Mold Steels: P20, 718H, NAK80, S136 and H13
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Mold quotes, especially from Asian toolmakers, list steels by trade names and standard numbers: P20, 718H, 2738, NAK80, S136, 2344. Many of them overlap. This is what they are and when each is the right call.
Pre-hardened steels
Pre-hardened steels arrive at working hardness, so the toolmaker machines them and they're ready. No heat treatment means no distortion and quicker changes.
- P20 (1.2311): the general purpose mold steel, around 28 to 34 HRC. Fine for many commodity resins like PP, PE and ABS at moderate volumes.
- 718H and 1.2738: P20 with added nickel, which keeps hardness consistent through large blocks. Around 33 to 38 HRC. Common for large molds, and it polishes better than plain P20.
- NAK80: a precipitation hardened steel supplied around 40 HRC with a very clean structure. It polishes to a mirror and takes texture evenly, so it is popular for cosmetic and clear parts.
Through-hardened steels
These are machined soft, then heat treated to full hardness. They last much longer and resist wear, at the cost of heat treatment time and some distortion to correct afterwards.
- H13 (1.2344, also sold as 2344 or 8407): hardened to roughly 48 to 52 HRC. Tough and wear resistant, and the usual choice for long runs and glass-filled or other abrasive resins.
- S136 and other 420 stainless grades (1.2083): hardened to about 48 to 52 HRC. Corrosion resistant, so they suit PVC and other corrosive resins, humid conditions and molds that must stay clean, like medical and optical parts. They polish very well.
- S136H: the pre-hardened version, around 30 to 35 HRC, for corrosion resistance without heat treatment.
Which steel for which job
| Job | Typical steel |
|---|---|
| Prototype or short run, commodity resin | P20, or aluminum |
| Medium volume, larger molds, decent polish | 718H or 1.2738 |
| Cosmetic, textured or clear parts | NAK80, or S136 at high volume |
| Glass-filled resins and long runs | H13 |
| PVC, corrosive resins, medical or optical | S136 or 420 stainless |
Many molds mix steels: a pre-hardened mold base with hardened cavity inserts, and hardened inserts at gates and other wear points.
Check the quote
Ask for the steel grade and brand for the cavity, core, slides and inserts separately, with the hardness and whether a mill certificate comes with it. P20 from an unnamed mill and branded 718H are not the same thing, and the difference shows up in polish and mold life. Mold life also depends on the mold class; see aluminum vs steel injection molds.
We specify steels in every tooling quote.