AISI P20 Pre-Hardened Mold Steel: Plastic Injection Molding Standard
ASTM A681 (modified) · Updated: 2026-05-25
AISI P20 is a chromium-molybdenum pre-hardened mold steel supplied at 28-32 HRC—ready for machining directly into plastic injection molds without requiring post-machining heat treatment. Nominal composition: 0.28-0.40% C, 1.4-2.0% Cr, 0.3-0.55% Mo, and optionally 0.85-1.25% Ni for improved polishability and through-hardness in large blocks. The pre-hardened condition eliminates the dimensional changes, distortion, and surface scaling associated with post-machining heat treatment. P20+Ni (modified with nickel) is the standard for large automotive injection molds (bumpers, dashboards) requiring uniform hardness throughout thick sections. Polishable to SPI A-2 finish; texturing by chemical etching for grain effects.
Quick Facts
| Category | Tool Steel |
| Standard | ASTM A681 (modified) |
| Density | 7.85 g/cm³ |
| Yield Strength | 850 MPa (123 ksi) at 28-32 HRC |
| Tensile Strength | 1,000 MPa (145 ksi) at 28-32 HRC |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN 40CrMnNiMo8-6-4 | Compare |
| DIN 1.2738 | Compare |
| NAK80 | Compare |
| 3Cr2Mo | Compare |
| P20+Ni | Compare |
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Frequently Asked Questions
How does P20 compare to H13 for injection molds?
P20 is pre-hardened and machined directly into the mold—lower cost, simpler process. H13 is a through-hardening hot work steel requiring heat treatment after rough machining, then finish machining/grinding. For plastic injection molds running below 200°C, P20 is standard. For molds running above 250°C (engineering plastics, thermosets) or requiring exceptional polish (optical lenses), H13 or stainless mold steels (420, NAK80) are preferred.