[Nero Steptoe]

MODERN APPLICATION NEWS
MARCH 1998

The Metalworking Idea Magazine

Cryogenic Tempering Boosts Parts Life Up to 400%
By Larry Olson, MAN editor



Rings and pinion gears, valve springs made of H-11 or H-13 steel, and brake rotors for heavy haulers and race cars, have lasted two to four times longer after cryo treatment.
Cryo processing has three benefits, specifically increased dimensional stability, stress relief, especially for aluminum, titanium, composite materials, and improved wear or abrasive resistance.


The process completes the austenite to martensite transformation that occurs during heat treat in steel alloys. Heat treating increases hardness in tooling, while post-heat treat cryo processing with a mild draw increases hardness by an additional 1% - 2%.

The process uses Liquid nitrogen to cool parts from room temperature to –300F at a rate of ½ to 1F per minute for maximum stress relief. Then, maintaining the parts at –300F for 18 to 36 hours completes the austenite transformation. The more carbon in the material, the colder and longer the parts are kept at low temperature, according to the customer’s specific needs. After the “cold soak,” the parts are returned to room temperature at ½ to 1-minute rate. Usually, three heating and cooling stages (called a “triple draw”) are included, depending on the material, with a one-hour hold at the temperature extremes.

Cutting tools are the largest market for the process, including drill bits, endmills, slitter knives, punches and dies. Cryo processing also is used to treat TiN coated tooling, HSS (high-speed steel) saw blades – bandsaws, circular saws, jig saws, M-series blades – and carbide-tipped saws (C-2, C-3 and C-4). In the 1995 ASM heat treater's guide, 67 out of 77 tool steels listed have cryogenic stabilizing specified as the only method to increase dimensional stability after heat treat.

Cryo processing also is used to stabilize aluminum and titanium, since they are often hard to handle during machining. In aerospace applications, cryogenic tempering conditions the metal in aluminum optical benches, so that large temperature variations can be tolerated with minimal distortion. Once a part has been cryo treated, additional cryogenic processing will not usually make any difference. When a tooling manufacturer has included cryogenic treatment as part of the process, additional treatment by the end user will usually have no effect.

Multifaceted tools or materials need to be separated into it individual components for cryo processing, since the rates of cooling may vary slightly between different grades of metal. Smaller items and more intricate tooling process better if disassembled. It is less critical on the larger items; for example, processing is not a problem for a cast iron or aluminum engine block with steel sleeves without disassembly.

Consistent Results for a Wide Range of Applications:


Calsonic Yorozu Corporation, a Tennessee subsidiary of Isuzu, uses a large HSS twist drill to manufacture chassis. The drill is about 1’ long by 7/8” diameter and costs about $80. Two drills are mounted on a robotic arm in an assembly line and usually last for only 100 holes. Cryo treating the drills costs about $10 and increases the tool’s life between 20% and 50%. Production is now getting between 120 and 150 holes from a single drill with less downtime.
Hexell is said to be the world’s largest manufacturer of composite materials. The company has been cryo treating the tooling used to cut Kevlar, titanium and aluminum during production. They are a large tool buyer, and the 300% increase in tool life from cryogenic tempering saved them about $1/2 million in tooling cost during 1197. The treated tooling includes ¼” and ½” endmills, about half of which are coated, and a scissors shear.


The teeth of the backhoes (called “frosties”) used to dig frozen perma-frost in Alaska were wearing out too quickly. After cryo treating, the life of the teeth increased from about four hours to 16 hours. In another heavy-duty application, a paving equipment manufacturer builds and supports paving equipment to mix asphalt. The company uses 12 flute endmills, called “slugger bits,” to cut stainless steel. The bits, some of which are coated, cost $20 to $50 each. After cryo processing the tooling life increased by two to three times.

Gears in heavy equipment or transmissions, cast iron or forged items also can benefit from processing. When the military tested cryo treating helicopter gears in the 70’s, they found that the process improved durability and reduced noise, which turned out to solve several problems in combat. Noisy working environments are improved through cryo treatment by providing greater longevity and safety for gears and moving parts.

The process has also become popular on the race car circuit among such well known names a Cale Yarborough and Tony Furr in the John Andretti car, and NHRA professionals, such a Kurt Johnson, Larry Morgan, Allen Johnson and Roy Johnson of ProStock. Race car owners and drivers are always looking for any performance advantage. In cryogenic treatment of their cars’ parts and engines, if one of the materials in a metal-to-metal contact surface is carbon-bearing, it is a good candidate for cryo treating. This is especially true if it has already been heat-treated.

In an experiment in another sport, golf balls were dropped from 8’, before and after cryo treatment. The balls rebounded 2” higher (about 2%) after treatment. In another test, cryo treated golf clubs showed a 3% to 5% improvement over untreated clubs. Also, One Cryo is offering its own special line of softball bats, tempered with cryo treatment.

Equipment, Service and Processing Support:

Although the operation is only three years old, the process dates back over 50 to 60 years with many practical innovations and improvements since the 60s. One Cryo consists of three separate service centers located in Orlando, FL, Seattle, WA and Wasilla, AK. Regional market variations have meant that the parts usually handled for processing in Alaska are different from the parts processes in Florida.

