i have a question about the different media used for quenching. as i sit here in the evenings i read a lot. haveing read a few books on blacksmithing and noticed a difference. when discussing quenchants they all list oil as the slowest /least harsh, some then go to water others to brine, with the harshest flipping the water and brine. what is the consensus here as to order of severity of quench media? air - oil - water - brine or is it air - oil - brine - water.
Alright so lets say that a higher boiling point has a slower cooling factor. That is what we're saying right? So on quote from Alexander Weyger's book The Complete Blacksmith, he lists water having a boiling point of 212 F, Brine at 226 F and Oil at 290 F. His claim is that because of this water is the fastest (and harshest). Makes sense to me but is it true? Seems like everybody I've heard from in the groups and forums believes it's the other way around for water and brine. Don't have a particular favorite here myself but I'd like to get straight answer on this one ;-) Granted there are offsets to the boiling points since water boils at different temperatures depending on the altitude (air pressure) but I would think the same holds true for brine and maybe oil too? Then there are a variety of oils in use as a quenching medium so not all oils will work the same (as other oils). Now other sources I've read (think it was Metallurgy Theory and Practice by Dell K. Allen) make the statement that when the quench boils it actually creates an insulating heat shield till the vapor blows off and so would cool less efficiently once that happens. Hey, I'm confused and thats after reading the work of the "experts". Might just be me though...
"Tom Stovall" wrote in message news: snipped-for-privacy@REMOVEwt.net...
Pretty much all competent sources agree on brine being the fastest quench. As for why, think not "boiling point", think "heat capacity", or "specific heat". It takes more heat to heat up the same amount of brine rather than water. More heat for water than oil. Believe in boiling points? Grab a thermos full of liquid nitrogen and try to get a good quench in it - it's not how cold it is, it's how fast it takes the heat away.
Just to add to the confusion I have a book ("what steel shall I use?") that makes a distinction about what temperature the quench material needs to be -- they talk about experiments involving quenching low-carbon steels in chilled brine, and you can certainly chill brine down to a lower temperature than plain old water.
And yes, the boiling point of a liquid is determined by the air pressure
-- you can boil water at room temperature if the pressure is low enough. Lower the pressure even more and you can boil it until it freezes, then watch it sublimate away.
I suspect that there are a lot of factors beyond just boiling point that affect how quickly a quench medium can transport heat away from a piece
-- just off the top of my head the boiling point, thermal capacity, thermal capacity of the medium _and_ it's vapor would all have an effect. Two of my references ("What steel should I use" and "Hardening", or "Hardening Tool Steels" by Linsay press) both make a point of saying that quench water must be clean and one of them ("Hardening") recommends throwing in a bit of lime if the water gets soapy -- I can't see how this would affect any of the qualities that I've dreamed up already, yet obviously _somebody_ believed it made a difference.
Standard disclaimer: This is all just book learning; I've only quenched one or two pieces in my life, so I can't claim to be anything resembling an expert (although I have annealed any number of drill bits without really meaning to :).
I don't know what that mess mixed together will do. :/ It might do just as he sez.
My tool steels book makes a big deal out of the "vapor stage" and how long it hangs on as to the timing and whether it will allow time for the formation of pearlite.
Tap water is quicker than distilled water and adding just 0.2% NaCl made water twice as fast. A "2% soap solution" could slow the distilled water by a factor of 4 which could keep the austenite from decomposing into almost no martensite under certain conditions.
9% solution of NaCl in water was considered the best overall concentration. If you insist;) on using NaOH then 3% is suggested as "optimum".
There's a lot more to this, we've barily scratched the surface. ;)
FWIW, I've had real good luck with commercial quenching oil on 1095 at ~1/32" thick. Beats the heck out of water or brine, IME.
I've heard about the "soap problem" before, but never really investigated it. It's usually put down to some sort of localised foaming problem around the hot metal and a particularly dense layer of steam bubbles. As any text on boilers will tell you, conduction through the metal firebox and the water itself is quite efficient, it's the thin gas layers that represent the real barrier to heat, even though they're so thin.
In this Edge of the Anvil example though, there's a load of wetting agent added as well as the soap. This may well be there to reduce the bubble layer.
I can't think what the original intention of adding soap in the first place is though.
snipped-for-privacy@XX.com wrote in news:crmmgu$coh$ email@example.com:
I have a feeling it could be olive oil or some type of citrus oil, both water soluble. On the subject that started this thread about the soap in the quench, I once had a lady offer to buy some of my quench water right out of the barrel at a show..She said her grandmother, and great grandmother both cured everything by rubbing the water from a blacksmith's quench tank, go figure...Heck if I'd known that to be true, well nevermind..
This is commonly known as Super Quench. It works very nicely on medium or lower carbon steel. Tool steel, properly hardened and tempered is better, but you can get "mild" steel in a much larger variety of shapes.
Here is an email I saved from TheForge. I save many of Hochewa's posts.
To All, Quenchants are to extract heat from the work piece at somewhat of a controlled rate. The traditionally meanest, fastest, ugliest quench was sodium hydroxide (lye) in water to the tune of about 10% by weight. Lye is dangerous as it will chew on your skin, eyes and lungs.
The action of the sodium is reportedly to reduce the solubility of air in the water. Less air, more water better quench.
The action of the salt is to deposit itself on the work piece as the water evaporates around the work. The resulting steam blanket is a poor quench medium. The salt that precipitates onto the surface has some water of hydration in it. As it heats, it turns to steam rapidly (I want to say explosively here but it is not an explosion). This burst of steam breaks down the steam blanket surrounding the work and fresh quench is brought to the surface. The process repeats itself until the work is below 212*F. This is the sizzle that you hear. The formation of steam on the surface of the work extracts a most of the heat. The water does not do much until the work is cool enough that you are not making steam. Then the water cools by conduction.
Common salt in water to the tune of 10% by weight works exactly the same way, almost as well and is a lot safer. The old timers say the brine should be strong enough to float a potato. More salt is not better.
Plain water is not a good quenchant as the chemistry of it is variable. Just imagine what has lived or died or fallen into your slack tub.
MIneral oils can be had in a variety of quench rates. Synthetic quenchants are glycol based and can mirror the mineral oils without the flamability worrys. Motor oils are usually too thick to be effective but they can be used in a pinch.
Gunter's Super Quench is an attempt to maximize the quench rate without the hazards of lye. The principles are the same. The major difference is that the SQ contains surfactants and detergents which are wetting agents. It still contains water and salt. The wetting agents probably do the most good as the work cools to below the flash point of water.
Given all of the above, why do you have to worry about quench rates?
A full explanation of a TTT-Curve is beyond my patience at this point in time. A brief summary follows:
The ttt curve is shaped like a C. The y axis is temperature and the x axis is time. The nose of the C is at or about 1200*f or so. The distance between the y axis at t=0 and the nose of the curve is determined by the alloy content of the work. This also determines the quench. If you go through the nose of the curve you make pearlite. Miss the nose and you have a shot at martensite. For a 1% plain carbon steel like W-1, the distance between the nose of the curve and the y axis is about 1-2 seconds. This means that you must take the work from 1575*F of so to 1200*F in less than 2 seconds. This is why you use brine and this is why it only hardens to a limited depth. For A-2 this time is about 2-3 hours. A-2 is air-hardening. It also hardens all the way through.
Hardening does not occur until you cool the piece to around 400*F. But then this is another story.....