What is heat treating an action?

[ascast]

[SIZE=3]Just for discussion[ - what is actually being done when an receiver is heat treated? Is this commonly done while case hardening; at the same time. I understand that it is to relieve internal stress from forming or imparted during machining. Also to change the metal structure at the molecular level somewhat. Case hardening is to harden the outer surface by heating so that it absorbs carbon. The flip side question is- what happens when a receiver goes through a house fire? And furthermore, an action for a 1800's black powder rifle should probably not require as much consideration as a modern high power rifle. just wondering, I keep finding old actions that went through fires./SIZE]

[john.k]

Its quite a complex subject...I recall at one time gearbox gears were being toughened by freezing in liquid gas .......I think it was the New Process box used in Dodge small trucks.

[414gates]

The process of annealing is to hold metal at a fixed temperature for a long enough time for the crystal structure to re-grow. Annealing is a softening process for metals, when the crystals re-grow, they are no longer under any stress or strain.

1. annealing of steel is at 1500 F
2. a typical house fire reaches 1100 F

Assuming the receiver is steel, a house fire won't soften it up.

Case hardening is a different process altogether, and is done after annealing.

All steels can be annealed, not all steels can be case hardened.

[uscra112]

1. annealing of steel is at 1500 F
2. a typical house fire reaches 1100 F

Assuming the receiver is steel, a house fire won't soften it up.

Case hardening is a different process altogether, and is done after annealing.

All steels can be annealed, not all steels can be case hardened.

Not true. 1100F will definitely draw the temper of hardened steel in just a few minutes. Small parts like triggers and sears are especially vulnerable.

This isn't a simple subject. There are engineers whose entire career centers on how steels are heat treated, to the exclusion of all else. They tend to have advanced degrees in Chemistry.

Buy and read repeatedly:
https://www.amazon.com/Heat-Treatmen...%2C1920&sr=8-3

Or if you want to spend the money for the Masters Degree course:

https://www.amazon.com/ASM-Handbook-...%2C1920&sr=8-6

[414gates]

Not true. 1100F will definitely draw the temper of hardened steel in just a few minutes.

Temper and anneal differ are different processes, one does not replace the other, although the results are confused with each other.

A temper is a stress relief, which depending on the steel can start at 500 F.

The general opinion is that when you apply heat to metal, you anneal it. It is incorrect. An anneal is a very specific operation, it is time specific and temperature specific. Time is very important because metal crystals don't grow instantly.

This idea of heat being an anneal is carried forward from the heating of brass case necks, which is incorrectly called annealing. it is not annealing, it is stress relief.

[uscra112]

Tempering is not stress relieving.

[beechbum444]

This topic gets me thinking every time a I a rifle or action on an auction site that has been in a house or cabin fire

[414gates]

Tempering is not stress relieving.

https://www.britannica.com/technolog...ing-metallurgy

"The process has the effect of toughening by lessening brittleness and reducing internal stresses."

[Scrounge]

Not true. 1100F will definitely draw the temper of hardened steel in just a few minutes. Small parts like triggers and sears are especially vulnerable.

This isn't a simple subject. There are engineers whose entire career centers on how steels are heat treated, to the exclusion of all else. They tend to have advanced degrees in Chemistry.

Buy and read repeatedly:
https://www.amazon.com/Heat-Treatmen...%2C1920&sr=8-3

Or if you want to spend the money for the Masters Degree course:

https://www.amazon.com/ASM-Handbook-...%2C1920&sr=8-6

The problem with your first reference is that it is around 100 years old. There has been a LOT of water under that bridge. If you're making parts for an old boys rifle, it's a great reference! if you're working with modern alloys, not so much, so you need more modern references. Your second reference is probably available at your local library in the Reference section, but you can get a lot of the info there from these folks: https://archive.org/search.php?query...mpering&page=3 Down the page a bit is the Workshop Practice Series book #1, Hardening, Tempering, and Heat Treatment for Model Engineers. It's only 30 or 40 years out of date, and written for British model engineers, but is a good treatment of the subject for amateurs. I doubt it mentions cryo treatments, though they've been around for a while, but I'm too lazy to look at my paper copy. Good thing about Archive.org is that most of what they have is readily downloadable in multiple formats. I've got gigabytes of stuff from them. They have several collections and the one I like the most is probably the https://archive.org/details/folkscanomy Library of Books. There are subsections on Defense, and Engineering that I've ravaged pretty thoroughly, but also look at the Public Library of India, and the American and Canadian libraries. Some of the newer books are only available to borrow, and that hasn't worked well for me.

[Scrounge]

Temper and anneal differ are different processes, one does not replace the other, although the results are confused with each other.

A temper is a stress relief, which depending on the steel can start at 500 F.

The general opinion is that when you apply heat to metal, you anneal it. It is incorrect. An anneal is a very specific operation, it is time specific and temperature specific. Time is very important because metal crystals don't grow instantly.