Every area of the country has much to offer especially the Midwest corridor from Cincinnati to Detroit, the heavy industry areas of the eastern US and the racing areas along the eastern seaboard. Companies in Oregon, UK and Australia have also shown an interest in setting up franchisee operations. The western US is also an active area in supporting aerospace manufacturing Boeing subcontractors are involved in discussing the cryo treatment of their in-house tooling for increasing tool life.

This relatively undiscovered industry has also developed its service side to provide cryogenic processing in response to specific regional niches. One Cryo is equipped to provide an in-house design and manufacturing capability, with engineers on staff for design and fabrication of individual processing systems specific to their customer’s production needs.

[cracked butt]

But does it make my steaks taste better?:D

[Art Eatman]

The idea for gun-barrels is that they be uniform in behavior during the temperature change from ambient to heated condition. Improved consistency in the "tuning fork" behavior.

Art

[Wildalaska]

See I knew it worked!

[Destructo6]

cryogenic tempering saved them about $1/2 million in tooling cost during 1197.
That's a lot of money back then.

I still don't buy it. Anecdotes mean very little. I want evidence, like there is for heat treating (ie Rockwell scales), that there is a measurable change.

What does this paragraph mean?
Cryo processing also is used to stabilize aluminum and titanium, since they are often hard to handle during machining. In aerospace applications, cryogenic tempering conditions the metal in aluminum optical benches, so that large temperature variations can be tolerated with minimal distortion. Once a part has been cryo treated, additional cryogenic processing will not usually make any difference. When a tooling manufacturer has included cryogenic treatment as part of the process, additional treatment by the end user will usually have no effect.
What do they mean by, "hard to handle" and how does cryo-ing make them easier to handle (too hard to handle, too cold to hold?)? I've machined quite a bit of aluminium and a bit of titanium and have not found them hard to handle.

[Joe Demko]

cryogenic tempering saved them about $1/2 million in tooling cost during 1197.

That's a lot of money back then.

LMAO!!!

Note: We need a coffee spewing smiley.

[Nero Steptoe]

Just thought I'd pass the article along. Didn't edit for content. Oh, well, at least the guy didn't claim that metal isn't made up of molecules! :)

[mete]

Nero has shown in the past that he is incapable of dealing with logic and science so his comments should be ignored. The steel in the quoted article is TOOL STEEL not typical barrel steel . ( apples and oranges are different ) As for stress relief by cooling it says " three HEATING and cooling stages " , I wonder why they have to heat it ? And metals never will have molecules even if nero prays for it every day.

[Art Eatman]

"...metals will never have molecules..."? Huh? Of what, pray tell, are they composed? I know of nothing, organic or inorganic, which is not made up of molecules...Air, water, steel, people, flowers. I really do suggest reviewing Freshman Chemistry! :D

Destructo6, I know that some aluminum alloys can tend to "gouge" if the cutting tool is not of the proper shape. In the earliest days of working with titanium, machining was said to be difficult, although I'm now vague on details after 40 or so years. It and tungsten were often formed by casting to minimize the amount of machining required to finalize a shape. A lot has been learned--by some--in 40 years, of course.

Art

[Handy]

Art, I don't think you'll find many Helium or Gold molecules. A molecule is a unit made of more than one atom. Free oxygen atoms bind with themselves creating O2 molecules. Iron oxide is a molecule. I don't know whether iron binds to itself to produce Fe2, but if it doesn't it's not a molecule.

Alloys are mixtures of various metals. When you add pieces of oxided metal for strength, that is no longer an alloy, that's a metal matrix. A crystal is an arangement of nested atoms or molecules. It is not a molecular structure. Steel is both an alloy and a crystal. It may contain some molecular ingrediants but is composed largely of metal atoms, arranged in a crystal as it cooled. I think Mete is therefore correct.


I think we're fooling ourselves with the cryo stuff. Even the nicest gun is crude (metalurgically and dimensionally) compared to the parts of a jet engine. Cryo treatment for most guns is probably only a little more useful than cryo treating a bench vise or anvil.

[Ledbetter]

Not molecules; "metal atoms."

:scrutiny:

Coupla things:

Stainless steel has other metals in it besides iron (nickel for one).

Molecules in a matrix are not "atoms."

[mete]

Art and Handy, I suggest you go back and study chemistry. Here are the FACTS. There are three basic types of bonding; ionic, covalent, and metallic. These are significant differences. Metals have metallic bonds ,thats what gives metals their properties. Groups of metal atoms form crystals (NOT molecules). Groups of crystals form grains. I didn't make it up ,mother nature did. unfortunately there are many who refuse to learn. I guess I'm the only metallurgist in this forum but I will continue to try to educate people Metallurgy marches on !

[Handy]

Mete,

I already agreed with you and said that metal crystals are formed of metal atoms, not molecules. What's the problem?

Ledbetter,

Who said "molecules in a matrix are atoms"?


Is anybody reading each other's posts?

[Ledbetter]

"Steel is both an alloy and a crystal. It may contain some molecular ingrediants but is composed largely of metal atoms, arranged in a crystal as it cooled."



I am no metalurgist, if metal is made of "metal atoms" with "molecular ingredients," so be it.

