I am working on a .50 cal project, and I have the receiver ready to heat treat. The receiver is made from 4140, and I plan to carburize it.

What hardness (Rc), and what case depth should I shoot for?

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Buck,

Could you explain why you want to carburize 4140 ? A very common receiver steel it's usually HT'd to about 40-45 HRc. I would certainly harden the core ,if carburized , to that hardness.Carburized to get more wear resistance of the surface would only need a thin case perhaps .010" to the .60 carbon level. You could also use something like 4118 or 8620 and go for a slightly deeper case.

quote:

Could you explain why you want to carburize 4140 ? A very common receiver steel it's usually HT'd to about 40-45 HRc.

40-45 is what I did with the other components, but my thinking was that the carburized receiver would be less likly to blow-up in my face than a through hardened receiver.

Please correct me if I am wrong.

Buck,

If I knew my receiver was AISI-4140, I'd thru harden and draw it to 38-40 Rc and be done with it!

However I'd have had the bar hardened prior to machining to prevent warpage and potential cracking in heat treat.

40 Rc is not at all difficult to machine.

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Originally posted by Buck3:
I am working on a .50 cal project, and I have the receiver ready to heat treat. The receiver is made from 4140, and I plan to carburize it.

What hardness (Rc), and what case depth should I shoot for?


Buck,

I would be very cautious about soliciting advice pertaining to heat treating gun actions from the "World Wide Web". Mete happens to be one who's advice I would listen to as he IS a metallurgist by trade.

But you will, or, should ultimately hold off making a decision until you talk to the company who you plan on hiring to do the heat treating. After all they are the ones who will have to stand behind it. Good luck!

A carburized roller bearing is hardened in the core to about 25-30 HRc ,the surface about 60.The steel is a .10-.20 carbon alloy.Hard surface ,soft center.Old Mausers were just carburized low carbon [little alloy].4140 [if you want tougher use 4340 !] HT'd to 40 HRc will give you about 185,000 psi tensile strength and good toughness. If you have a problem with that you have a design problem not a steel problem !! I hope you make it with reasonable inside radii -no sharp corners.

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I hope you make it with reasonable inside radii -no sharp corners.

good advice.....and that's why one might be far better off prehardening the material prior to machining......assuming this is an option!

Thanks for the advice. I think I will now heat treat it to 40-45 Rc. I can’t afford to shoot it enough to wear it out, so my main concern is the strength of the receiver. The material was prehard 4140 (28-32 Rc) so hopefully it won’t move around on me much. I used .03-.06 radius in all corners. I also will have it checked for cracks after heat treat.

Thanks,
Buck,

Buck unless you have a marginal design strengthwise you can probably use your receiver as is. It is already harder than most M98 receivers and it is hard all the way through.