can we agree to disagree?

[SReynolds]

Two popular smithing books.  Two different opinions on technical information.  I thought technical info is cut and dry. Not opinion. 

So one smith says salt brine cools the work quicker than water. Another says cools slower than water.

I was asking a well known smith a technical question and when I asked him to clearify he replied that I take information too literally.  So I have been thinking about that today.  

What technical information should we take literally and what should we pass off as opinion?

[ThomasPowers]

Sounds like a good HS science fair project. drill 2 pieces of steel and insert thermocouple. Heat to specific temp.

Quench in different quenchants at the same temperature for a set time, say 5-10 seconds and record end temp.

However I'm betting my ASM handbook on heat treating already has a good answer to that question...

[SReynolds]

Probably not to be taken literally.  I would say. 

I had a class of 14 high school students today in which I did a heating demo for the industrial arts class and was cautious to only give technical information and not opinion. 

[Frank Turley]

"Heat Treatment and Properties of Iron and Steel" is a Government Printing Office monograph, 1966, and it says on page 24 that brine Is a faster quench than water.

[ThomasPowers]

What I remember is that it's supposed to be a more *even* quench!

[Kozzy]

The thermal conductivity of salt brines don't vary much from that of water. Depending on a lot of factors (concentration, temperature, pressure), you are speaking .68 for water vs .66 for saturated brine (I won't go into the units used because that doesn't matter for comparison).  So in terms of sucking heat from a part, there is only a roughly 3% difference with water being ever so slightly better (as a liquid).

In terms of boiling point, saturated salt brine boils at about 2 degrees C above pure water at STP.  You get a little benefit there in that you might not produce as much of a thermal steam blanket on the surface of the part but for all intents and purposes, the temp of the part is so high when it hits the solution the difference in the blanket is also nil.

At least by the numbers, salt brine vs water seems to be mostly about perception and not fact.  That explains why you get diametrically opposed answers:  People tend to believe what Grandpa told them.

To clarify, we're talking simple brines, not the fancy solutions which are also often "salts" nor the molten salts often used in commercial heat treating operations.

[SReynolds]

Correct. Simple brine solution.  Apparently the published experts don't agree.

One recommended used engine oil and if you mention that on a Facebook group for blacksmiths, they will all but ban you from the group.

[Will W.]

Well, for what it's worth, oil has a higher boiling point than water, and quenches slower. Brine has a lower boiling point than water. Logically, wouldn't it quench faster?

It's worth noting that this is little more than conjecture. I'm not an expert on the subject. 

[Kozzy]

So...it appears you are delving into the realm of strongly held perceptions on things like brine or the oil you drained from Dad's Cadillac in 1973.  The issue then becomes a lot like politics or religion.

Studies show that when you challenge strongly held belief systems with indisputable fact---people don't change their beliefs to match fact.  Instead, they actually tend to double-down and believe the original (often false) perception even more strongly.  That's part of why it's a waste of time to argue politics with your weird Uncle Ted:  He can't be swayed with any amount of fact and you'll actually make him more of a zealot with your factual challenge.

I'm nothing but a hack smith and fabricator but I have definitely noticed that this perception thing runs deep in the smithing world.  If one's mentor taught one to use only purified cocoanut oil, that's what tends to be held as gospel.  If your mentor told you something about aligning the blade north-south to prevent warpage, gospel again.  The only way to overcome this is by replacing the belief with something clearly better--not just something different.  Human nature makes that darned tough.  Heck, there are still people who swear putting raw meat on a black eye helps it heal.  The best you can do is show them something which helps it clearly heal BETTER and they might...just might...grow to accept the change and abandon the old (but rarely the belief itself).

[JHCC]

33 minutes ago, Kozzy said:

In terms of boiling point, saturated salt brine boils at about 2 degrees C above pure water at STP.

STP = Standard Temperature and Pressure = 0°C (32°F, 273.15°K) and 1 Atm (101.3kPa, 760 mmHg, or "sea level"). Neither water nor brine boils at STP; I think you were referring to Standard Pressure.

[Kozzy]

1 minute ago, JHCC said:

STP = Standard Temperature and Pressure = 0°C (32°F, 273.15°K) and 1 Atm (101.3kPa, 760 mmHg, or "sea level"). Neither water nor brine boils at STP; I think you were referring to Standard Pressure.

oops--typing too quickly.  I was just trying to avoid the "But what about in Denver?" issue and not get into the technical swamp of other exceptions to the rule. 

[Will W.]

I concede your point. 

Thinking this through, adding salt does in fact raise the boiling temp of water (that's why it's added to pots of water when cooking) and lowers it's melting point (that's why it's added to icy roads.)

I was mistaken. For some reason, I thought it was reversed. Disregard my last post.

[Alan Evans]

I hesitate to enter this erudite fray...but is not the vigorous movement, or otherwise, of the workpiece in the quenchant likely to have a greater effect than the salt content or the boiling point of said quenchant at whatever altitude?

I understood that the constant movement (and/or constant supply) of fresh quenchant in contact with the workpiece prevented, or at least helped to reduce, the formation of the steam blanket...or is this another of weird Uncle Ted's ideas?

Alan

 

[Andrew Martin]

Yeah, I always wondered about that inconsistency( it's even specifically pointed out in Mcraven's The Blacksmith's Craft) until I did a little extra reading. After reading a few different HS metallurgy textbooks and Dr. Verhoeven's Steel Metallurgy for the Non-metallurgist, it seems the scientific consensus is that simple brine is faster than water is faster than oil. 

