How to choose the right steel for injection molds: P20, H13, S7, 420SS, and more. Compare hardness, wear resistance, and cost.
Why Mold Steel Matters
The mold steel directly impacts tool life, part quality, cycle time, and maintenance frequency. Choosing the wrong steel can lead to premature wear, corrosion, or heat checking.
Common Mold Steels
P20 (1.2311) — Pre-hardened to 28-32 HRC. Good for general-purpose molds. Easy to machine. Low cost.
H13 (1.2344) — Hot-work tool steel. Hardness 44-52 HRC. Excellent for high-cavity-pressure molds and hot runner systems.
S7 — Shock-resistant tool steel. 54-58 HRC. Good for molds with thin cores or sharp edges that might chip.
420 Stainless (1.2083) — Corrosion-resistant. 48-52 HRC. Used for molds processing PVC, nylon with glass fiber, or medical applications.
NAK80 — Pre-hardened 37-43 HRC. Excellent polishability for optical-grade parts. No heat treatment needed after cutting.
Selection Criteria
Production Volume: Low volume (under 10k) → P20 or 7075 aluminum. Medium (10k-100k) → P20 or 1.2343. High (over 100k) → H13, S7, or D2.
Material Being Molded: Glass-filled nylons, PEEK, LCP → 420SS or H13. Standard ABS/PP/PE → P20 or NAK80. PVC → 420SS for corrosion resistance.
Surface Finish: Glossy/textured → NAK80 or 420SS (mirror polish possible). Standard → P20.
Surface Treatments
Nitriding adds surface hardness to 65-70 HRC. PVD/CVD coatings (TiN, TiAlN, DLC) reduce friction and improve release. Chrome plating restores dimensions on worn cavities.