Heat treatment of 4140 annealed

Jerry · Aug 31, 2006

Will heat treatment distort 4140 after machining is finished? Where would you send it if you have no heat treat facilities. I am located in IL. Any suggestions?
TIA
Jerry

cruzinonline · Aug 31, 2006

Are you heat treating to stress relieve or I'm assuming your treating to harden. In either case it's been my experience it will move. We always leave excess stock to finish grind any precision fits after we harden. Course if your making a chisel it won't matter much.

Jerry · Aug 31, 2006

No its not a chisel!! Its a rimfire bolt action body. I am afraid I will just have to case where the locking lugs are and call it good. I am afraid it will banana at the ejection port.
Thanks for your reply cruz
Jerry

johnoder · Aug 31, 2006

4140 is not great stuff to be case hardening.

John

solomon63 · Aug 31, 2006

I cut some parts from prehardened 4140. I think it was about rockwell 35 or 40. I like receivers like the sound of an m-14 when the bolt closes. Rings like a bell to my ears. I don't know what rimfire you are making but some of them are not too hard.

blackboat · Aug 31, 2006

Jerry, Sounds like you're a little further along than me, but I'm also working on a rimfire action. My solution has been to just chew it out of 4140 pre hard. Something like 30-35C so not bad.

IIRC, I believe it was Alan Hall's prototype for his rimfire that was made from annealed and just left that way. Has apparently been used a good bit and supposedly shows no wear to be concerned about. Haven't seen Alan in awhile since my match schedule has been curtailed due to illness and lack of funding, otherwise I'd ask him. Could be confusing a the story with Flash Ebert's Turbo action development though.

Anyway, good luck,
Rob

Jerry · Sep 1, 2006

4140 is not great stuff to be case hardening.

Thanks for the post John, but why?

Jerry · Sep 1, 2006

Blackboat
email me about your project. Would be good to hear about others ideas.
Jerry

Yogesh · Sep 1, 2006

Heat treat under vacuum, costly but nigligible dimensional or shape distortion.

johnoder · Sep 1, 2006

Thanks for the post John, but why?

Already has ample carbon content to be directly hardenable. Case hardening (or carburizing) is a process that involves even higher temperatures than are used when direct hardening 4140. The intent of the process is to add surface carbon to low carbon steel, so that surface can be directly hardened. Case hardening 4140 does not add much carbon to the surface, but does in fact subject the steel to higher temperatures than you would have used to directly harden 4140. Since you are interested in absolutely mimimal distortion, higher temperatures are definitely the wrong approach. Should you be persistent enough in your case hardening efforts to add surface carbon to 4140, you are asking for considerably less toughness from this really great, tough steel.

There are a few reasons for you

John

scraper · Sep 1, 2006

try paulo in st louis

Jerry · Sep 1, 2006

There are a few reasons for you

thanks for your help
Jerry

Forrest Addy · Sep 1, 2006

4140 will air harden to a certain extent depending on the section thickness and the ambient air. For a rifle bolt, I'd suggest heating it to 1500 to a good red and then suspending it from wire or holding it in tongs play compressed air around the locking lugs until it's black then to quench and cool enough to handle.

The cooled portion will be RC45 and the balance will be RC 35 or so but check it on a tester. This is firearms not horseshoes.

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