CoatingIQ
← Course index

Wrap-up

91%

Lesson 11·Specification

Writing the spec — what goes on the print

An annotated nitriding callout template a competent vendor can hit and an incompetent one will refuse, with the eight elements that turn a wish into a spec.

7 min readLesson 11 of 12

Tying it together

Common spec mistakes that doom the job

Calling out HRC alone with no scale and no load. The Rockwell C reading on a thin case is meaningless; the vendor can deliver an HRC number that translates to a case that fails in service.

"Case depth 0.020 inch" with no definition. Total NHD and effective case depth can differ by 2× on the same part. The vendor picks the favorable definition.

"Minimize white layer" without a number. A vendor running a high-Kn cycle will produce 15 µm of compound layer and document that they "minimized" relative to what they could have grown.

Quoting AMS 2759/10 without specifying class. The standard has classes with different Kn ranges, different case depth requirements, and different certification levels. AMS 2759/10B Class 1, Class 2, and Class 3 are different specifications.

No substrate condition on the print. The vendor either asks (delay) or guesses (failure). H13 at 50 HRC and H13 in the annealed state nitride differently, and the vendor cannot tell from looking at the part.

Up next: vendor selection.

Sources