Transfer of ausforming parameters to scaled forging tools

Abstract

Forging tools are exposed to cyclically changing thermo-mechanical stress conditions leading to its failure. Damage phenomena on the tool engraving cannot be entirely avoided by hardening the surface, as this leads to a more brittle behaviour and thus to lower ductility of the material, which can intensify the occurring damage effects. The forming of steel below the recrystallisation temperature in the metastable austenite area, known as ausforming, offers the possibility to increase strength and hardness without affecting ductile properties, due to simultaneous grain refinement. In this study, ausforming was used to produce forging dies with increased wear resistance from tool steel X37CrMoV5-1 (AISI H11) by achieving higher hardness in the surface area while maintaining a ductile base material. Suitable forming and tempering parameters were derived from previous studies in which ausformed cups from tool steel X37CrMoV5-1 (AISI H11) with a downscaled geometry have been investigated in mechanical pulsation tests. To achieve comparable properties, a process route with adapted surface-cooling conditions, a global true plastic strain of φ = 0.25 and a tempering temperature of 300 °C were applied. Further, the ausformed dies were compared with conventionally forged dies. The metallographic analysis and hardness measurements show that an increased hardness in the surface area can also be obtained for the actual formed dies. In order to see the influence of the thermomechanical alternating load on the die engraving under forging conditions, the performance of the ausformed tool will be investigated in service-life-time tests and compared to warm-formed and machined reference tools.