-Carr. These are the part numbers for a 5-gallon container of normal speed (28-second quench time) and high speed (10-second quench time) respectively.
http://www.mcmaster.com/
You can see that the difference in cooling rate is significant. However, it is a moot point if you don't know your metal composition. Every metal type has a recommended heat-treating chart with guidelines for optimizing that alloy for a particular application. Guessing is usually futile.

For example, here are two pages on M2 steel:
http://www.suppliersonline.com/propertypages/M2.asp
http://www.pvsteel.com/docs/Tsb-118.pdf

Here's an example of the real complexity involved in crystal transformation in heat-treating: http://sb2.epfl.ch/instituts/Gotthardt/Former/Bataillard/Research.html You can see that it is not trivial. If you are a blademaker or machinist, then you pick your alloy, and learn its particular heat-treating demands, including the best quenching composition and temperature.

On this table, http://www.knives.com/heatreat.html you can see at the bottom the relative shock rate of different quenching mediums. It is interesting to note, that the agitation (how fast you move it around while quenching) has a very big impact on the cooling rate. You can see that according to this table, the shock rate of oil is about 1/3 that of water... all other things being equal.

Having said all this, if you are a ornamental blacksmith making ordinary shop tools, then use a clean vegetable oil in a can with a drop-down lid and go forge something. The difference in quenching behavior between oils just isn't significant enough for us.

A can like this: http://www.barcoproducts.com/store/item.asp?ITEM_ID=650&DEPARTMENT_ID=111 with 5 gallons of vegetable oil has done me fine for years. The vegetable oil does not go bad. The lid keeps the bugs and mice out, and the fire in. The foot petal leaves your hands free.

[Hillbillysmith]

Personally, I use water for al mild steel, and vegitable oil for my higher carbon steels. Depends on what I'm making, and the aplication for that specific item, I might quench in cold oil, and leave it alone, or I might quench in oil at an orange heat and then temper in water when it just starts to move colors (light/dark straw to light blue). All I use (in the way of oil) is vegitable oil. I've never had it flash on me (and as I've said, I usually quench at an orange heat) but anything is possible. Plus, I like the smell :)