In an AK receiver there is a small part called the ejector. its a 1mm thick tab, approx. 10mm square before it bend with the wall geometry.

It needs to be the hardest part on a rifle due to repeated strikes against a brass bullet casing. Many poorly built AK's fail due to mushrooming on the ejector. Some builders simply water quench w/o any temper except the 350F paint oven.

Would i be better off doing a cryogenic treatment after quench? I don't believe there will be much retained austenite with 4130, however i'm worried about this thing shattering due to untempered martensite. I'm looking for 50Rc.

Thanks, TWISTEDNECK.

Cryo will have no effect on 4130. The 350F will barely temper it , I'd like to see 400 F. With a small part you should have about 50 Rc.

Thanks mete, i'll make sure to not exceed 400F on the temper.

Regarding the untempered martensite, would there be a potential brittle fracture mode that the 400F will help remove?

Actually this is low carbon martensite and you can get away with a few things but there won't be much difference in hardness between 350 and 400F. I've always found 400 to be a minimum I'm happy with and it's a typical industry temperature.