I guess I am confused by the fact that salt crystals are made of molecules of sodium chloride, unless I'm mistaken again.

[106rr]

Can I take that with a grain of salt?

[Handy]

Simple atomic ingredients of steel that are metals include stuff like:

Iron, chromium, molybedenem, tungston, etc.

Carbon is the other main ingrediant in steel. Carbon is normally found bound to something, so it may or may not exist in the alloy as an atom or as a carbon compound (also known as a "molecule").

A crystal (any crystal) can be composed of a matrix of atoms, molecules, or both. Salt and ice are crystals composed of compounds. Solid gold is a crystal composed of one kind of atom. Glass is a solidified form of atomic silica that hasn't crystalized.

Clear as mud?

The main ingrediant in a rifle barrel; iron, is composed of individual iron atoms (Fe) arranged in a crystal.

[Frohickey]

Semantics.

I think the confusion stems from Freshman Chemistry classes, where students are first introduced to atoms, molecules, etc. Experiments are usually done in solutions, and so, the notation used is as if it were molecules of 'stuff'.

Common table salt, not in a solution, is a crystal. A crystal of Sodium (Na) and Chlorine (Cl). Here, its really not a molecule anymore, where a particular sodium atom is distinctly paired with a particular chlorine atom. This is what mete is talking about. Unfortunately, most people stop taking chemistry classes long before the course material gets into crystals.

Back to cryo-ing, I still think that the mere cooling of an object wouldn't reduce the stress within a material. I think its the type of 'cooling', sudden or very gradual that is what reduce stresses.

If we can 'grow' a rifle barrel, the same way a crystal of silicon is grown, would that make for a stress-free material ideal for a rifle barrel?

[owen]

mete, isn't there a line on a TTT diagram for say 4140 that is well below room temperature? Metallurgy was a long time ago for me. It was my understanding that the intention of the process was to force a complete transformation of the microstructure, which was otherwise incomplete at room temperature.

[mete]

Handy---there are no "molecular ingrediants" in metals. ..Frohickey--- stress relief requires movement of atoms- the higher the temperature the more the movement, so you wouldn't cool it to stress relieve. Grow a single crystal barrel ? now that is intriguing. BTW glass is described as a supercooled liquid.... Owen--- You would expect complete transformation of austenite to martensite at room temperature in 4140. With more complex alloys like some tool steels you would only get partial transformation. We then freeze them to complete the transformation.

[Art Eatman]

I stand corrected on atoms vs. molecules, as regards iron or other metals...Fe be an atom; FeO be a molecule. :) And Fe + H(2)SO(4) = a messy battery box.

There has been quite a bit of writing about "growing" metalline crystals in space. IIRC, the tensile strengths are amazingly high.

I disremember the tolerances for turbines; anything spinning at 120,000 rpm has gotta be closer than "purt' near". Are they closer than the one or two ten-thousandths of an inch for some air-gauged barrels?

Art

[Handy]

Mete,

I had no way of finding out what form the carbon was in when it was alloyed into the steel. If you say it's free carbon and not a carbon compound, fine.

Art,

I was speaking more metalurgically. Metals that see constant temperature variations in the thousands of degrees are likely more alloyed, forged and machined than a length of steel pipe with a precise hole swaged through it. If Lockheed designed a Mini14 barrel it would be factory dimensions but never loose accuracy as it heated. It would also cost $23,000. But you can't make aerospace parts with billet, a Shopsmithy and hand fitting.

Even the most precise gun is still carved out if a block of basic, homogenous metal. Applying spacey metal treatments is like Hollandaise on hotdogs.

[Badger Arms]

I think that, perhaps, 50 angels can dance on the head of a pin. But that all depends on if the planets are in line. Further (or is that Farther... :scrutiny: hell, WHATEVER) it all depends on what you definition of the word is is, so to speak. I mean, if is means is and always has been then, Well...:rolleyes:

MY GOD, WHO CARES. I don't think that the basic laws of the universe are being violated anywhere here. Give me a peer-reviewed scholarly journal article to read. Then maybe some of you can crawl into a corner or eat crow and the others can gloat, hoot, hollar, whatever. Endless debate on multiple threads doesn't seem to help.

Now I'll add, if it doesn't HURT and oftentimes HELPS, who cares what the definition of the word "Molecule" is. I still haven't figured out how a network works, but I use it because it works (or at least my system administrator says it does).

[Handy]

Oh yeah, you probably want to get back to the IMPORTANT stuff that gets discussed on computer message boards.;)

[Art Eatman]

Now, now, Badge; remember a thought from an old song:

"Tranquil, tranquil;
Full of peace and Equanil."

Valium works equally well. :D

The question isn't really how many angels are dancing on the head of that pin, but how many atoms are there? Is the pin alloyed? Carbon steel or stainless? Austenitic or martensitic? Hey, mount it in the little plastic block and polish it with 2000 "grit" on the felt wheel and check it out at 400X. (Come to think of it, there are more than just the one question!)

How can one not care? How, I ask! Why, the very fate of nations might hinge upon the answer, not to mention our understanding about the various steels and treatment processes available whereby we have better rifles!

(Bet you didn't think I could get this back on track, did you?)

:D, Art

[mete]

Art, NOW YOU'VE GOT IT !!!

