Study of Duplex Plasma Treatment Applied to AISI H13 Steel: Surface Properties and Forging Die Performance

AISI H13 tool steel is commonly used in hot forging applications, where service life is predominantly limited by surface-related failures such as abrasive wear and plastic deformation. Duplex treatment – a surface engineering process that combines nitriding with a thin, hard coating deposited using Physical Vapor Deposition (PVD) technology – has demonstrated significant improvements in surface hardness and wear resistance, yet a systematic understanding of how surface integrity changes throughout the entire multi-stage manufacturing sequence remains lacking. This study addresses this gap by characterizing surface properties across sequential processing stages applied to quenched and tempered AISI H13: high-speed milling, mechanical polishing, low-pressure gas nitriding, intermediate microblasting, low-pressure plasma nitriding and PVD coating (CrAlTi-based), and final microblasting. At each stage, surface integrity was assessed through roughness, topography, morphology, microhardness, coating adhesion, and wettability. Also, die performance was evaluated by hot forging laboratory-scale tests. Results reveal that each treatment step imparts distinct modifications. Low-pressure gas nitriding increased subsurface hardness without a compound layer. Intermediate microblasting increased roughness and promoted mechanical interlock for coating deposition. Low-pressure plasma nitriding and PVD coating introduced droplets and porosity, increasing hardness and roughness. Final microblasting reduced the presence of droplets and peak heights. Satisfactory coating adhesion was found. Wettability measurements showed a hydrophobic final surface. After hot forging cycles, as-milled dies exhibited more aggressive wear and plastic deformation than duplex-treated dies. Failures on the latter were attributed to substrate hardness loss. The findings provide a framework for optimizing duplex treatment parameters to enhance service performance of AISI H13 dies.