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Questions on oils and brine


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I've seen different posts where people quench their blades in peanut oil, canola oil, or various other oils onions, or brine.

 

In my shop, I have 8 gallons of used motor oil. I've used to to harden several blades and a few tools and it works, other than the black scale it leaves behind.

 

My question is: Does the type of oil matter? Is vegetable oil versus motor oil any better or worse?

 

Why do we warm the oil up first? If the idea is to cool the steel, wouldn't we want cooler oil?

 

And if a man was to make his own brine, what ratio of water to salt would he need? And would iodized or water softener salt work?

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DIfferent oils act differently.

You can find references that tell how different oils work. There are oils made just for quenching that have specific characteristics. However, vegetable oils have very similar characteristics to commercial quench, the biggest difference is that the commercial oils have additives to reduce them breaking down in use and prevent flashing.

I wouldn't use motor oil. It has different additives and if it's used it may have picked up other things that may not be healthy. (not that the fumes from any oil is going to be good to breath)

Warm oil has a lower viscosity than cold oil, this is why warm oil (to a point) cools faster than cool oil, it moves easier so has greater convection.

 

I don't know about the brine as I haven't used it.

 

ron

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Most any carbon steel will harden in oil. I like vet grade (or food grade) mineral oil. I buy it by the gallon at the feed store. It has a high flash point and doesn't leave much scale.

 

Some steels are made to harden in water (faster than oil) or brine (faster than water) but many steels will self destruct in water. Water increases the stress on the blade by a large amount, over oil. The makers who are good at water quenching lose 1/3rd of their blades in the quench. I've never (knock on wood) lost a blade in an oil quench.

 

Geoff

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Most any carbon steel will harden in oil. I like vet grade (or food grade) mineral oil. I buy it by the gallon at the feed store. It has a high flash point and doesn't leave much scale.

 

Some steels are made to harden in water (faster than oil) or brine (faster than water) but many steels will self destruct in water. Water increases the stress on the blade by a large amount, over oil. The makers who are good at water quenching lose 1/3rd of their blades in the quench. I've never (knock on wood) lost a blade in an oil quench.

 

Geoff

Yes, it really depends on the steel. Steels like 5160 and O1 don't really seem to care what oil you quench them in, while W2 is a bit more picky and needs a very fast oil or brine to reach full hardness.

 

I wouldn't suggest quenching in used motor oil, it gives off hazardous fumes, while quenching in canola oil it smells like I'm baking cookies....:) Regardless, avoid breathing the fumes.

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As for the cold oil, the faster the cooling the more likely to snap from the shock. That's why water is iffy; it cools too quick. I've cracked to blades because the oil I used was too cold.

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Wow, thanks! That helps a lot. I guess I'll have to hit the local feed store fairly soon. I used used motor oil because it's what I had available, and it does stink and smoke something fierce.

 

I had one genius tell me once I should use mercury, since it would cool blades quicker... :blink:

 

Not even going to go near that one.

 

As for brine, I used to be a Culligan man years ago, and the brine in their water softeners is just water totally saturated with salt. If anyone knows a specific ratio, I'd like to know, but other than that, I think I'll just add some rock salt to the water and see what happens.

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Warm oil has a lower viscosity than cold oil, this is why warm oil (to a point) cools faster than cool oil, it moves easier so has greater convection.

This is correct. As a general rule the oil should be heated to about 120 degrees Fahrenheit, though for professional quenching oils go by the manufacturer's recommendation.

 

As far as brine, I've heard 1 cup of salt to one gallon of water... I don't do brine, though, hopefully someone who uses it will clarify...

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Buck,

 

First of all, since you are new to H/T'ing blades I would recommend using a forgiving steel like 1084 or 5160. All steels have a different ideal cooling rate which will determine what to quench in. Many are A LOT more finicky about the quench than these two are. Either of these can be quenched in common cooking oils like canola with good success.

 

A brine quench is much too fast for most steels which will introduce too much stress into the blade and cause cracking on a high percentage of them.

 

There are many threads about the H/T'ing of blades. Do some research before getting very far into making blades. You'll be glad that you did.

 

Gary

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I've spent the last 7 years quenching in various oils and water and brine.

I will suggest after listening to Kevin Cashens talk at Ashokan that I was convinced it was a better idea to buy an industrial quenching oil.

His message was trust industry, they can't afford making bad parts and need consistent results every time.

I have used brine made from regular sea salt and soapy water which I like better.

The soap isn't corrosive to my tongs and quenches really fast.

As far as a quench oil. I bought 5 gallons of Parks AAA which is slower than the #50 and works for everything I've put in it and I have not cracked a blade yet.

I know there has been problems getting Parks but McMaster Carr's 11 second oil is faster than the AAA so it should work for pretty much everything.

I will be testing it at some point.

What I quench in soapy water is material from hearth furnaces. That's all.

The Soap and or Salt reduces the vapor jacket around the work piece and allows it to cool faster.

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I second JJ. The cost of the oil from maxim is very small when you consider you will have the correct speed oil that will if you do your part give you higher RC values. Its not just that they are engineered to get a specific steel below the pearlite nose in time needed they also slow the cooling once below 900.

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My feeling about a brine quench is to only use it when you have a shallow hardening steel that won't harden in oil. I had some 1095 that must have had a low manganese level because I couldn't get it to harden in vegetable oil. I went to brine and it worked fine. I've seen other 1095 steel that did harden in oil so don't assume that all 1095 is the same.

 

Doug

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If you do go for brine and a truly shallow-hardening steel (no scrap), the recommended mix is 8.5 to 10% salt to clean distilled water. Works out to about 3/4 pounds rock salt per gallon.

 

If you want to find a steel that works with that, check the composition. It should be just iron and carbon (between around 0.45% and 1.3%) with a manganese level of less than around 0.4%. Anything else and all bets are off.

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Thanks for all the advice! If I learned anything, it's that I need to learn a lot more about metallurgy (like vocabulary words)!

 

Where I'm still starting out and on a budget, my steel is leaf springs from a truck, and a pair or torsion bars, as well as a few old farrier's rasps. I have no idea what type of steel they are beyond "Spring Steel" and "really hard." I know enough to anneal the rasps before I attempt anything with them.

 

My current projects are a couple of beater swords made from 1/4 inch mild steel. Made just to hack weeds and get a feel for making one than anything else. I used the mild scrap because it was available, and a a way to get familiar with my plasma cutter.

 

I was looking at brine as an option because I can make that. I can probably also snag some olive oil from the kitchen. We use it on our tack, so there's generally a couple of gallons in the pantry.

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Soap encourages (via surface tension modification and nucleation sites mainly) bubble formation --> uneven cooling --> warping/cracking. Don't add soap.

Salt decreases the heat capacity of the the water (increased heat of vaporization is negligible), so it heats up quicker. This makes a quench in brine a little less harsh than straight water.

Oil is great more from the fact that it is more consistent than it is because it is slower. While some bubbling will occur, it is to a much smaller extent than with water. That makes the cooling more even, which in turns makes the stresses in the blade more even. Stresses aren't bad, stress differentials/gradients are what breaks things. That isn't to say it isn't slower and therefore more gentle, it is. Just that that isn't the most important part as far as I can tell.

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Brine might have to wait until summer (an uninsulated shop with a tarp over the door ain't that warm. Running the forge=warm body and cold feet). But I think I will try mineral oil or olive oil on my next quench, first to see what happens, and second, I really don't want to have to grind off a lot of scale if I don't have to.

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