[Detachment Charlie]

I just had to mention copyright....thanks for the attribution.

The subject of cryo treating various metals at various stages of production and the benefits derived is -- has been --- and will probably be -- kicked around machine shops for years.
In all the processes of metalworking, heat treating is one of the last that retains a "little bit of art and a little bit of magic." It is a demanding science and process. Cryo is, relatively, the new kid on the block. It will be used, explored, developed and perfected. Is it the answer to all problems? No. A professional discussion of cryo can get as fractious as .45 vs. 9mm.
Cryo is a fascinating subject. It is a subject Modern Applications News will continue to cover. How do I know?
Because I am the new editor of the magazine.:rolleyes:

[Nero Steptoe]

I don't know why it didn't occur to me that my copying and posting the article re cryo might have been a violation of copyright. Certainly didn't mean to step on anybody's toes.

I've been aware, from the beginning of this discussion, of my own ignorance regarding metallurgy. I found the article and thought some might find it interesting. My ignorance of metal structure is irrelevant to the question at hand: "Does cryo treatment affect the structure (whatever that structure is) of barrel steel in a positive manner?? Does cryo relieve stresses in metals??"

Apparently, there are many metallurgists who believe that cryo works, and, from the article, there seem to be many end-users of cryo'd products who have found that cryo works.

According to our resident expert, cryo didn't work, period. Not in tool steel....not in any steel.

Having said everything that I've said so far, I'd like to add that I wouldn't spend $.05 of my money having a barrel cryo'd. (Not that I don't think the cryo would work, but that any marginal accuracy increases would be irrelevant to me.)

Either cryo works, and the many companies now offering cryo treatment are offering a beneficial service, or all those companies are frauds and scams. Time will tell.

[Handy]

I have no doubt that cryo works. It's more a question of application. There may be reasonable uses on some sort of firearm, but I doubt that the process has any use on a $600 hunting rifle.

[Detachment Charlie]

Cryo, as a process, is neither a fraud nor a scam. Also, it is not the universal answer. In some applications it works very well. In other applications it's benefits are small. Yet, in others the benefits are still being discussed.
A quick point, the stage at which the process is used is critical. As an example, I've read where a premium barrel manufacturer uses the process with fluted barrels. However, the cryo treatment is employed after the fluting of a barrel.
Also, the material being treated is most important as is the process itself, like other heat treatments.
Heat treating is one of the most complex technologies in all of metalworking.
P.S. Metalworking and firearms have a fascinating shared history and future.
Thanks for reading.:D

[larryw]

I'm not smart enough to know if cryo is art, science or pixie dust. I am smart enough to appreciate the results: I own a light barreled rifle that would spray bullets all over the place as the barrel heated up. It suddenly became a tack driver with no other change but a $40 cryo treatment.

[Art Eatman]

Thanx, Larry. Just shows to go ya, one test beats a thousand expert opinions...

:D, Art

[Badger Arms]

Art, I'm going to have to take more little purple pills now?

[Art Eatman]

Aw, just stay with the regular dosage, Badge. :)

I'm still rolling this atom/molecule thing around. Part of the problem for me is that Inorganic/Quan/Qual was back around 19mumble-mumble. Before JFK, if that's a hint. :) And then my engineering world turned to dirt, as in dams and reservoirs...

"Air molecules" are spoken of, but air is a mix--yea, verily, like unto an alloy. I realize ya got two atoms each of Oxygen and Nitrogen, making O/2 and N/2, yada, yada. But how about the inert, trace gases?

Are two Oxygen atoms chemically bonded as a molecule of O/2? But a gaggle of Fe atoms merely hang out together?

Art

[Handy]

"Are two Oxygen atoms chemically bonded as a molecule of O/2? But a gaggle of Fe atoms merely hang out together?"

Correct.

[Art Eatman]

Hokay. A summary of all this seems to be that, first, we know that stress-relief of machined or welded steel fabrications is beneficial.

In the past, some sort of heating to temperatures well above ambient and then cooling at some controlled rate has been the normal procedure.

Cryo-cooling as stress-relief is still mostly unknown, still in the cut-and-try stage, at least in the gunsmithing world. There are still arguments about repetitions, about rates of cooling and of re-warming to ambient, and even whether a further heating/cooling might be desireable.

Close enough?

Reports from shooters vary as to the success for their particular rifles. Some found it beneficial; others have reported no notable change (harking back to some TFL posts).

Art

[daniel (australia)]

Here's my take:

If you take a piece of typical medium carbon steel and heat it good and hot, the internal crystal structure rearranges itself into a structure called austenite.

If you then cool this steel slowly it transforms again as it cools to a stucture composed of grains of more or less pure iron (ferrite) and grains composed of layers (lamellae) of ferrite and of iron carbide. The lamellar structure is known as pearlite. This mixed structure is comparatively soft.

If, on the other hand, you cool the hot steel very quickly, the austenite structure undergoes a rapid transformation to martensite, which is composed of very fine needles of carbide in a ferrite matrix. This is glass-hard and very brittle. You can then temper this structure by more or less warming it, to allow some of the carbide to begin to rearrange itself into a less hard but tougher arrangement (under a microscope the needles appear to get less sharp). By the way, the austenite-martensite tranformation is accompanied by a small change in volume, as the atoms and molecules (eg Fe3C) rearrange themselves.

