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

Pre-hard stock arrives at the shop hardened and tempered by the mill to a fixed range, typically 40-44 HRC for hot-work grades and 28-32 HRC for mold grades. The builder rough machines and finish machines in the hardened condition, then ships the die. There is no heat-treat cycle, no quench distortion, no post-heat-treat grind. Total elapsed time is dominated by machining hours.

Through-hard stock arrives soft-annealed at roughly 22 HRC. The builder rough machines to within 0.020-0.060 inch of net on critical surfaces, stress relieves, semi-finishes, sends the part out for vacuum harden and double temper to the target hardness, and then finish machines and EDMs after heat treat. Stock allowances on critical surfaces are 0.005-0.015 inch per side to absorb quench distortion. The hardness ceiling depends on the grade and the temper. H13 at 50-52 HRC is the standard forge service window.

The two workflows are not interchangeable. Each has a hardness ceiling, a distortion profile, and a lead-time signature, and matching the workflow to the application is the engineering decision this lesson covers.