Category: Mold Manufacturing Reading time: 9 min Meta description: A detailed comparison of mold steel grades — P20/2311, H13/2344, NAK80, S136/2083, and D2/SKD11. Choose the right steel for your mold and avoid costly failures. URL: /blog/mold-steel-selection-guide/ Tags: mold-steel, tool-steel, P20, H13, NAK80, mold-making, grade-comparison
Choosing the wrong steel for a mold is an expensive mistake. If the steel is too soft, the mold wears out early. Too hard, and it becomes difficult to machine. Wrong grade for the application, and corrosion or thermal fatigue destroys the cavity.
This guide compares the most common mold steel grades — what they're for, what they cost, and how to choose.
Most mold steels fall into three categories:
| Category | Hardness Range | Key Property | Application |
|---|---|---|---|
| Pre-hardened | HRC 28-38 | Machinable without heat treatment | Mold bases, simple cavities |
| Through-hardening | HRC 45-58 | Wear resistance, heat treated after machining | Production cavities, slides |
| Corrosion-resistant | HRC 30-55 | Rust and chemical resistance | Medical, food contact, PVC |
| Property | Value |
|---|---|
| Supplied hardness | Pre-hardened to HRC 30-35 |
| Polishability | Good (up to SPI-A2) |
| Wear resistance | Moderate |
| Weldability | Good |
| Machinability | Excellent |
| Relative cost | $ (low) |
| Available in | Blocks up to 800×1200mm |
Best for: All-purpose cavity and core plates for mold bases, prototype molds, short to medium production runs.
Limitations: Not suitable for high-wear applications. Will show erosion after 500,000+ cycles with glass-filled materials.
Common uses: Mold bases, simple cavities for commodity plastics (ABS, PP, PE), prototype tooling.
| Property | Value |
|---|---|
| Heat treated hardness | HRC 45-52 |
| High temperature strength | Excellent (retains hardness to 540°C) |
| Polishability | Good |
| Wear resistance | Good-to-excellent |
| Machinability (annealed) | Good |
| Relative cost | $$ (moderate) |
Best for: Slides, cores, hot work applications, die casting dies, high-cavity-pressure applications.
Limitations: Not supplied pre-hardened — requires heat treatment after rough machining. Can distort during heat treatment.
Common uses: Injection mold slides and cores, aluminum die casting dies, extrusion dies, hot-runner manifolds.
| Property | Value |
|---|---|
| Supplied hardness | Pre-hardened to HRC 37-43 |
| Polishability | Excellent (mirror finish possible) |
| Wear resistance | Good |
| Machinability | Good |
| Relative cost | $$$ (high) |
Best for: Mirror-finished cavities, clear plastic parts, lens molds, cosmetic surfaces.
Limitations: Not for high-temperature applications or severe wear conditions.
Key advantage: NAK80 is a precipitation-hardening steel that achieves its hardness through an aging treatment rather than conventional quench and temper. This means it has exceptional dimensional stability — no distortion during machining.
Common uses: Optical lens molds, cosmetic part cavities, automotive lighting, clear medical components.
| Property | Value |
|---|---|
| Heat treated hardness | HRC 48-55 |
| Corrosion resistance | Excellent |
| Polishability | Excellent (mirror finish possible) |
| Wear resistance | Good |
| Machinability (annealed) | Moderate |
| Relative cost | $$$ (high) |
Best for: Corrosive plastics (PVC, POM, flame-retardant grades), medical parts, food-grade packaging.
Limitations: Higher cost, moderate machinability. Requires protection from carbon buildup during heat treatment.
Common uses: Medical device molds, food packaging molds, PVC pipe fittings, battery component molds.
| Property | Value |
|---|---|
| Heat treated hardness | HRC 58-62 |
| Wear resistance | Excellent |
| Toughness | Good |
| Machinability (annealed) | Moderate |
| Relative cost | $$$ (moderate-high) |
Best for: Stamping dies, trimming tools, wear plates, cooling channel inserts.
Limitations: Not for high-temperature applications. Brittle if not properly heat treated.
Common uses: Progressive stamping dies, blanking dies, slitter knives, cold forming tools.
| If your mold needs... | Choose... | Why |
|---|---|---|
| General purpose, low cost | P20 (2311) | Pre-hardened, cheap, machinable |
| High production volume (1M+) | H13 or 2344 | Heat-treatable, wear resistant |
| Mirror finish surface | NAK80 or S136 | Superior polishability |
| Corrosive plastic (PVC, POM) | S136 (420SS) | Corrosion resistance |
| Very high wear (glass-filled) | D2 (SKD11) or H13+coating | Extreme hardness |
| Die casting (aluminum) | H13 (2344) | Hot work resistance |
| Prototype/low volume | P20 (2311) | Fast to machine, low cost |
| Slides and moving parts | H13 (2344) | Abrasion resistance |
| Grade | Material Cost (per kg) | Total Mold Cost Impact |
|---|---|---|
| P20 / 2311 | $5-8/kg | Baseline (1x) |
| H13 / 2344 | $8-15/kg | 1.2-1.5x |
| NAK80 | $15-25/kg | 1.5-2x |
| S136 / 2083 | $15-20/kg | 1.5-2x |
| D2 / SKD11 | $8-15/kg | 1.2-1.5x |
Important: Material cost is only 5-15% of the total mold cost. Choosing a more expensive, better-suited steel is almost always the right decision if it extends mold life or enables better part quality.
Mistake 1: Using P20 for high-wear applications Result: Cavity wears out after 200,000 cycles. Mold needs repair or reworking. Cost: $3,000-10,000 in downtime and repair.
Mistake 2: Using H13 without proper heat treatment Result: Inconsistent hardness, distortion, reduced mold life.
Mistake 3: Using NAK80 for hot runner applications Result: Loss of hardness at elevated temperatures.
Mistake 4: Using S136 for general applications Result: Paying 2-3x more than P20 for benefits you don't need.
Coatings extend mold steel life significantly:
| Coating | Temperature Limit | Wear Improvement | Application |
|---|---|---|---|
| TiN (titanium nitride) | 600°C | 2-3x | General wear protection |
| TiAlN | 900°C | 3-5x | High-temperature molds |
| CrN (chromium nitride) | 700°C | 3-4x | Corrosion + wear |
| DLC (diamond-like carbon) | 350°C | 5-10x | Non-stick, smooth release |
| Nitriding | 500°C | 2-3x | Standard case hardening |
If your budget is tight and production is moderate: P20 (2311) is perfectly adequate. It handles 500,000+ cycles for standard materials.
If you need production reliability and mold life: Invest in H13 (2344) for moving components and high-wear areas. Use P20 for the mold base to control costs.
If appearance matters: NAK80 for mirror finishes, S136 for corrosion resistance. Both are the right investment when surface quality is non-negotiable.
If you're still unsure: Submit your requirements to app.moldkey.com/quote and our mold engineers will recommend the right steel for your application.