Application playbook — forge dies, stamping, plastic molds, gears, extrusion

Typical substrate: P20 pre-hard, 420 stainless for corrosive-resin work, premium grades (Stavax ESR, Mirrax, M310) for optical and clear cavities. Service environment: low temperature, polished surface required, dimensional precision in tenths, sometimes acidic gases from PVC or flame-retardant resins.

Target case depth: 0.15-0.30 mm. Shallow, because the mold sees low contact stress and the dominant concern is dimensional stability, not load-bearing case. Target compound layer: very thin, 3-5 µm, or compound-layer-free if the cavity will be PVD-coated. The compound layer is a liability on most mold work: it adds dimensional growth on a tight cavity, it can crack and transfer marks onto the molded part, and it interferes with PVD adhesion.

Preferred process: plasma, almost always. Plasma runs at 480-510°C, well below P20's 595°C temper. The atmosphere lever is set lean (low N₂ in the N₂/H₂ mix) to grow little or no compound layer. Distortion budget is the tightest of any nitriding application: 0.0002-0.0005 inch per inch on a precision cavity. Dominant failure modes: dimensional growth that puts the cavity out of tolerance, and corrosion in storage when the resin chemistry is aggressive. QPQ on 420 cavities running PVC defends against the second.