What is heat treating an action?

[M-Tecs]

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.

That would be from the heat treaters not using the correct process. Medium and high carbon steels can be damage by too high of temperatures and or too long of soak times. Once the carbon is burnt out the part is basically scrap. Most larger gears are case hardened and respond well to re-case hardening even if the case hardened layer is worn off or had the carbon burnt out. As simple heat and quench without inducing carbon does very little to nothing.

some interesting reading here

https://gearsolutions.com/features/h...vy-duty-gears/

https://gearsolutions.com/features/h...ment-of-gears/

[uscra112]

Medium and high carbon steels can be damage by too high of temperatures and or too long of soak times. Once the carbon is burnt out the part is basically scrap.

As witness the infamous story of the low s/n Springfield 1903 receivers.

[M-Tecs]

As witness the infamous story of the low s/n Springfield 1903 receivers.

There are still differing views on this issue. The early pre-nickel steel 1903 were case hardened.

http://m1903.com/03rcvrfail/ Too long to post but somewhat a different take than Hatchers had.

https://www.tapatalk.com/groups/coll...ers-t2622.html

The subject is discussed and cussed frequently; it is always contentious enough to provoke some heated and emotional debate.
The Army considered taking the "low numbers" out of service, and even generated a few policy documents to that effect, but the policy appears to have been largely ignored. The sea services (USN, USMC, USCG) had no such policy and kept their low numbered rifles in service until they were replaced by more modern rifles.
Sometime in the late 1950's, an NRA member wrote in to "Dope Bag" and asked pretty much the same question you did. This is the response, quoted in its entirety:
"I have been told of low numbered Springfield rifles which may be dangerous, though the reason is not clear. What is the fact on this matter? ~ A.R.A.
Answer: Before World War I, Model 1903 rifles manufactured at Springfield Armory and Rock Island Arsenal were made of carbon manganese steel, casehardened. A few of these rifles in service suffered burst receivers or broken bolts from high pressure or other abuse.
In 1918 the heat treatment was changed at both Springfield and Rock Island and this greatly strengthened the receiver and bolt. The new double heat treatment went into effect at about rifle No. 800,000 at Springfield and at about No. 285,507 at Rock Island. It is practically impossible to burst a receiver or break a bolt of rifles with serial numbers above those, though with soft cartridge heads or dangerous pressures failure of the cartridge case can permit enough gas escape to splinter the stock or bulge the magazine and endanger the eyesight of a shooter not wearing shooting glasses.
At No. 1,275,767 Springfield Armory changed the material in the bolt and receiver to nickel steel. At No. 319,921 Rock Island began using nickel steel for some of its receivers but continued with the improved heat-treated carbon manganese steel for others. The nickel steel receivers were marked NS on the front face but this mark is covered by assembling the barrel to the receiver and the only way to tell the difference is by a file test. The carbon steel receivers are hard on the surface and can scarcely be filed at all, but the nickel steel receivers are fairly soft on the surface and the file will take hold. Nickel steel receivers and bolts are very nearly as strong as the double heat treated ones. The double heat treated receives and bolts are considered somewhat the more desirable, because their hard surfaces allows easiest bolt manipulation.
During World War II, M1903 and M1903A3 rifles with serial numbers over 3,000,001 were made by Remington Arms Co., Inc. and L.C. Smith & Corona Typewriter Co. Their receivers and bolts were made of high strength steels, and all these are considered high number rifles.
As to safety, there were about 800,000 low number M1903 Springfields and 285,000 Rock Islands made, or over a million in all, and they were continued in service until superseded by the M1 rifle. From 1917 to 1929 inclusive, records were kept of all accidents to receivers of Springfield rifles, and during that time of the 800,000 low-numbered Springfields there were 33 reported as burst or about 1 in 24,000. Of the 285,000 Rock Island receivers there were 24 reported burst or about 1 in 11,800. There 9 cases of severe injuries; no one was killed, and in most cases the there were no injuries or only minor ones. From the above, the user of one of these rifles can judge whether or not he cares to continue firing it. The chance of an accident does exist although it is slight.
During all those years there was no reported case of any receiver burst or bolt broken in any rifles having serial numbers higher than Springfield 800,000 or Rock Island 285,507. [Ed Note: This is not true. There is at least one case reported in Hatchers Notebook of a Springfield receiver numbered above 800,000 that burst when a 7.92 x 57 mm cartridge was fired in it. RLS]
Springfield Armory investigated reheat treating low-numbered receivers and officially reported that reheat treating them would not guarantee safety. This was because failures were generally due to burnt steel from overheating while forging, and burnt steel cannot be restored by any known method short of remelting. ~ J.S.H."