Now, here's where cryogenic quenching comes in: in some alloys and under some circumstances no matter what you do there's some untransformed austenite left at room temperature. This can be a problem in some situations as retained islands of austenite in a martensite matrix cause internal stresses (due to the volume difference) and soft spots. This has been a particular issue in certain tool and die alloys, where the austenite-martensite transition is not complete at room temperature. Cryo has been a real success here, in driving the martensite transfomation to completion, and this is indeed the mode by which it works to relieve internal stresses and improve physical properties _in those specific alloys_.

Typical rifle barrels don't have this problem: the martensite transformation is complete at room temperature in the alloys typically used (eg 4140, 416). IMHO Cryo treatment is just superfluous for rifle barrels.

[Art Eatman]

Hokay, Daniel, lemme run this by you (and anybody else). It's a lot of inductive reasoning, I guess; I'm not in love with the idea:

If the piece of steel that will become a rifle barrel is not homogeneous in its mixture, there will be stresses created by the machining process as one cuts across areas of non-homogeneity. After machining, stress relief via heating and quenching, etc., makes everything all wonderful--or is supposed to.

We know that a barrel acts as a spring; we know it is subject to rapid heating and cooling. Stress relief apparently/allegedly allows more uniform vibrations during different conditions of temperature. (That is, it should vibrate the same for the first shot of a string as for the fifth shot.)

Now, whether some barrel steels inherently need further cooling below ambient to complete a martensite transformation, I dunno. However, since there are some reports of improvement via cryo-cooling, it seems to me that its benefits cannot be rejected out of hand.

I guess if one knows his barrel is of 4140 or of 416, worrying about cryo-treatment is unnecessary nit-picking.

Art

[mete]

My last comment here guys. "stress relief via heating and quenching" no, heating and cooling slowly. Let me describe things this way Suppose you make a barrel that is not straight. You bend it to straighten it , this puts residual stress in the barrel. As you shoot it this temporarely relaxes the stress and the barrel goes back to to the original nonstraight condition .as it cools it will return to the straightened condition. This doesn't do much for accuracy. If you heat the barrel to stress relieve it then as it heats or cools during firing there will be no movement. Remove stresses and you get a more accurate barrel .Simple as that !!!

[Art Eatman]

Hokay, so pardon the nitpicks*. I'd like to make sure I got the jargon straight, in talking about stuff where I "sorta know" some of the generalities:

Quenching = rapid cooling, having to do with tempering?

Stress-relief temperature changes are slow, whether in the heating or the cooling?

Art

* For instance, I don't fuss at people who speak of a reservoir's "silting up". Reservoirs trap sediments, some of which might be silt. :)

[Peter M. Eick]

Art,

Let me correct you slightly.

Reservoirs are where you get oil and gas from. Silt is useful as a seal to keep the oil and gas in place so we can come along and drill into the reservoir and produce that oil and gas.

By the way, Hi from East Texas to West Texas (where all the good reservoirs are!).

[BHP9]

So what does all this techno info have to do with accuracy in rifle barrels, tests show not much.

In tests conducted by the NRA recently the only advantage seemed to be with standard weight rifle barrels of production line quality not match barrles or heavy match barrels and the improvement in accuracy in my opinion was so small that other variables probably had as much to do with the increase in accuracy as the cryo treatment.

In short you are wasting your money by having your match barrel cyro treated.

At our own shooting range heavy barrel match rifles that were not cryo treated often outhshot those that were with groups often going into 1/4 inch at 100 yards out of semi-auto AR15's that were not treated.

[JohnBT]

Most informative. Thanks.

Of course, with my luck I would have a barrel treated and then find out the chamber was cut crooked.

John

[daniel (australia)]

G'day Art

"If the piece of steel that will become a rifle barrel is not homogeneous in its mixture, there will be stresses created by the machining process as one cuts across areas of non-homogeneity. After machining, stress relief via heating and quenching, etc., makes everything all wonderful--or is supposed to"

Well, um, yes and no. There may be residual stresses due to machining, especially if done badly (e.g. blunt tooling -> high friction - > localised heating). Residual stresses may also be due to plastic deformation, such as occurs in button rifling or straightening or, to a more significant degree, hammer forging. Such residual stresses may or may not be significant, and may or may not be a problem, depending on the end-use of the item. In the case of rifle barrels however, _unevenly-distributed_ residual stresses may cause the barrel to "walk" as it heats up. In the general run of barrel steel therefore these stresses may be relieved by normalising, being controlled heating and slow cooling.

"We know that a barrel acts as a spring; we know it is subject to rapid heating and cooling. Stress relief apparently/allegedly allows more uniform vibrations during different conditions of temperature. (That is, it should vibrate the same for the first shot of a string as for the fifth shot.)"

Yep.

"Now, whether some barrel steels inherently need further cooling below ambient to complete a martensite transformation, I dunno. However, since there are some reports of improvement via cryo-cooling, it seems to me that its benefits cannot be rejected out of hand."

