Brine Quench Revisited...

69_knives

69_knives

Joined
Nov 20, 2008
Messages
1,855
Just going off a couple of tidbits gleaned from a recent quench thread...

There were a couple of references posted that suggested that a higher than optimum salt concentration produces a slower quench medium. So, my question is this; if the optimum salt solution of 5-10% salt by weight in water is too severe for certain steels could the severity be successfully be lowered by increasing the salt concentration.

I guess the answer depends on whether or not increasing the salt concentration causes anything else to happen besides slowing down the quench.

Thoughts? Or is there already existing data relating to varying salt concentration quenchants?
 
I always thought of it as a sort of bell curve the quench speed increases as salt % increases to a point 8%-10% by weight, then decreases as more salt is added. so yes I reckon it could, but if a brine is too severe you could also reduce the speed by lowering it or removing the salt entierly
 
I thought the issue with water was not that it is slower but plain water causes an uneven quench because of steam pockets and where it is actually touching the steel it is faster than brine, Causing the dreaded warpage and cracking.
 
good point, I had not considered that. I do think that because of the vapor jacket in water is undesterbed it is slower, but upon colaps more volatile, possibly resulting, in warpage. so her's another point why salt?
I think the principle reason salt works to destabilize the vapor jacket is that the dissolved salt somehow prevent the vaporization stage from lasting so long (the boiling point of salt water is higher than 100 C)
so this could be achieved by other salts not just NaCl, and thus probably by any solute, I've heard that dish soap can work well in this capacity
 
Just an update on this; I mixed up a brine solution with a recipe of 4 liters tap water (US gallon is 3.78 L) and mixed in 3 LB of water softener salt. I put the mix into a pot, heated and stirred the water to dissolve the salt, not all of it dissolved, a few chunks were left on the bottom.

I quenched one small, 1/8" thick 1084 folder blade with an edge thickness of about 0.010" and finished to 150 grit. The blade came out clean and hard, a slight bit of scale residue easily rubbed off with my fingers. So far, so good!
 
Nebulae said:
good point, I had not considered that. I do think that because of the vapor jacket in water is undesterbed it is slower, but upon colaps more volatile, possibly resulting, in warpage. so her's another point why salt?
I think the principle reason salt works to destabilize the vapor jacket is that the dissolved salt somehow prevent the vaporization stage from lasting so long (the boiling point of salt water is higher than 100 C)
so this could be achieved by other salts not just NaCl, and thus probably by any solute, I've heard that dish soap can work well in this capacity
Click to expand...
salt raises the boiling point of water, hence more heat absorbed before phase change, and salt creates nucleation sites for steam bubbles so instead of big bubbles you get many very small bubbles, and it changes the surface tension to act a bit "wetter" If you add dish soap to brine you get what is called "SuperQuench" which is such a severe quench it will make water hardening steels crack

-Page
 
The confusion comes in the wording used. Brine quenchant is most effective at 5-7%. It is less effective above and below that concentration.....not actually less severe. As you figured out it may have some problems in doing what it is supposed to do if the concentration is wrong.

Now, that said, brine quenchant is only necessary for a couple reasons in knife making:
1) To harden the most shallow hardening hyper-eutectoid steels- W1/W2,1095 - usually in thicker sections.(The eutectoid 10XX series- 1070,1075,1080/1084 - have enough hardenability to use fast oil in nearly all circumstances. )
2) To differentially harden shallow hardening steels, usually to attain a hamon.
3) Because it is cheap and easily obtained.
4) To obtain sori (and hamon) on Japanese long blades .
5) To say, "I did a brine quench, and my blade didn't crack."

Stacy
 
LoL that could be a good Knife makers MasterCard commercial.

