Case depth in carburizing or nitriding

A. Here are some American standards of possible relevance. Links to ISO, British and MIL-S-12515C SURFACE HARDENING: FLAME AND INDUCTION (FOR FERROUS ALLOYS) [inactive]

MIL-STD-1878A CARBURIZING, GASEOUS ATMOSPHERE, PROCESS FOR [Canceled]
SAE-AMS2759/7 CARBURIZING AND HEAT TREATMENT OF CARBURIZING GRADE STEEL PARTS
ASTM A534 Standard Specification for Carburizing Steels for Anti-Friction Bearings
ASTM A255 Standard Test Method for Determining Hardenability of Steel
ASTM E1077 [withdrawn] Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens
ASTM G79 [withdrawn] Standard Practice for Evaluation of Metals Exposed to Carburization Environments
ASTM A37 Recommended Practice for Carburizing and Heat-Treatment of Carburized Objects -withdrawn 1936
ASTM A355 Standard Specification for Steel Bars, Alloys, for Nitriding

Search ISO specifications at http://www.iso.ch/iso/en/ISOOnline.frontpage
British Standards (BS) at http://bsonline.techindex.co.uk
British DEF, DTD, NES standards at http://www.dstan.mod.uk/ and DIN standards at http://www2.din.de/?lang=en

I am not sure exactly what you are seeking. Case [depth] is typically considered as the portion of a ferrous alloy, extending inward from the surface, in which the hardness is greater than that of the core.*   However, it is common to specify a minimum hardness at a given depth, and this can be achieved by various combinations of temperature, time, surface carbon activity, and initial alloy composition. Carburizing and nitriding occur by non-steady-state diffusion described by Fick's second law, with a concentration curve that decays from the surface into the bulk [Mathematical solution requires diffusion coefficients and the erf function, and is covered in metallurgy/ materials science courses]. To avoid extreme brittleness, an upper limit is sometimes placed upon the surface hardness.

*ASM Handbook, Volume 5, Surface Engineering, p. 948 (1994).

A. Tomer,
According to
https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=37183
there was no replacement named at the time the standard was cancelled. Though Ken Vlach's reply above suggests some alternatives.