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

Typical substrate: H13, premium H11 grades (Bohler W302, Uddeholm Dievar), Nitralloy 135M for premium work. Service environment: 1100-1200°C billet contact, mechanical impact, thermal cycling between hits.

Target case depth: 0.4-0.8 mm. The diffusion zone has to be deep because Hertzian contact stress from the forging penetrates well past any plausible compound-layer thickness, and the load needs a graded hardness profile that does not bottom out into the unhardened core. Target compound layer: thin, 5-10 µm, γ'-dominant. The dominant failure mode is heat-checking that initiates at the compound layer / diffusion zone boundary when the compound layer is thick or contains an ε/γ' phase boundary, then propagates into the diffusion zone under thermal cycling.

Preferred process: 2-stage Floe gas cycle, or plasma. The Floe cycle (Lesson 3) is the standard call. Stage one builds the compound layer to a controlled thickness at moderate Kn. Stage two drops Kn and drives the diffusion zone deep without further compound-layer growth. Total cycle time 60-80 hours. Plasma is the call when distortion control matters more than throughput. Distortion budget on a typical forge insert is 0.0005-0.001 inch per inch.