[lar45]

Heat treating is a rather large and complex subject.
I'll try to cover a small amount from the knife making, or small gun parts point of view. This should not be applied to the action!
If the heat treatment of an action is not done correctly it can kill you.

Here is a TTT Diagram for Eutectoid steel.


https://materials-today.com/ttt-diagram-of-steel/

If you take a piece of simple high carbon steel such as 1080 or 1095, and heat it up high enough the grain structure will turn into Austenite, this is generally a little bit above where the steel will not be attracted by a magnet. For specific temperatures and times, look at the chart for the steel you are working with.
On the chart, you will see a big sideways curve, this is the Pearolitic nose.
From Austenite you can change the grain structures and properties of the steel into several states depending on how fast or slow you cool the steel, or if you cool and hold at a specific point.
To make a knife or hard gun part, you heat to Austenite, then cool the piece fast enough to beat the pearalitic nose of the curve.
Saltwater cools faster than water, water cools faster than oil...
If you cool fast enough the steel transforms into Martensite. The grain structure is very small with sharp corners. This is very strong, hard and can be brittle. To get rid of the brittleness while still keeping most of the strength and hardness, you need to heat it up some and "Temper" it. Heating will start to round off the corners of the grains, this will increase flexibility and decrease hardness and strength just a little bit. The longer you heat it, the rounder the corners will get. Heat it long enough and the grain size will start to grow.

From a knifemakers point of view, take a piece of 1095, heat to Austenite, quench in water and break it. Clamp it in a vise and bend it with a crescent wrench. You will have a very hard and brittle piece of steel with a very fine grain structure.
Now do the same heat and quench with a second piece of 1095. This time we are going to temper it. Place in a 400F oven for an hour. Then bend it. It should flex more than the first piece, then break if you lean on it hard enough. Heat it for another hour and it will flex even more, but you only loose a little bit of hardness and strength. You now have "Tempered Martensite ". This is a good thing for a knife or small gun parts.

I saw part of a barrel from an 03A3 that had been heated to take the front sight off, then quenched in water. When it was shot, it fractured and blew the end of the barrel off.

Sorry if I rambled a little, I got distracted a couple of times...

[John Taylor]

With most fire damaged guns I look at the springs. If the spring no longer has tension or has lost form the gun got hot enough to effect the heat treat, usually 700 to 800 degrees. On the 1903 Springfield I read someplace that they did not have a temperature controlled oven until about 800,000. Going by the color for heat treat the guys during the day would not see red as early as the guys at night. So the actions quenched during the day were a lot hotter than the ones quenched at night. I don't know how true this is but I found out while heat treating small parts that if the quench water is cold the part can become more brittle and sometimes split or brake. I use oil for quenching springs which helps a bunch.

[lar45]

I was making a pry bar out of a potato digger chain link years ago. I got it hammered out, bent just right and ground perfect. I then heated to red and water quenched. I tapped it on the anvil to hear it ring and it shattered like glass. I made another, quenched in oil this time and it's been working great for 20 years.
This was all before I went through engineering school and took some metallurgy classes...

