Step 3 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 3 of 8Surface hardness
HRC alone on a nitrided surface is wrong. The Rockwell C indenter penetrates 150-200 µm into the case, deeper than most compound layers and a significant fraction of the diffusion zone, and the reading is a weighted average of case and substrate. Specify the scale, the load, the depth at which the measurement is taken, and the standard. HV 0.05 (50 gf Vickers) at 5-10 µm depth per ASTM E384 captures the compound layer; HV 0.5 (500 gf) at 100 µm depth captures the diffusion zone. The HRC-equivalent number is acceptable as a sanity check, not as the controlling measurement.
Surface hardness 60-65 HRC equivalent, measured as HV 0.05 = 900-1100 at 5-10 µm depth per ASTM E384.
Quick check
A certificate reports surface hardness 62 HRC on an 8 µm compound layer. The print called out 900-1100 HV 0.05. Does the HRC number satisfy the spec?