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Wrap-up

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Lesson 10·QC and failure

Failure modes — white-layer spall, network cracking, distortion, embrittlement

Five ways a nitrided tool fails in service, how to read each one from a microsection, and when 'the nitride failed' is honestly 'the wrong recipe was specified.'

11 min readLesson 10 of 12

Tying it together

When a tool fails after nitride, work this checklist

Before scrapping the part:

Get a microsection from the failure zone. Polish through 1 µm diamond, etch with 2-3% Nital, photograph at 100×, 500×, and 1000×. Photographs taken before the part goes to scrap are the only forensic record once it is gone.

Get a second microsection from an unfailed zone on the same part if one exists. The comparison tells you whether the failure was localized (geometric or contact-driven) or general (recipe or substrate).

Pull the certificate and check what was actually delivered. Compare the hardness traverse, compound-layer thickness, and case depth against the spec on the print. Most "the nitride failed" calls turn out to be "the nitride did not match what was specified."

Look at the fracture face under low-power optical first. Spall flakes, intergranular failure surfaces, and substrate fatigue striations look different even at 30×. Mineralogy and SEM come second, after you know what you are looking for.

Most "the nitride failed" calls are honestly "the wrong recipe was specified." Before blaming the vendor, check what the print actually asked for, and whether the substrate and corner geometry could have delivered the result regardless of who ran the cycle.

Up next: writing the spec.

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