In certain very specific situations, there is a different mechanism which can lead to residual stresses. This is that due to the difference in volume of austenite retained in a martensitic matrix, and is usually a product of specific alloy compositions, often exacerbated by long soaking at austenitising temperature. Stresses due to _this mechanism_ may be relieved by ensuring all the austenite is transformed to martensite, and in some cases, especially with certain tool steels, cryogenic quenching is necessary to do this.

Retained austenite is not at all likely in the steels used in rifle barrels, which complete the transformation to martensite at well above room temperature.

What I'm getting at is that cryo is not a generalised stress-relieving process. It is specific to a particular cause of residual stresses in certain specific situations, where the results make it very worthwhile. These situations don't include the treatment of steels typically used in rifle barrels.

BTW most rifle barrels these days are either of medium-carbon CrMo steel, usually 4140, or a machinable martensitic stainless, usually 416R.

[daniel (australia)]

Art

"Quenching = rapid cooling, having to do with tempering?"

Yes, and sort of. In the context of heat treating typical martensitic steels quenching means cooling sufficiently rapidly to cause the transformation to martensite: cool to slowly and it won't happen. The rate of cooling required depends on the alloy and the cross-section of the workpiece. Some alloys for example, require very severe quenching, into brine for example, to produce martensite to acceptable thicknesses. These are said to be of low hardenability. Othe alloys will be sufficiently quenched in oil or even air (oil-hardening and air-hardening respectively).

Now once you have quenched to martensite you have an extremely hard but brittle product, which is not terribly useful. Tempering addresses this by controlled heating of the workpiece to cause some diffusion of the structure, thus progressively increasing toughness and lowering hardness with time and temperature.

"Stress-relief temperature changes are slow, whether in the heating or the cooling?"

For these types of steels, broadly speaking, yes.

[daniel (australia)]

G'day BHP9

"In tests conducted by the NRA recently the only advantage seemed to be with standard weight rifle barrels of production line quality not match barrles or heavy match barrels and the improvement in accuracy in my opinion was so small that other variables probably had as much to do with the increase in accuracy as the cryo treatment."

I'm not surprised. I've yet to see any persuasive evidence for cryo treatment of rifle barrels.

[daniel (australia)]

Ooops, edited to remove duplicate post produced by impatience:rolleyes:

[Badger Arms]

Daniel,

SHHHHHH, sheez, don't you know the gun Nazis will hear you speaking about, well, GUNS. I didn't know you guys could own guns down there anymore.

Seriously, is there anybody down under who is doing this cryo stuff?

[daniel (australia)]

G'day Badger

Yeah, we can still own guns, at least for the time being :(

As for cryo treatment, there are outfits offering it for tools and dies, and certain other applications. One is run by a bloke I used to work with many years ago.

I'm not aware of any advertising it for improving rifle barrels, but there again we have fairly strict laws on misleading advertising;)

[Ledbetter]

Welcome, and best wishes to you across the water. Thanks for the good info.

[Art Eatman]

Peter, no argument about them there subterranean reservoirs of awl and natgas.

Howsomever, ya got the Lake Conroe reservoir and the Lake Houston reservoir...and Sam Rayburn and Toledo Bend and other examples of that good French word, so beloved of the USCE, the TWDB and various river authorities. Ya cain't ignore the Beaver Clan!!! It's one of the biggest dam clans there is!

(I once worked with a dam engineer who, when he was irate, would exclaim, "Grand Coulee!" 'cause that was the biggest dam(n) he knew of.

:D, Art

[Peter M. Eick]

Gosh "Hoover" it!


(It just doesn't sound right)

Yes we have the water, but after 49.67" of rain at my house last year I will gladly trade you some oil for the water. To bad we cannot arrange that one.

Keep in touch and hope all is well out your way.

[stubby]

I didn't understand half of what I just read but I am impressed with the knowledge of the posters. Makes me feel like a dork though!:banghead:

[redneck]

I don't know a lot of the particulars involved in making a rifle barrel, but I make knives and do my own heat treating, and have read a fair bit on it.
Maybe it will help some people if I lay out the very simple process that goes into heat treating one of my knives.

I start off with annealed precision ground steel. It is garuanteed within a certain tolerance for uniform thickness, but due to handling and stuff its never quite straight. Basically it has been bent, and due to it bein soft, it has taken a set bend (some stress build up, more importantly this is the shape it wants to stay in, like a warped peice of wood)
I do all the cutting grinding and machining, and by the time the blade is ready for HT, it looks completely straight. The grain/crystal structure still remembers the previous bend though, I just cut and ground stuff off till it was flat. So before the actual hardening process, I normalize the steel. This is simply heating it to critical temp (it becomes non magnetic, for the O1 I use this is around 1440 deg) and then cooling it off very slowly. By doing this you excite the atoms (or even molecules if you feel better calling it that ;) ) They start moving an slidin around past each other, if you heat it too much they can move so freely that it becomes liquid. So now you've got the little guys movin around some, and you cool the stuff down slowly, they gradually relax into a more fixed state. And they settle there with the peice in its present form. No more stress, the crystal structure is aligned with the present shape.

