The mold steel used for MIM injection tools directly affects mold life, part surface finish, and maintenance frequency. Three grades dominate: H13, S136, and NAK80 — each with distinct characteristics.
MIM mold steel comparison:| Grade | Type | Hardness (HRC) | Corrosion Resistance | Polishability | Wear Life (shots) | Relative Cost | Best For |
|---|---|---|---|---|---|---|---|
| H13 | Hot work tool steel | 48-52 (pre-hardened) | Low | Good | 500k-2M | 1.0x (baseline) | High-volume production, long-running programs |
| S136 (1.2083) | Stainless mold steel | 48-52 (pre-hardened) | High | Excellent | 300k-1M | 1.3-1.5x | Corrosive binders (POM catalytic), medical/optical parts |
| NAK80 | Pre-hardened steel | 37-43 (as-delivered) | Moderate | Excellent (mirror finish) | 200k-500k | 1.4-1.6x | Cosmetic surfaces, textured finishes, low-medium volume |
- H13: Default choice for most MIM programs. Good wear resistance, proven track record, and lowest cost. Suitable for standard 316L, 17-4PH, and Fe-2Ni materials
- S136: Essential when using POM-based binders with catalytic debossing — the nitric acid catalyst attacks unprotected steel. Also preferred for parts requiring high surface finish or optical-grade surfaces
- NAK80: Pre-hardened and delivered ready for cavity machining (no heat treatment needed). Excellent for textured surfaces and cosmetic parts. Trades off some wear life for superior polishability and faster mold fabrication
H13 tool steel offers the longest wear life (500k-2M+ shots) for standard materials. For corrosive POM/catalytic debinding environments, S136 stainless mold steel is required despite its somewhat lower wear life.
Mold steel selection should be part of the DFM discussion — not an afterthought when the tooling RFQ is already out.