[uscra112]

John,. that story comes right out of Hatcher's notebook.

[john.k]

A common trick was to quench in water with 1/8" layer of oil on top..this gives a tough quench without filling the shop with smoke.

[john.k]

The local heat treaters used to have a big sign up at the front counter "Satisfaction NOT Guaranteed."..........they were con artists too,and would never say when something was bound to fail........I once took the endplates from a big hydraulic motor to be 24hr nitrided.........on picking them up , a woman grabbed me outside ..."We had that same part nitrided last week,and the big part didnt harden,only the small part".....so they could have said that wont work on the 200lb part......but they charge nitriding by the pound.

[M-Tecs]

A common trick was to quench in water with 1/8" layer of oil on top..this gives a tough quench without filling the shop with smoke.

Why the oil if it's a water hardening steel? If it's an oil hardening steel the 1/8" of oil will do nothing and the quenching will be way too rapid for oil hardening only steels.

I've never used this method personally but I do have some knife making friends that tried this method using 2 inches of oil on the surface. They weren't overly impressed and gave up on it. That was shortly after they read about it here:

https://www.bladeforums.com/threads/...quench.589042/

On the industrial side they take great pains to keep water out of the oil. The quench tanks are generally heated to specific temperature for specific materials. Even the type of oil determines the results. HT's oils have specific quench rates from fast to slow. In certified HT shops the quench oil normally is heated between 120 degrees & 160 degrees depending on material. I mostly kept my quench tank at 120 degrees.

Some examples of what's available here:https://forgingworld.com/what-is-the...quenching-oil/

Some water in oil issue here:

https://www.houghtonintl.com/sites/d...uench_oils.pdf

https://www.houghtonintl.com/sites/d...er_removal.pdf

https://gearsolutions.com/department...e-problematic/

https://www.globalspec.com/learnmore...eatment_fluids

https://www.machinerylubrication.com...st%20Apparatus

[todd9.3x57]

what it comes down too, is whether you trust the true gunsmith (not a shade tree gunsmith either, hey wait a minute, i am a shade tree gunsmith) or do you trust google?

i'll trust the true gunsmith. i don't trust Wikipedia or google.

[M-Tecs]

what it comes down too, is whether you trust the true gunsmith (not a shade tree gunsmith either, hey wait a minute, i am a shade tree gunsmith) or do you trust google?

i'll trust the true gunsmith. i don't trust Wikipedia or google.

None of the people (true gunsmith whatever that is) or sources you listed what would be termed as subject matter experts on heat treating. There are exceptions like Doug Turnbull, Bobby Tyler and a couple of other "gunsmiths" that I would trust. I would be willing to bet 99% of the gunsmiths only know enough machining and or heat treating to just get by if that. I trusted certified heat treaters that adhere to AMS or SAE standards.

Heat treating started as an magic followed by art. Today it is 100% science and 100% repeatable and predictable. Until Clinton/Gore eliminate the mil. spec. standards the information was cheaply and readily available. That info is now controlled and sold by either the SAE or AMS. The info is no longer readily available or cheap anymore.

The USAF/NAVAIR Technical Order 1-1A-9 is still available and good reference https://www.robins.af.mil/Portals/59...-03-094319-467

Certified Heat Treaters will adhere to the SAE AMS2750 to ensure their equipment is properly calibrated.

Firearms are very old technology normally designed with significant safety margins made out of material that are fairly tolerant of marginal heat treat processes. History is filled with HT mistakes that lead to catastrophic failures.

[JackQuest]

Tempering is not stress relieving.

Agreed; tempering is not stress relieving. It is actually inducing a certain level of stress based on alloy, highest temperature reached during heating, quench temperature, quenching fluid (water, various oils, et.cet.) and quench duration (overall cool down).

Also, annealing does not remove all stress. The size and placement of alloying elements (chrome, nickel, vanadium to name a few) create interstitial defects in the crystal structure of the overall metal object. These usually toughen the metal against the movement of cracks in the overall alloy.

