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

Typical substrate: H13, premium variants (Bohler W360 Isobloc, premium H13 ESR). Service environment: 450-500°C aluminum flow at extrusion pressures of 50-100 MPa across the bearing surface, abrasive wear from oxide in the billet, sticking of aluminum to the die surface.

Target case depth: 0.20-0.50 mm. The case carries the bearing pressure and the abrasive contact. Target compound layer: thin, 4-8 µm, predominantly γ' or controlled ε. The dominant failure mode is sticking and welding of aluminum to the bearing surface, which scores subsequent extrusions and tears the die. Aluminum welds easily to exposed iron and to porous ε compound layers. It does not weld easily to a dense thin γ' layer or to a properly oxidized post-FNC surface.

Preferred process: Floe gas cycle followed by a light bearing-surface polish that takes the compound layer down to 4-6 µm without removing it entirely; or salt-bath FNC with post-oxidation for high-volume commodity work. The polishing step is the trap. If the polish exposes substrate, the next extrusion sticks within meters of running and the die comes out for re-nitride. Multiple re-nitride cycles embrittle the diffusion zone, which is the failure documented in the Engineering Failure Analysis study on gas-nitrided H13 extrusion mandrels.