How much oil is not enough oil?

[Allomancer Jak]

Is there a proportion of oil to steel as to how much oil to use when quenching? I just want to make sure I will be using enough, since I've never made knives on my own before. If I don't use enough, will the oil get too hot and not harden the steel?

[John McPherson]

Oh no, much worse! The superheated oil will burn like a torch once it reaches the flash point, and boil over turning your floor into a lake of fire. Turkey Fryer fires ring any alarm bells?

 Also, when you pull a blade out too soon, the smoke can ignite, giving you a tower of flame. Right in your face and up into the rafters.

I cringe *every* *single*  *time* I see someone quench a blade inside a wooden building on video.  Do it outside, in grass or on gravel. Keep a lid handy, and a big fire extinguisher. Water just spreads the flame.

[Allomancer Jak]

I appreciate the warning, but I'm still not clear on my initial question. Is there a minimum amount of oil I need?

[Frosty]

You need to be a little more specific for a specific answer. I know it doesn't sound vague but there are a couple details that make all the difference. 

What kind of oil are you going to buy? What size blades do you want to make? The size of the blade is probably the most significant factor. I don't make blades but do harden steel on occasion, I wouldn't have less that 5gl. for steel weighing up to maybe 4-5 oz. Bowies, seax and up will want a larger quantity though if you're using purpose made quench or heat transfer oil 5gl. might be enough.

My quench tank is a 15gl. grease barrel with the lid and a piece of 1/4" (maybe) plate laying on the bottom for puncture protection and it's sitting in a cut down 55gl. drum again with lid. I rarely have 10gl. of oil in it. The lids are fire snuffers, the larger drum  is boil over protection. Outside is good but cleaning up an oil spill can be a serious job of work. If you''re going to do a lot of oil hardening you might want to think about taking oil spill containment precautions. It doesn't need to be fancy a sheet of ply wood covered with sand makes shoveling up contaminated sand easy. I like my overbarrel better, it's as easy to clean up as it gets. Whatever you do spills are worth thinking about.

Iforge has a pretty extensive heat treat section there may be specific info there. 

Frosty The Lucky.

 

[ThomasPowers]

Yes you need "enough"!  Factors in calculating this is size of the blade---you want to have "room" all around the blade to let oil convection cells flow freely.  You want enough oil that it can absorb the heat without overheating.  You want enough oil that if you are quenching multiple pieces it doesn't overheat (Knifemakers often heat treat multiple blades sequentially at a time. )

If you are doing small blades a gallon may be enough; large blades 5 gallons should do in most cases (and less in others). Swords are a special case indeed!

The ASM handbook I have is not a big help as they refer to large industrial situations with things like "a 800 gallon quench tank"...

[swedefiddle]

Good Morning, Jak

There is not ONE oil that can be used. I have 3 different Quenching Oils, they each quench at different rates, slow to faster. The rate of quench is, How many degrees of heat will be quenched, per second. Different cross-section size of the same material will quench at different rates. A heated piece has the heat to the center of the core, the quenchant will draw the heat from the surface, with the core being the last to cool. The depth that is hardened is the question, typically the core is not hardened.

You need to experiment SAFELY!!!!!! Read all the Heat Treating data on the material you are working with. It is not created lightly.

Neil

[Allomancer Jak]

Thank you all! This is very helpful.

[JHCC]

In addition to the above (which is all excellent information), there is the general rule that you want a minimum of one gallon of oil for each pound of steel, multiplied by the thickness in inches (rounded up). 

Thus, a three-pound workpiece in 1-1/2" steel would require a minimum of six gallons of oil. 

[ThomasPowers]

As stated only a general rule as a 2 pound sword 30 inches long would require 2 gallons using it: 1 gallon x 2 pounds x (1/4" rounded up to 1")  Factors like agitation or cooling systems for the oil can also have an effect.  My quench tank for longer skinny items has thick steel walls which help dissipate heat.  If I regularly do a lot I would probably put cooling fins on it and maybe a fan.

I do use it with a laboratory thermometer after one student of the "more is better" school thought that if warm oil cooled better then hot oil....He couldn't figure out why his blades being quenched in oil hotter than his intended draw temperature were coming out softer than expected...