Alan, Verhoeven does say agitation reduces the steam blanket significantly, but I can't remember if it has more or less effect than salt concentration in water quenches. 

[JHCC]

Wouldn't the speed of the quenchant and the effect of agitation be independent of each other? It's not an either/or proposition: you could agitate your workpiece or not, regardless of what you're quenching it in, no?

[Alan Evans]

Absolutely.

Maybe the agitation just enables the quenchant to work at its optimum rate....maybe agitation is the norm and gives the constant property of the coolant and leaving the object static yields a more variable outcome.

I suppose I have read it somewhere, but I think my understanding was that it could overlap the effects...for example, agitating a similar object in water could be faster than no agitation in brine. Even though like for like, brine would be faster.

Probably the relationship of volume to surface area is more likely to affect the outcome as well. A thin flat like a knife blade relative to a larger cylindrical form like a Ø50mm (Ø2") punch and drift.

Lots of interdependence, lots of variables....

Alan

[JHCC]

2 hours ago, Andrew Martin said:

Verhoeven does say agitation reduces the steam blanket significantly, but I can't remember if it has more or less effect than salt concentration in water quenches. 

I suspect that since critical temperature of the steel is higher than the boiling points of water, brine, and oil, you're going to get some degree of leidenfrost effect regardless. (I suspect that that degree would depend at least in part on the viscosity of the quenchant, which would at least partly explain why one preheats quenching oil.) Agitation will break the steam jacket and allow the quenchant more constant contact with the workpiece, at which point differences in thermal conductivity comes into play. 

This is just me thinking out loud, though; I make NO claims of being a metallurgist!

[Alan Evans]

Google is our friend...here is a screen grab from page 125 of the very book with the very topic!

I had remembered the agitation effect correctly...that is a relief!

Alan

Steel Metallurgy for the Non-metallurgist

 

Edited February 23, 2017 by Alan Evans
to make it less confusing

[AnBello]

1 hour ago, Alan Evans said:

(...)

Lots of interdependence, lots of variables....

Alan

Actually, we are very lucky that these variables are pretty much independent, and not so much interdependent (for simple calculations). It can be simplified enough to consider each variable by itself, and add the results later, and still be close to the real result. This makes it a lot easier, since oil is slower than water, and agitated oil is still slower than agitated water.

Imagine having enough non-linearities to make still oil slower than still water, but Agitated Oil faster than Agitated water, for example. Now that would be ugly.

And I am really interested in this topic, since I had always assumed without questioning that brine was faster, just because I've seen it in posts here over and over again. To actually challenge this (and get to a final statement) is quite important, in my opinion. Can I keep my belief (backed by facts now), or is this still in doubt?

[Gerald Boggs]

15 hours ago, SReynolds said:

Two popular smithing books.  Two different opinions on technical information.  I thought technical info is cut and dry. Not opinion. 

So one smith says salt brine cools the work quicker than water. Another says cools slower than water.

I was asking a well known smith a technical question and when I asked him to clearify he replied that I take information too literally.  So I have been thinking about that today.  

What technical information should we take literally and what should we pass off as opinion?

The problem is not differences in opinion, but rather differences in knowledge.  One smith can be quite knowledgeable and the other just a good talking.  If one wants to understand something, one should go to the reference material.  In this case a textbook on metallurgy, not only will the answer be there, the why will also be there.

[Gerald Boggs]

9 hours ago, Andres Bello said:

And I am really interested in this topic, since I had always assumed without questioning that brine was faster, just because I've seen it in posts here over and over again. To actually challenge this (and get to a final statement) is quite important, in my opinion. Can I keep my belief (backed by facts now), or is this still in doubt?

This is my favorite book for first time readers of  metallurgy, "Metallurgy fundamentals" by Daniel A. Brandt.  It's an easy read, but still covers the subject quite well.  Copies of it are in all four of my local libraries so I'm guessing it's an easy find in the US, but Argentina might be a different story.

 

[Latticino]

There is an interesting, relevant, excerpt from the 1914 Machinery's Handbook (page 1132):  http://www.woodworkslibrary.com/repository/machinery_handbook_for_machine_shop_and_drafting_room_1914.pdf

It substantiates the brine solution/faster than water/faster than oil under typical conditions.  This book was published when on site heat treatment was a more common part of a machinist's job and I would tend to believe it.  My personal theory is that the elevated boiling point of brine has a lot to do with the difference as in an agitated bath (as recommended by most heat treat manuals I've scanned) the local vaporization of the quench media near the stock would be delayed longer.  I can see this allowing better heat transfer.

[Alan Evans]

2 hours ago, Gerald Boggs said:

The problem is not differences in opinion, but rather differences in knowledge.  One smith can be quite knowledgeable and the other just a good talking.  If one wants to understand something, one should go to the reference material.  In this case a textbook on metallurgy, not only will the answer be there, the why will also be there.

It is all fraught with danger though...people that write reference books are not always practicing or practical people. They make mistakes. I even know of two well respected practitioners in this field that have made mistakes when it came to putting their knowledge in print.

I agree though it is the best we have got.

Alan

[SLAG]

Lat.

The u.r.l. produced a blank page when I tried it. Has it worked for others?

SLAG.

[BeaverNZ]

I remember when in one of my apperenticeship classes thousands of years ago the tutor stating that brine has a faster qench because a saturated solution is alcaline and helps remove the scale from the surface of the item aiding the cooling rate. I wonder if any one has any borderline carbon steel that will only partially harden and try both and see what works better