Step 1 of 8
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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.
Step 1 of 8Substrate and process
The vendor needs to know the grade because nitriding behavior depends on alloy chemistry: H13 has the Cr/Mo/V content to build a deep hardened case, 1018 does not. The vendor also needs the prior heat-treat condition because the tempering temperature defines the upper bound on the nitriding cycle. Run a cycle 20°C below temper and the core hardness survives; run above temper and the part softens. Specify grade, condition, and the temper temperature.
The process family decides the equipment, the cycle, and the achievable compound layer chemistry. Three callouts cover most tool and die work: gas nitriding per AMS 2759/10B for controlled gas cycles, plasma (ion) nitriding for low-distortion and stainless work, and ferritic nitrocarburizing per AMS 2759/12 when the compound layer needs to be ε-dominant on a non-alloy or low-alloy substrate. The standard reference does most of the heavy lifting if cited correctly; AMS 2759/10B includes Kn ranges, dissociation control, and certification requirements by class. Cite the standard and the class.
Substrate: AISI H13, hardened and tempered to 48-50 HRC, tempered at 595°C minimum.
Process: Gas nitriding per AMS 2759/10B, Class 2.
Quick check
A print specifies "Process: AMS 2759/10B" with no class called out. The vendor runs to Class 3 (the most permissive Kn range). Why does the missing class number open a hole in the spec, and what should the callout read?