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

Typical substrate: D2, A2, M2, premium powder-metallurgy grades (Vanadis 4 Extra, Vanadis 8, CPM-10V, CPM-15V). Service environment: high contact stress against sheet stock, galling and adhesive pickup from galvanized or coated stock, abrasive wear from sheet-edge slivers.

Target case depth: 0.20-0.40 mm. Shallower than a forge die because cold-work contact stress does not penetrate as deep. Target compound layer: thicker, 15-25 µm, ε-dominant. The thick ε layer does the real wear work; it resists galling against zinc and aluminum coatings far better than a thin γ' layer. The dominant failure mode is adhesive pickup that scores the die surface, which is almost always a sign that the compound layer is the wrong phase, too thin, or has been ground off in finishing.

Preferred process: gas FNC (Lesson 6) or salt-bath FNC (Lesson 4). Salt-bath FNC delivers a dense ε-dominant compound layer in a 90-minute cycle, which dominates high-volume work. Gas FNC under Kn and Kc control delivers the same phase chemistry with a tighter thickness band and better distortion budget. QPQ is the right call when corrosion resistance against humid storage matters; the post-oxidation step seals the porous outer zone.