Writing the spec — what goes on the print

A controlled nitriding job produces evidence, not assertions. The certificate that ships with the parts should include the microhardness traverse (at least ten data points from the surface down through the core, with the depth, load, and standard noted), not just a single surface number. A photomicrograph of the compound layer at 500× or higher magnification, with the etchant identified (Nital 2-3% is standard, alternative reagents identified if used), showing the compound layer thickness measured in microns and the phase identified. Effective case depth, with the measurement method and the definition (DIN 50190-3 NHD, AMS 2759/10 effective, ISO 18203). Witness coupon results if a coupon was specified, on the same substrate run in the same cycle, sectioned and measured. Dissociation log or Kn log if AMS 2759/10B was cited. Any certificate that arrives with only a surface hardness number and a case depth value is missing the evidence the spec asked for.