Now its time to actually harden the steel. Pretty simple, heat it to critical temp and quench in oil. This was explained pretty well earlier in the thread. Austenite into Martensite, carbide matrix etc. All that complicated stuff. Now the steel is much too hard to to be used for anything, its very brittle.
So its time to temper (heat at 400 deg F for 2 hours, let cool slowly, repeat). This releives stress and it brings the steel into a useable range of hardness. Basically you have the same thing going on as the the normalizing process from earlier only on a smaller scale though.

Now for the cryo. I don't do this to my knives, but had it done on a few that were professionally heat treated (I can't do stainless, takes too much heat and too complicated) The cryo treatment is supposed to complete the transition from austenite(not good) to martensite (good) Some very accomplished bladesmiths I have talked to, seem to be of the opinion that if the heat treat is done properly to begin with, there is no need for the cryo. That makes sense. Basically the cryo is insurance.

I hadn't ever heard much of cryo being used as stress relief, but that makes sense. The same basic concept I talked about for normalizing takes place. Your dealing with a sort of phase change. Only you don't actually go far enough to get the change. Think of water, when its warm its in a liquid (disordered) state. When its cold its a solid (more ordered) state. So your using the extremely low temp of the liquid nitrogen to bring the steel into the most ordered state possible.

Is it needed for a gun barrel? I'd say yes and no. Its like insurance. If everything was done properly, the barrel should be fine without it. If there was a problem somewhere, it could possibly solve them.

Anyone else vote this for the most boring thread in the short history of THR? All I really care about is does it work? Beyond that I would like to chalk everything up as "01magic":neener:

[Art Eatman]

redneck, what's boring to one guy might not be so to another. And, if something's boring, it's easy enough to not read it. :)

Thing is, questions come up from time to time about all manner of stuff. It's helpful to know *why* something happens or does not happen--rather than to merely know that "ya turn the key and the car starts."

Art

[mete]

Redneck , retained austenite is not a problem with O1. As far as stress relief - when you are stressed out do you jump into a tub of ice water or into a HOT tub ?

[redneck]

Mainly joking about this being boring. These discussions come up all the time on bladeforums and can go way beyond what anyone on the forum really understands, except for the 2 chemists and 1 metalurgist in the group ;)

Mete
I know that retained austenite is not a problem with O1, that is why I don't cryo treat my O1 blades. I had it done on a few ATS34 blades that I had professionally done. Mainly because it only cost $4, and I wanted to see if it worked. (the knives cut very well, and hold it very well, better than production knives in the same steel. Was it cryo or just the small batch HT? Couldn't tell ya.

As far as me jumping into a cold tub, thats not a very good analogy.
The idea of tempering and normalizing is that you get the atoms moving, and relax them into a matrix that is stable and stress free. An example is using leaf springs off a truck to make knives. A big leaf spring can be cut into a small enough section that it seem straight. The bend is still there in the grain structure though. If you don't normalize the steel, alllowing the grain to realign itself, it will most definitely end up in a warped knife.

Now the cryo treating simply continues the process of stress relief. Some stress builds up after heat treat because you have a very rapid change in crystal structure. It would be best if you could normalize again, but that leaves you back at square one with a soft peice of steel. You can heat to a limited temperature though, and still come out with the desired hardness. This gets the atoms moving a little and relieves stress as they relax back into a more fixed position as the steel cools. The idea behind cryo is that if you can't work on the grain structure to the same magnitude by heating it because you get it to soft, so you prolong the cooling process by taking it way below room temperature. The atoms relax into a more and more ordered state as the temperature drops. So you keep dropping the temperature as long as possible. When you bring the steel back up to room temperature, they're in a slightly less ordered state, but the stress has been releived.
Like I said before, on a gun barrel I don't think its anything more than insurance. Its likely that if there was a problem with some part of the process, it could make a difference. But if everything is done properly from start to finish its probably doesn't matter.

[mete]

I assume that you have not read all my posts in this forum ( here and in the gunsmithing section under barrel fluting) where I have explained at some length why cryo does NOT relieve stress . It seems that I am the only metallurgist in this forum but many would rather believe advertising hype.

[Badger Arms]

Mete, if you are an expert, there is always another expert that will DISAGREE with you. I'm not an expert and I disagree. While that doesn't hold much weight, the intellectual discussion revolving around it is at least enlightening to many of us non-experts out there.

Is it POSSIBLE that cryogenic treatment will relieve stress?

[redneck]

Actuallly in this thread you haven't done much more than tell everyone that your a metallurgist. On the first page, you did explain why steel doesn't have molecules, but thats basically a matter of terminology and for the idea in question it doesn't really matter if you call them molecules atoms or crystals. Everyone knows that we're talking about the basic building blocks of the material.
On the second page you explained why a barrel should be normalized. I pretty much explained that also, and agree with you.
You have not explaned anything about the actual cryo process besides telling us over and over that we are wrong. So, since you are a metallurgist, why don't you explain why cryo treatment doesn't relieve stress, or just exactly what it does.

I know that the austenite to martensite conversion is a non issue with the steels typically used in a gun barrel. And at the hardness level a barrel is usually at, you should be able to get adequate stress relief through normalizing and tempering, since you can use a much higher temperature for the tempering.

However you seem to be disagreeing that by lowering the temperature/energy of a material you bring the atoms into a more ordered state. Even though you say that by getting the atoms moving (via heating) and then slowly cooling will relieve stress. You seem to be contradicting yourself here.

