Intro
14%
Pre-nitride heat treatment — you can't nitride a soft die
Why the temper temperature has to sit above the nitride cycle by 30-50°C, why EDM without stress relief is the single most common cause of premature nitrided-tool failure, and what the print has to say before the part ships out for treatment.
A mold shop sends a P20 cavity insert out for nitriding. It comes back with a clean certificate: surface HV 950, compound layer 7 µm, case depth 0.25 mm per DIN 50190. The first production run pulls 4,000 shots before the cavity cracks in a network pattern across the parting line. The lab cross-sections the failed area and finds a 30 µm white recast layer under the nitride case, riddled with microcracks. The cavity was EDM-finished. It was not stress-relieved before shipping. The case did exactly what it was supposed to do. The substrate underneath never had a chance.
The lesson covers the work the print has to specify before the part leaves the shop floor.