What Difference Does The Quench Water Temperature Make?

yodogsandman

yodogsandman

Well-Known Member
Wondering what difference, if any, the temperature of the quench water makes when oven heat treating? I always try to heat soak the bullets at the highest temperature for maximum hardness. We know that helps but, I've never really considered the temperature of the quench water other than to be as cold as possible. Why am I doing this? Others on other forums have stated that the same hardness levels can come from just using luke warm quench water. I can't seem to find any studies that show one way or another.
 
Brad

Brad

Benevolent Overlord and site owner
Staff member
I have heard that the temp difference between oven and water makes a difference. Some have used ice water to maximize hardness.

I haven't seen any real good tests to prove how much difference it really makes.
 
Rick

Rick

Moderator
Staff member
That's actually a very good question yodog. I've played with this but don't have a specific answer. For several years I used ice in my quench water and heat treated to 30 BHN, I believed it did make a difference in final hardness, after stopping the ice I'm now not so sure. My best SWAG currently is that possibly the ice will speed up the initial hardness (the time curve) but the final hardness over time is about the same.

A long time ago, 25-30 years, I believed that the harder the better. Having done a great deal of BHN testing keeping all loads identical and changing only the bullets BHN via heat treating I've learned that harder is not better and in fact can be and often is detrimental to accuracy and leading. Much better to use bullet BHN that suits the load, caliber and firearm. In top end loads in my long range match revolver that is 18 BHN, as hardness goes up from there accuracy degrades. In rifles such as my 30-30 and my 308 with velocities up to about 2,000 fps air cooled CWW at 12 BHN is the cats meow..
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D

Dusty Bannister

Well-Known Member
If the temperature of the quench water is a concern, then why not be concerned about the ambient air temp as well? A significant amount of heat is lost from the castings while one is dinking around removing the basket or tray from the oven, and turning and moving toward the water bath before finally plunging the basket into the water to the sound of that "sqush" of the quench.

Maybe the fact that I work in an unheated shed makes me want to avoid making a lot of heat in the hot summer, and being uncomfortable in the dead of winter when the shed is pretty cold. So the ambient temp is more like 50-90 which on a large scale is not all that much. Most of the writings suggest that one not delay in moving the castings from the heat to the quench, so perhaps that is more important than the quench temp. The quench starts the process, but does not finish it. Time and Metallurgy finishes the product. And for the most part it seems many feel the result is too hard anyway.

Sort of rehashing the question how much deader do you want to kill it?
 
Mike W1

Mike W1

Active Member
Without looking it up if memory serves me at all, Dennis Marshall said something to the effect of it wasn't the temperature of the water that did the job but the rapid change to the bullet. A few degrees difference apparently not making any big difference. Seems like it might have been in the RCBS Cast Bullet manual.
 
P

popper

Well-Known Member
LASC guy did a test years ago, it does make a difference. It is the RATE of cooling that makes the difference - quick 'freeze' vs slow. Lead has a specific heat conductivity BTU/Hr/Deg C. There is a maximum hardness that is the limit.
 
fiver

fiver

Well-Known Member
it is the speed of the cooling that makes the change.
even air cooled bullets are affected by rapid heat loss, found that out before I heated the shop.
 
D

Dusty Bannister

Well-Known Member
RCBS Cast Bullet Manual #1, page 31.
"After heating, open the oven door and quickly get the basket into the water. Speed is the all-important factor in quenching; there simply is no way that the quench can be too fast."

Everyone is free to do as they like.
 
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Ian

Ian

Notorious member
Rick wrote up a nice article, published on lasc, about how he minimizes the dinking around between oven and water part. I agree that time from oven to water is going to be more critical than water temperature, because how fast the bullets lose that first 50-75 degrees makes a lot of difference in final hardness as I have discovered the hard way.
 
pokute

pokute

Active Member
Sheesh, it isn't rocket science:
Phase_Diagrams_Image_004.png


All the action occurs right about 620F. In general, the smaller the grain structure the harder the alloy, so you want to get the temperature down below 600F or so as fast as possible. An additional interesting bit is that the outside cools faster, producing a "stronger" bullet by creating a compressed shell. A strong brine solution should work better than water. Of course, this is all theory, and I'll bet that it behaves differently IRL. I've never water dropped bullets.
 