I don't know what advertising hype your talking about either. I got all my info from articles on heat treating and from a few chemistry classes for engineers. No I'm not an expert. But since you claim to be, why don't you explain it?

[mete]

Redneck , I have been trying to explain the basics because without understanding that you can't go farther. That metals don't have molecules is a MAJOR point. My words are not casual. Tempering is done between 300 and 1100F, stress relief is typically 900 to 1250 , normalizing is above that ( above the transition temperature).Cooling slowly ( to room temperature ,maybe I didn't make this point clear ) ,after stress relief avoids adding stresses from the cooling itself , very important when dealing with complex shapes. Again the basics , to relieve stress atoms MUST MOVE. The ability of atoms to move is proportional to temperature , therefore you heat to stress relieve.When typical stress relief treatment call for 900F thats because it takes that temperature to get significant atomic movement to relieve stress. By the way as far as retained austenite , typical barrel steel of 4140, transformation to martensite is complete at 425F.

[Detachment Charlie]

See, I told ya, did anybody listen? Noooooooooooo:banghead:
This argument, complete with charts & graphs and "8 x 10 color glossy photographs" has gone on in professional and metalworking trade journals for years. Each side is well armed with credentials and opinions.
I think the debate over the benefits of cryo-ing a barrel will only be solved after we settle on the number of angels that can dance on the head of a pin.
There has been some excellent and authoritative information presented in this discussion without anyone being seriously injured.
If it's your barrel and you want the treatment, do it. If it helps, great. If it doesn't, it's not the end of the world.
Great thread, dudes.:evil:

[mete]

Charlie, why did you refer to cryo as "the new kid on the block", it's been around for 40 + years ?

[gun-fucious]

see the problem for the pure science dood is that they fail to believe that
when a barrel is super cooled in nitrogen, the little wee folk are better able to bless the steel

;)

heres what Gale had to say:

It seems that every time I finish a chapter in my book someone makes a post on my material.. I just finished this subject yesterday. I tried a controlled test in 1984 on cryo treated barrels. It was on S/S match Bench Rest barrels and it was for accuracy only. Results were negative. It did not help. A couple of years ago Lazzeroni did a comprehensive accuracy and wear test. The conclusion was accuracy negative but some improvement to wear. Before he did a release on the study he did the complete study again. This time the results were the exact opposite as the first test and the control barrel lasted longer. Conclusion Save your money!!!

[Detachment Charlie]

Mete:
Considering all of the other heat treatments (starting with charring the tip of a sharpened stick to make it a better hunting instrument for our cave-dwelling, mamoth-slaying ancestors, or running a red hot sword blade through a slave for quenching), the 40 year track record of cryo treatments makes it sort of the new kid on the thermal processing block.
However, if you include processes like H-I-P, then it's not the newest kid, but it's still no veteran. As this thread has shown, the beneficial application of cryo certainly isn't as well understood.
Oh, and the running-the-slave-through style of quenching has generally been abandoned, thanks to OSHA.:cool:

[Badger Arms]

Again the basics , to relieve stress atoms MUST MOVE. The ability of atoms to move is proportional to temperature , therefore you heat to stress relieve.When typical stress relief treatment call for 900F thats because it takes that temperature to get significant atomic movement to relieve stress.

Atoms do have to move to relieve stress. Perhaps you are overlooking the fact that all atoms move all the time with the possible exception of atoms at absolute zero. Now, when you freeze something to, say, 300 degrees below zero, the mass of the object is significantly lowered. When mass is lowered, atoms and grains are forced to allign with their smaller structure.

Here's the laymans concept I have. Let's say you have a box of "Lego Brand Blocks." Toss these blocks into a box so that they overflow. They are very stressed in this condition. If you kick the box, legos will move and change position. If you shake the box for a few minutes, the legos will settle down and be more stable the next time you kick the box and therefore won't move much. If you take a 2x4 and smack the legos down in the box repeatedly, they will be MORE stable and take up less room. This is what cryo does, if I can make that logical leap, it is the 2x4 that uses compression of mass to make a more stable structure.

Assuming there were stresses to begin with, this shrinkinging will "SQUISH" the atoms into a more dense structure breaking loose any internal stresses. When you then heat it up again, you are heating the matter at least 350 degrees or so and the object will grow perhaps one or two percent in mass. It therefore must have less stress. This makes sense to me, but I'm not an expert.

[Handy]

Badger,

That makes sense only if you remove the word "mass" in the first paragraph and substitute "volume". Nothing in this universe changes mass due to temperature.

[Badger Arms]

You are correct, sir. What's the proper word for SQUISH though?:)

[Barrelmaker]

Compression.

[skiwaterorsnow]

The attached links support cryo as having an effect on some metals. Most metals have atoms with bonds to other atoms. Why low temperatures affect the metals / atomic arrangement is not known but would make a good PHD thesis.



http://www.linde-gas.de/international/web/lg/de/likelgde30.nsf/repositorybyalias/cryoflex4/$file/Sub-zeroTreatment_final.pdf

http://www.springerlink.com/content/m44w2gn673112017/

http://www.wordquests.info/cryogenics-pt2.html