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

P20 ships pre-hardened to 28-32 HRC and is sold widely as a general-purpose tool steel. It is a mold steel, optimized for plastic injection and low-stress applications. The 28-32 HRC core is well below the 44 HRC floor for hot-forge contact stress, and the steel chemistry was never designed to retain hardness at die-surface temperatures of 400-600°C. P20 belongs in the mold shop. Using it for a hot-forge cavity, even one rated as low-stress, is a substrate selection error that no surface treatment can repair. Aluminum-bronze inserts, die holders, and forging fixtures that do not see direct contact stress are legitimate P20 applications. The cavity itself is not.

The trap is that P20 ships pre-hard at a competitive price, machines well, and the catalog category often reads "general-purpose tool steel." A buyer or scheduler who has not internalized the hot-work versus mold-work split picks P20 because it is on the shelf and pre-hard, and the die washes out within a few thousand hits. The fix is engineering review on any forge cavity quoted in P20, regardless of how the supplier categorizes the grade.