4340 isn't a carburizing grade, but 4320 is. 4340 is excellent for through hardening, and moderate for induction hardening. Perhaps you should provide more details about your application then we can more tips.
it is possible to carburize 4340 steel, i have experience up to .075 deep case., but is not fun to work with.
What I mean is that the core hardness is 50-55 HRc
so it needs special manufacturing procedures.
the effective case depth should be measured
visually because of the core hardness.
We have used carbonitrided 4340 for prototype broaches in place of tool steel with very good results. Carburizing or carbonitriding is used in large bearings successfully. The case depths I’ve seen run from .010 to .030 deep.
{b]EdStainless[/b],
It has been my experience that carbonitriding will normally give a much thinner case than straight carburizing. I would say that the thicker case as posted above would be possible though I don't see a need for the thicker case with the much harder core seen with 4340 unless you want to lower the core hardness.
Thanks for all the great responses.
We are manufacturing a forged crankshaft currently out of 8620, It uses needle bearings on the journals and are looking for a more fatigue resistant material.
Thanks again!
Since you are contemplating changing material have you looked at other material like Flexor that is supposed to have better torsional properties than 4340. You can also carburize it.
