Carburize depth/hardness

[Engparts]

I am working with some large thin walled rings. Material is AMS 6270 being carburized to meet effective case depth of .025-.035 before finish and .010-.025 after finish. Hardness is called as "case 15n 90 min" and "core RC 20-48"

If case depth was .035 with hardness of 15N 91, then ground to remove .025 leaving case at .010, what could I expect the hardness to be? How can the hardness of 15N 90 min be controlled for the full depth of case?

 

[TVP]

I'm not sure how familiar you are with case hardening and subsequent hardness measurements, so here is a figure showing hardness vs. depth below the surface of a case hardened part:

http://www.struers.com/resources/elements/7/250422l.jpg

In this example, the surface and near-surface hardness is ~ 760 HV (~ 62.5 HRC or 91.2 HR15N) and the effective case depth (term used by SAE J423) or case hardened depth (term used by ISO 2639) is 0.95 mm. For your specification, the effective case depth is 0.635-0.889 mm and the near surface hardness is supposed to be 90 HR15N (~ 690 HV or 59.7 HRC). This means that you will need to control the near surface hardness depth (plateau region) very carefully in order to have sufficient hardness after material removal, otherwise you will be in the transition area, which may meet the effective case depth requirement, but not the case hardness requirement of 90 HR15N minimum.

 

[Engparts]

What technique(s) can be used to control the near surface hardness depth to maintain sufficient hardness after material removal?

 

[mfgenggear]

""If case depth was .035 with hardness of 15N 91, then ground to remove .025 leaving case at .010, what could I expect the hardness to be?"

Your case depth will be below the case hardness requirement.

"How can the hardness of 15N 90 min be controlled for the full depth of case? "

Depending on the Material, & case depth specified, the surface case hardness can be maintained between .003-.010 deep.
Limit your stock removal to 20% of the effective case depth specified.

Have your facility or your supplier verify a test piece
for the conformance of case depth, case hardness at the depth
of stock removal (example case hardness 15N 90 min @ .005 depth. and also verify core hardness, metlab req'mts per the spec.