5) To say, "I did a brine quench, and my blade didn't crack." PRICELESS
 
From what I recall from the texts that were posted in the other thread it was a slower / less severe quench, it didn't mention anything about being less effective. I tried it because my equipment is stored at outside ambient temperature and I don't need to heat up 5 gallons of Houghto Quench to quench a 3" folder blade. Water I can store inside the house. I guess if less effective means slowing down a quench to a point where thin cross sections cool at the correct rate so as not to crack or distort your steel in the quench then let's call it less effective.
 
Actually, this is the text I was referring to... If I am reading and comprehending the second exerpt correctly, to me it says you can slow down a brine quench by raising the concentration of salt.

K R Johnson said:
I'm quoting from the book "Tool Steel Simplified" by Frank R. Palmer and George V. Luerssen and published by the Carpenter Steel Co.

This is scanned from page 252:

Brine-1.jpg

And page 254:

Brine001-1.jpg
Click to expand...
 
Good question! Could it be that in high concentrations of salt it becomes corrosive? Just guessing here. You have a valid point. I'd like to know the answer if any one knows?
 
I started this thread to see if and find out for myself if there is a safe, acceptable alternative to the proper quench oils that seem to be unobtanium for many folks or simply not an expense somebody just getting started wants to undertake to make one or two blades and find out it's not for them. If there is evidence that a higher concentration salt brine is suitable for quenching, gets steel hard and doesn't distort or crack your blades I think it is worth exploring, not just by myself but anybody that is presented with the information that is freely available. What I didn't post this thread for was to be looked down the nose of those standing on their pedestal who think their way of doing something is the only way it can be correctly done. I'm sure some of the cavemen stood in the opening to their caves and grunted to the other cave people the proper way to wield their stone to their hot meteorite chunks to form it into a knife but eventually, one of the other cavemen figured out that you could form the meteorite into a hammer and anvil.

Warning:
This post is hype free and may cause free thinking individuals to experiment, explore and hopefully make knives.
 
Whens the last time a caveman bought a knife;)

I'm sure there's "unsuitable", "suitable", and an "optimal" way to do things ( if you don't like the words better or best)

a commercial quenchant made for a specific type of steel being "optimal"
 
Rusty McDonald said:
Good question! Could it be that in high concentrations of salt it becomes corrosive? Just guessing here. You have a valid point. I'd like to know the answer if any one knows?
Click to expand...

From the only blade I've done with this high concentration brine the blade came out really clean, no pitting, no scale. A little touch up on the belt and polishing wheel and sharpening and it looks good.

Anyway, here is the blade:

Gedc0437.jpg
 
it seems very likely too me that adding salt in excess of 8% or whatever the optimal % is will slow the quench, and make it less severe, in so doing puting it somewhere in between oil and water, but more practical, But does anybody actually have data, or any experience doing this
 
Last edited:
I imagine there might be some very limited data on a dusty shelf somewhere but once the researchers found the optimal fastest quench for industry standard thick cross sections of shallow hardening steels they closed the books on anything higher than what they found to be optimal. For the cross sections we deal with in knifemaking there probably isn't a lot of data. I want to do some more experimenting with some test blades but that will have to wait till I get an opportunity to do some forging.
 
Something to think about when considering oil and water:

Oil can frequently quench nearly as quickly as water at and above the nose if it has good vapor control. As I understand it, the primary advantage to oil is the lower heat transfer during the conduction part of the quench when the liquid makes direct contact with the steel. This is also the temperature range when martensite is forming (under 500). There is a sudden dimensional growth during the conversion into martensite because it is less dense. The % martensite follows a line as the temperature drops. If you can slow the rate of cooling at this point, you can allow all the areas of the blade to "catch up" and fall through the conversion at closer to the same rate. It is my understanding that it is the difference in martensite formation (and thus volume) that leads to warping and possibly breaking during a quench, and that is the reason oil has an advantage to water, it is slow in that range.

With that thought in mind, how will the salt effect the conduction phase of the quench? My guess is a high concentration of salt might reduce conduction some, and therefore give temps a bit more time to equalize, but probably not to the extent of an oil. But I don't know.
 
You must log in or register to reply here.
Back
Top