Step 4 of 4
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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.
Step 4 of 4Surface prep and masking
The part arrives clean, dry, and free of oil, cutting fluid, drawing compound, and shop dirt. Nitrogen will not diffuse through an organic film, and oil-contaminated areas come out as un-nitrided soft spots. Vendors run a degreasing step on arrival, but a heavily contaminated surface can defeat it. No plating, no prior coating, no residue from a previous PVD or CVD job; document any strip operation on the traveler. Sandblasting is optional; it depassivates stainless and some high-Cr grades, adds nothing on most tool steels, and is never a substitute for proper degreasing.
Areas that must remain machinable or threadable after nitriding need masking. Copper plating (25-50 µm electroplate) blocks nitrogen ingress for both gas and plasma. Copper-bearing paste is a lower-cost alternative for short cycles. Stop-off paints work for some salt-bath and gas processes but outgas in plasma chambers; plasma uses mechanical masks (stainless caps, threaded plugs) instead. Document the masking method on the print along with the masked surfaces.
Quick check
A part going to plasma nitride has six M10 threaded holes that must remain serviceable for assembly after the cycle. The shop's standard masking is anti-nitriding paint. What changes for plasma, and what is the alternative?