This idea of heat being an anneal is carried forward from the heating of brass case necks, which is incorrectly called annealing. it is not annealing, it is stress relief.

Also depends on which metal you're talking about. You anneal copper (and copper alloys) by getting it red hot and quenching in water. Higher carbon steels will harden if you do that to them, and depending on the alloy may well crack. Tempering is adjusting the hardness of steel, not stress relieving it. It's done after quenching, to get the hardness where you want it. If you do not temper, you risk shattering the steel, as it can get glass hard.

Case hardening is increasing the carbon content of a thin layer of of the iron surface, and hardening that. That thin layer is the "case." The core remains whatever it was, and done to mild steel, it leaves a soft core with a hard case on the outside. It's used for adding wear resistance, and decoration as in color case hardening, while retaining a softer and less brittle core. See any of the books recommended above, not just the ones I mentioned.

[Der Gebirgsjager]

Speaking as a gunsmith (Ret.) only, not having a degree in a metallurgic science, I can only tell you that in the real, practical world it is a case by case basis as to whether or not a gunsmith will work on an action that's been through a fire. The feeling is that if the action was heated for a protracted period it may have "drawn" to the point of being dangerously soft, and if it was subjected to extreme heat it may have changed its carbon content and become brittle.

I did work on restoring and refinishing two pre-WW II Win. Mod. 70s that belonged to a neighbor. The stocks were charred, but salvageable, and the metal showed no discoloration. They had belonged to his dad who had them secreted between the folds of a mattress stored in the garage. When the house caught fire the mattress was burning but not fully engulfed in flames, and the fire dept. hosed it down with water, which probably did more damage than the fire as they were thoroughly rusted.

But when someone presents you with a rifle or handgun that has had the wooden stock or grips completely burned off, you can pretty well bet that it got pretty hot! A gunsmith will want to know the entire story in as much detail as possible as pertains to where the guns were in the fire and how long, and bearing liability issues in mind will usually refuse to work on them. Heat treating is a more or less exacting science, and the temperature and for how long is well known for most gun steels. Gunsmiths routinely harden small parts that they make in their shops, and draw the hardness back as needed to avoid brittleness, but when the gun has been through a fire the equation changes, and it's usually wise to avoid working on them.

DG

[Scrounge]

Speaking as a gunsmith (Ret.) only, not having a degree in a metallurgic science, I can only tell you that in the real, practical world it is a case by case basis as to whether or not a gunsmith will work on an action that's been through a fire. The feeling is that if the action was heated for a protracted period it may have "drawn" to the point of being dangerously soft, and if it was subjected to extreme heat it may have changed its carbon content and become brittle.

I did work on restoring and refinishing two pre-WW II Win. Mod. 70s that belonged to a neighbor. The stocks were charred, but salvageable, and the metal showed no discoloration. They had belonged to his dad who had them secreted between the folds of a mattress stored in the garage. When the house caught fire the mattress was burning but not fully engulfed in flames, and the fire dept. hosed it down with water, which probably did more damage than the fire as they were thoroughly rusted.

But when someone presents you with a rifle or handgun that has had the wooden stock or grips completely burned off, you can pretty well bet that it got pretty hot! A gunsmith will want to know the entire story in as much detail as possible as pertains to where the guns were in the fire and how long, and bearing liability issues in mind will usually refuse to work on them. Heat treating is a more or less exacting science, and the temperature and for how long is well known for most gun steels. Gunsmiths routinely harden small parts that they make in their shops, and draw the hardness back as needed to avoid brittleness, but when the gun has been through a fire the equation changes, and it's usually wise to avoid working on them.

DG

I sure won't argue with you on that! I'd lost track of the OP's interest in firearms that had been burnt. On an original 1800's gun it might not matter at all, since the steel was likely pretty soft to start with, but I'm a ham-handed, thumb-fingered amateur, not a gunsmith. I do keep thinking of a GSO in my collection that I bought in Turkey, when I lived there. It has what I think is an authentic antique flintlock, but the "barrel" is a piece of water pipe filed to resemble a gun barrel. There is no breechblock, either. I've considered building a barrel for it, as the stock and lock are beautifully made, but I think it would need to be 36 caliber at most for the size of the barrel channel. A .22 caliber barrel might be better still!

Bill

[M-Tecs]

Some good info on this thread and some not so much.

As stated this can become a very complex and detailed issue depending on application and materials.

That being said generalizations can be used too provide a fairly accurate overview for firearm applications.

There are two basic groups of ferrous based metals in regards to heat treatment and heat treatment is different depending on carbon content. Low carbon steels are steels like 1020 or 8620 that lack enough carbon to be hardened through heat treatment without the addition of more carbon. That process is referred to as case hardening. During this process various methods are used to increase the surface carbon content. Depending on the process and time this may be only a .001" or .002" deep or much deeper. I have seen case a deep as 3/16" on gears.

