Pre-hard vs through-hard: which workflow, when

The trap is using pre-hard for an application that needs the hardness ceiling of through-hard. Hot-trim dies cutting forged steel at billet temperatures of 1000-1100°C see scale-loaded abrasive wear that grinds 42 HRC edges flat in 15-25K cycles. The same edges at 50 HRC last 60-100K cycles. Hot forge cavities for high-stress parts plastically deform at 42 HRC under repeated contact stress that 50 HRC tolerates. Any forge die in steel service where the failure mode is wear or plastic deformation is a poor candidate for pre-hard stock.

Pre-hard is the right call when the part is geometrically complex enough that post-heat-treat distortion would consume the cavity tolerance, when the application is low-stress (warm forging, low-volume prototype, die holders and shoes), or when the hardness gap genuinely does not matter because the dominant failure mode is something other than wear or deformation. A short-run trim die for soft aluminum forging is a fair pre-hard candidate. A production steel hot-forge cavity is not.