Vendor selection and QC sign-off — separating real nitriding houses from job shops

The last eleven lessons covered what to spec. This one covers who to send it to.

A nitriding vendor lives in one of three tiers. Tier one is a Nadcap- or CQI-9-audited shop running closed-loop atmosphere control to AMS 2759/10 or /12, with on-site metallography and full traceability per load. Tier two is a competent commercial shop running Kn-controlled or potential-controlled equipment without the formal audit overhead, with microhardness on-site and the willingness to run a witness coupon. Tier three is a job shop with one retort, an ammonia bleed, a Rockwell tester, and a furnace log written on a clipboard. All three call what they do "nitriding." The 30-minute phone call sorts them.