With medium or high carbon steels no addition carbon is required and hardness is generally all the way through the material not just on the surface like case hardening. The material temperature is raised until the material become none magnetic. A magnet is used in torch or forge heat treating. More sophisticated methods use ovens and temperature charts and sensors. Once the material has reached temperature and stabilized it is quenched. Quenching medium could be water, oil or air depending on material. At this point the material is full hard and may be to brittle for some applications so the next step is tempering.

Tempering occurs after HT. It is nothing more than raising the material to a specific temperature or color to provide the proper balance of hardness verse toughness for the specific application. With some steels that can be as low as 400 degrees Fahrenheit.

Annealing/normalizing is process that has various meaning for various application. For the ferrous HT process is generally means heating and slowly cooling to get the material to it's softest stress free condition possible. While annealing/normalizing may be used in the manufacturing processed in firearms it has little application for firearms users/gunsmiths outside of manufacturing processes. Brass is a different application and annealing necks has a great benefit.

As to firearms in a house fire that is case by case. Some older firearms are low carbon and not affected. Most modern firearms do have some form of HT and a house fire can affect them. Rule of thumb is if the wood is burnt off and or the spring are soft the firearm needs to be reheat treated. If the metal has scale on it needs to be HT'ed or junked There are only a couple of companies that still do this the last time I checked.

Some basics here:

https://learnmechanical.com/heat-treatment/

https://www.machinemfg.com/heat-treatment-processes/

https://pediaa.com/difference-betwee...and-tempering/

[uscra112]

@scrounge: Only guns I know of that can certainly survive a fire are cheap 19th century relics like the Stevens 44s I collect. No high carbon steel in them at all, except for springs. Receivers are malleable iron. Everything case hardened. (And they stayed that way right up to WW2, too! Never were brought into the 20th century.)

[Mal Paso]

I had 1 1/8" jackhammer steels that went through a house fire. They looked OK but did not survive first use. The shank broke off and the end had peened so badly the hammer had to be disassembled to remove it.

[john.k]

It often claimed that if springs are still springy,then the gun is OK.....This doesnt take account of the hardened contact surfaces in the trigger and firing mechanism,and these surfaces fail quickly from deformation if softened........parts like a barrel are often tempered at 600DegC ,and can be OK after much higher heat than collapses springs.

[James Wisner]

Guns that have been thru a fire, that is a WIDE variation of damage

In the past 52 years I have been Gunsmithing I have seen the good and the BAD

One fire the rifles were stacked up in a corner, so when the roof came down it protected most of the rifles.
The barrels were bent and useless, the front half of the forearms were burnt to a crisp, even the front scope bells were melted.
The actions were not damaged
One was a Savage 99, the work was to replace the barrel, a new forearm, a new scope, reblue the metal, refinish the butt stock and it went back to the customer.

Bad ones.
Any time you see scale on the metal, do not bother with it.

They figure that carbon migrates into the steel at .008" per inch at 1500 DF, this is from the flip side when you are Case Hardening

I have seen many guns with .015" scale on the metal.
I also understand that with all the free HOT carbon in a fire zone you can get a rough idea of what is going on with the metal when the fire is that hot at that time.
By the time you get the scale off you have lost most of the fitting required between the parts, plus depending on the metal it will have to be Carbon Restored, Quenched and Tempered, if an alloy.
Or Case Hardened, and Tempered if it is a mild steel

Example a Remington M700 receiver is made from pre-hard 4140 which is about 38 - 40 RC, the bolt will be roughly 5 RC points harder

While a Winchester 1892 or 1894 receiver built before WW1 would have been made from roughly 1025 - 1030 steel and would be about 28 - 32 RC in hardness

My 2 cents worth
Jim Wisner

[uscra112]

Rem 700 receivers were made from prehard? I knew they were made from tube, but that fact has somehow escaped me.

[bigdog454]

What m-tec rote id good info. I worked in a tool and die shop for years, and one of my duties was the heat treatment of the dies that needed so. to heat treat a metal you need to know the alloy of it. You get that from the metals vendor or metals foundry. I have an engineering degree and was certified to do heat treating, I would not attempt to heat treat an action without a lab result first.

[john.k]

heat treaters would often get the gearset out of a truck axle to reharden......these attempts would inevitably leave the customer $1k out of pocket after the heat treat and new bearings for the diff.........the gears would fail in under five thousand miles.........I once bought a excavator gearset from a burnt machine.......was the only one available on the planet......I warned the owner to trade the machine ,..... once it was going ,he assumed it was good........not so,whole gearset failed again within six months ,exactly as I had said........burnt set cost $10k,he had to go new ex Korea for an uprated assembly ,cost $60k plus fitting..........the excavator was a Samsung ,and worth maybe $50k to a newbie or a farmer.