P

popper

Well-Known Member
Actually it occurs below 450F (where most moulds run), when the alloy is BELOW the solidus line!! Yes, brine works better as the temp can be lower before freezing. I use a hot plate so it only takes a second or 2 to dump them.
 
pokute

pokute

Active Member
popper said:
Actually it occurs below 450F (where most moulds run), when the alloy is BELOW the solidus line!! Yes, brine works better as the temp can be lower before freezing. I use a hot plate so it only takes a second or 2 to dump them.
Click to expand...

The solidus line (clearly marked on the graph) passes through 450F for well over 10% tin - Your alloy is not a stable liquid at 450F, but a mixure of alpha Lead crystallites and liquid, as shown on the graph. It's not the freezing point depression that gives the most bang for the buck (though it certainly helps), but the boiling point elevation. Cooling efficiency is rapidly lost by steam insulation of the bullet.
 
Ian

Ian

Notorious member
pokute said:
The solidus line (clearly marked on the graph) passes through 450F for well over 10% tin - Your alloy is not a stable liquid at 450F, but a mixure of alpha Lead crystallites and liquid, as shown on the graph. It's not the freezing point depression that gives the most bang for the buck (though it certainly helps), but the boiling point elevation. Cooling efficiency is rapidly lost by steam insulation of the bullet.
Click to expand...

Precipitation-hardening temperature is considerably below the liquidus line. Like I wrote earlier, the most hardening effect is from the initial cooling from treat temperature. Glycol antifreeze and water, 50/50, boils at about 270°F and is a much more suitable quench media than plain water.
 
pokute

pokute

Active Member
Ian said:
Precipitation-hardening temperature is considerably below the liquidus line. Like I wrote earlier, the most hardening effect is from the initial cooling from treat temperature. Glycol antifreeze and water, 50/50, boils at about 270°F and is a much more suitable quench media than plain water.
Click to expand...

Precipitation-hardening temperature is the band on the graph between the liquidus and solidus lines. Is the graph not showing up for everybody? Nobody seems to be referring to the phase diagram graph that I posted. Organic lead compounds from reaction with glycols are probably a lot worse than Lead Chloride.

Again, I'm more than willing to accept that things don't behave in the lead pot exactly according to the phase diagram, but the phase diagram is the only guide we have.
 
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popper

Well-Known Member
I don't use tin (it doesn't add much hardness) and you don't have a any curves for the alloy I use. As Ian stated, it's the undercooled/supercooled structure that adds the hardness. Water solutions do work better but I've gotten hardness up to >36 BHN in plain ice water. Most of mine are coated anyway so the 'steam' has little effect. No, the precipitation occurs AT/BELOW the solidus line. Else heat treating would NOT work!!
 
Rick

Rick

Moderator
Staff member
Most likely max hardening of a Pb/Sb alloy would be between the liquidus and solidus lines But ask yourself this, does water dropping from the mold work to strengthen bullets? Of course it does, not to the same degree or consistency that convection oven heat treating does but it does strengthen (harden) them. When dropping from the mold they are well below the liquidus/solidus temp or you wouldn't be dropping bullets, you would be pouring alloy.
 
Ian

Ian

Notorious member
I wasn't referencing the graph because it only represents the binary Pb/Sn, which doesn't quench-harden anyway.

The context of heat treated bullets is ternary alloy containing Sb and possibly As/Cu/S, which has very complex properties of precipitation-hardening due to the interaction of the various trace grain refiners often present in alloy such as WW. For a purely theoretical discussion, ternary Pb/Sb/Sn alloy has a simple phase diagram where the precipitation temperature is still below the liquidus line. The whole mess of the alloy doesn't have to be bumped above the net liquidus temperature to achieve the PH effect, it just has to be warm enough for the molecules to loosen up a bit and re-situate themselves as they cool and age.
 
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