Life time enhancement of forging dies with tailored diffusion treatments

Hot forging processes play an important role in the production of safety relevant parts with excellent mechanical properties. Their economic efficiency depends on the service life time, which is limited by the occurring wear. Modifying the surface zone layer with diffusion treatments such as nitriding can minimize the wear progress and provide material resistance against thermal softening. This reduces plastic deformation and abrasive wear. However, intensely nitrided surfaces often show increased crack sensitivity and therefore chipping of material. Thus, the combination of different diffusion treatments and to some extent following thermal post-treatments (TPT) still in the vacuum as well as new approaches using localized treatments by applying different coverage techniques to prevent the nitrogen diffusion in certain areas are part of this study. Localized diffusion treatments offer the possibility to structure the surface with differently designed patterns and generate surfaces with ductile zones between nitrided ones. Thus, a positive influence on the resistance against the formation and propagation of cracks under thermal shock conditions is accomplished. The evidence of the achieved advantages is provided through a system of different testing methods, which enable the abstraction of the thermal shock conditions in different stages. This spans from a custom-designed testing unit with a heated stamp and adjustable quenching conditions up to serial forging tests. Special analytical methods are applied to characterize the crack sensitivity of the modified surface zone layers.