As noted above, heat treatment, tempering and annealing are all different but related to each other. To throw a wrench into everything, there is also the Fermi temperature of the alloy. This is the point where the metal loses any ferro-magnetic properties (being attracted to magnet). LAR45 speaks to this above. If you watch the guys making knifes on TV you see them test the heated steel with a magnet to make sure they are above the Fermi temperature before quenching. The gasps of horror come when the knife maker quenches in water and not oil.

[Scrounge]

@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.)

IIRC, my "collection" of rifles numbers 6, three of which are Stevens boys rifles. I have one early model Favorite that I believe is an 1884 or thereabouts, in .22LR, a 1915 Favorite in .32 RF Long, and a #26 Crackshot in .32 RF. Those, and the 1903A3 National Ordinance action frankengun are the only ones I'll be doing any "gunsmithing" on. Do not intend to mess with heat treating or case hardening. Don't know how it shipped, but the .22LR Favorite my dad bough when he was a young teen, broken, and he bubbaed it to work well enough that all the older 6 of my brothers and sisters learned to shoot with that rifle is all white metal now, and has been as long as I've been using it. Call it maybe 63 years... I've replaced a couple of screws, and will be fitting a new extractor one of these days, but keeping all the bubbaed parts for the history. The two youngest sisters didn't ever get to shoot it, as (I learned a couple of years ago) the screw for the lever that dad brazed a head and hand filed to shape stretched enough to no longer lock up the action. We thought it was shot out for 20 or 30 years. Nope, not yet. The other two are project rifles I bought from another member here. I need to card the rusted actions, and then steam them to see if I can get some blue on them, make CF breach blocks for them, and finish forming up some brass I've bought. Will also be making dies and such to keep reloading for them, and re-make more brass, and I won't be disposing of the original RF blocks. I'd say "cheap 19th century and earlier relics..." The rifles Jonathan Browning was making in the 1830's were made in his blacksmith's shop of, probably mild steel at best, and if I ever managed to lay hands on one, I wouldn't muck about with it at all, but anything similar and unmarked might be fair game for my practice pieces. I will never be a real gunsmith. But I'm happy tinkering with low value weapons.

[uscra112]

The first Favorites were the "sideplate" models, produced in 1892 and 1893. Then came the "1894" model with the one-piece receiver, which was made almost unchanged until 1915.

Stevens receivers were always made of malleable iron. Not heat treatable in the sense that steel is, and they still contain enough carbon thaT they can't be fusion welded, because the carbon goes back into solution making the metal very brittle. Repairs have to be brazed.

[john.k]

Malleable iron wont be hurt strengthwise if it isnt melted .............the modern equivalent of malleable is SG or Ductile iron......same result by a cheaper process......some years ago there was a craze among heavy equiptment manufacturers to make big parts of ductile iron.......for instance Case made front axles ,loader parts,and main backhoe pivot castings.......if these parts had a breakage ,you had to buy a new replacement.......even Caterpillar got caught up in the craze....but the big buyers of fleets wernt happy at high maintenance costs caused by non repairable parts.

[uscra112]

I just took possession of mu latest Gunbroker folly, an early 1915 Favorite that Bubba had "color cased" with a welding torch. Sometimes called "fire blued". As noted above, it won't have hurt the receiver any. It'll stay that way until after I have it rebuilt. If the gun shoots, I may have it color cased for real, even though 1915s never were.

[Geezer in NH]

Colorcase by watercolors was a course offered on the Double Gun Jornal by Oskar Gaddy at one time more than a decade ago as a JOKE.

99.9% of firearms in a house fire where the wood was burned off are scrap. My shop did fire restoration the fire atmosphere damaged guns. Best that can be done is bead blast and re-blue, if the springs were not springs the gun is scrapped. Pushing it is not worth the cost. Sorry