Can a piece of 4140 gun barrel be hardened for a file trim die?

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  • Last Post 08 January 2021
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GBertolet posted this 07 January 2021

I want to make a case forming trim die for the 44 automag cartridge, from 30-06 and .308 cases. I have a lathe, and a 1" diameter rifle barrel stub. After I bore to .470, and thread to 7/8X14, can this steel be hardened enough to resist a file? I was planning to heat with an oxy/acetelyne torch, and quench in oil.

I had considered buying a 44 mag trim die, which is slightly smaller in diameter, and honing it out, but I wanted to try this first.

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Ken Campbell Iowa posted this 07 January 2021

stainless or chrome-moly ?

most CM gun barrel steels are in the 4xxx series, and are chosen for tough ... not hardenability with either heat and quench nor case hardening ... ... so pretty much a NO for file hardness ...

but if you only have 1 or 2 hundred conversions i would give it a shot with  " as-is " ... ...   just polish it really good.

also, tool steel is not really that expensive  ....  get green drill rod, not reamer blanks.  this can be machined at home and is flame-heat hardenable .

also, 7/8-14 pre-threaded cold rolled is available at your local Ace hardware ...  this is kind of strange stuff to machine ( take light final cut ) but is actually pretty wear-resistant as is .  i have expander buttons from stressproof " as is " that are 50 years and still working ...

hope this helps.  ken

 

 

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kootne posted this 07 January 2021

It will probably not get file hard quenched in oil, if it doesn't, quench it in water. I've made cutters that way. They can't be run at much speed as a cutter but they will be file hard. You'll never get enough speed on that file to pull the temper out the steel

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mashburn posted this 07 January 2021

When you heat the 4140 steel past the critical state(non-magnetic) and quench in oil it will be hard as glass and will break if dropped on a cement floor. it will definitely not be cut with a file. To make it useable you must temper or draw it out. By tempering I mean to heat to a specific temperature and quench again. The hotter you heat for the temper, the softer it will be and vice versa, the lower the quench temperature the harder it will be. After you harden the steel will be nasty black and you must polish it so that you can see the color when heating for the temper. You can pull up on the internet the heat by color of the steel and the  intended usage of the item. The inside of the tool will be nasty black and scaled. You will have to clean the inside out and the inside diameter will be slightly larger after the cleaning and polishing that it was originally. Have fun

Mashburn

Hello again,.

I was thinking of such steels as O1 and W1 and not 4140, when I wrote the above instructions. please excuse the goof up .But, if you were drawing O1 or W1 out for such hardness I would suggest about a 200  degree temper temperature. 

Mashburn

David a. Cogburn

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kootne posted this 08 January 2021

My experience says you won't get that hard with oil, so I googled it. 4140 maximum hardness as quenched with no temper is 51Rc. A good file will most certainly cut that, altho not nearly as easy as mild steel. I will stand by my recommendation to quench in water if you want it to resist file wear. I would also be surprised if it didn't shrink around the hole rather than expanding during the quench. If you do try to quench in oil, make sure you have a metal container (plastic melts) and deep enough to submerge the die at least a couple inches. I would recommend using something like hydraulic oil rather than old motor oil, it will cool better. Have a metal lid you can cover the quench bucket with in case you do set your oil in fire. I think the critical temperature for quenching 4140 is about 1450F and you can set oil on fire in a heartbeat if you don't get it well under the surface very quickly. You will want to keep it moving around in the quench to cool as rapidly as possible. I would suggest using a piece of soft iron wire (baling wire) through it and twisted into a loop. If you are heating with a torch, use a plier to hold the wire while heating and quenching. Then your pliers aren't a heat sink causing uneven heating (and ruining the temper in your pliers, if that is a concern). Try it and if the fie cuts it at all, redo it with a water quench. 

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Boschloper posted this 08 January 2021

4140 is .4% carbon for hardenability plus chromium and molybdenum for toughness. Files are usually 1095 which is .95% carbon. You will never get 4140 as hard as 1095. You might try a case hardening compound like "Cherry Red" (rosemill.com).  These products increase the carbon content at the surface for a very hard, wear resistant surface. If you degrease the part really good (and I mean really good), you can temper it in the kitchen oven at 200 deg F for 2 hours and remove a lot of the brittleness with only a slight reduction in hardness.  If you don't degrease the part really good you will be sleeping in the dog house for a long time. Trust me on this. 

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mashburn posted this 08 January 2021

Hello Ken,

I have used that same threaded rod that you spoke of, Like you say it works very well

Mashburn

David a. Cogburn

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