Step 5 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 5 of 8Compound layer thickness and phase
Compound layer thickness has a sweet spot. Under 5 µm the layer wears off quickly. Between 5 and 15 µm it serves its job. Above 15-20 µm it spalls under flexure or impact. Specify the range. Phase matters for the application: γ' (Fe₄N) for impact, ε (Fe₂₋₃N) for sliding wear and corrosion. A mixed ε/γ' layer with a sharp phase boundary is the worst of both worlds and cracks along the interface. Specify the phase and require verification by microsection examination on a witness coupon.
Compound layer 4-8 µm, γ'-dominant per microsection examination.
Quick check
A stamping die for galvanized stock needs a compound layer optimized for galling resistance. Write the spec line covering thickness, phase, porous zone, and verification method.