P20 tool steel is one of the most widely used materials for pultrusion die and mandrel construction. Its combination of pre-hardened condition, good machinability, and polishability makes it a practical choice for a broad range of pultrusion tooling applications — particularly where lead time, machining complexity, and development flexibility are important factors. This article covers P20’s composition and mechanical properties, how it compares to H13, 718H, and other common tooling steels, and the conditions under which it is and is not the appropriate choice for pultrusion dies.
Key Takeaways
- P20 (DIN 1.2311) is a pre-hardened Cr-Mo-Ni tool steel supplied at 28–32 HRC, offering excellent machinability and good polishability.
- It is well suited to prototype, development, and moderate-production pultrusion tooling where lead time and die rework matter.
- H13 is preferred for high-volume, highly abrasive, or elevated-temperature pultrusion; 718H offers better polish uniformity for large or high-spec cavities.
- Surface treatments such as hard chrome plating and nitriding are standard for all pultrusion mold materials, including P20.
P20 Composition and Mechanical Properties
P20 (AISI P20, DIN 1.2311) is a low-carbon chromium-molybdenum-nickel tool steel supplied in the pre-hardened condition by most steel producers. Its typical chemical composition is as follows:
| Element | Typical Range (%) | Function |
|---|---|---|
| Carbon (C) | 0.28–0.40 | Hardness and strength base |
| Chromium (Cr) | 1.80–2.20 | Hardenability and wear resistance |
| Molybdenum (Mo) | 0.15–0.30 | Strength and toughness at temperature |
| Nickel (Ni) | 0.90–1.20 | Toughness and ductility |
| Manganese (Mn) | 0.60–1.00 | Hardenability |
| Silicon (Si) | 0.20–0.80 | Deoxidation and strengthening |
Key mechanical properties in the standard pre-hardened condition: hardness 28–32 HRC; tensile strength 965–1200 MPa depending on supplier and heat treatment batch; thermal conductivity approximately 34–41 W/m·K at room temperature. The pre-hardened supply condition is P20’s most practically significant characteristic for tooling applications — it arrives from the steel supplier at working hardness, eliminating the quench-and-temper cycle that harder tool steels require after machining.
Why P20 Is Used in Pultrusion Tooling
Pultrusion molds operate under continuous thermal cycling between ambient and working temperatures of 130–170°C, sustained contact with abrasive glass fiber reinforcements, and chemical exposure from resin systems and internal mold release agents. Within these operating conditions, P20 offers several practical advantages.
Machinability is the primary reason P20 is specified for complex tooling. At 28–32 HRC, it machines significantly faster than H13 at HRC 48–52, with lower tool wear and better surface finish from the cut. For pultrusion dies with complex cross-section geometry — thin internal ribs, asymmetric profiles, multiple mandrel passages — the machining time difference between P20 and a harder steel is substantial. P20 also allows modification and rework after initial machining without returning the tool to a heat treatment facility, which is important during profile development when die adjustments are likely.
Polishability is the second practical advantage. P20 achieves cavity surface finishes of Ra 0.4 μm or better with standard polishing procedures, which is the surface roughness specification required for pultrusion mold cavities to achieve acceptable profile surface quality and manageable pulling force. 718H — a modified P20 variant with higher nickel content — achieves marginally better polish consistency, but standard P20 meets the specification for the majority of glass fiber composite profiles.
Lead time is the third factor. Because no post-machining heat treatment is required, P20 molds move directly from finish machining to surface treatment and delivery. For H13 molds, the heat treatment cycle adds 1–3 weeks to the manufacturing timeline depending on the furnace schedule and component size.
Comparison with Alternative Tooling Steels
| Material | Typical Hardness | Machinability | Polishability | Best Application |
|---|---|---|---|---|
| P20 | 28–32 HRC | Excellent | Very good | Prototype, development, and moderate production run pultrusion tooling |
| 718H | 33–38 HRC | Good | Excellent | Higher polish requirement or longer service life than standard P20 |
| H13 (2344) | 46–52 HRC after heat treatment | Moderate | Good | High-volume production, elevated temperature, carbon fiber or abrasive resin systems |
| D3 / Cr12 | 58–64 HRC | Poor | Poor to moderate | Maximum wear resistance; not typically used for pultrusion cavity surfaces |
| 40Cr | 18–25 HRC typical | Excellent | Good | Low-cost tooling for short runs or low-abrasion profiles |
718H is a modified P20 with higher nickel content (approximately 0.85–1.20% Ni) and tighter compositional control, supplied pre-hardened to 33–38 HRC. It offers better hardness uniformity through large cross-sections than standard P20 — relevant for wide or thick mold bodies where P20 can show hardness gradients from surface to core — and slightly better polish consistency. For pultrusion tooling where standard P20 meets surface finish requirements, 718H adds cost without proportional benefit. For tooling requiring high polish uniformity across large surfaces, or where service life needs to exceed what P20 delivers, 718H is the logical upgrade.
H13 (European designation 2344) is the correct choice when operating conditions exceed P20’s capability: high-volume production runs where cavity wear accumulates rapidly, resin systems with highly abrasive fillers, carbon fiber reinforcements, or operating temperatures above 160°C where P20’s lower hardness results in accelerated cavity wear. H13 requires heat treatment after rough machining and before finish machining, adding lead time and manufacturing complexity. Its higher hardness makes it more difficult to modify after final machining, which is a disadvantage during die development.
P20 vs H13 — Side-by-Side
| Attribute | P20 | H13 |
|---|---|---|
| Supply hardness | 28–32 HRC (pre-hardened) | Soft annealed for machining; hardened to 46–52 HRC |
| Machinability | Excellent | Moderate |
| Post-machining heat treatment | Not required | Required |
| Typical lead time | Shorter | 1–3 weeks longer |
| Die modification after machining | Relatively easy | Difficult; may require re-heat-treatment |
| Wear resistance | Moderate | High |
| Best for | Prototypes, development, moderate runs | High-volume, abrasive, carbon fiber, >160 °C operation |
Cost and Availability
P20 is generally lower in material cost and faster to procure than H13 or 718H for equivalent mold sizes, mainly because it is supplied pre-hardened and requires no post-machining heat treatment. Tooling lead time is typically 1–3 weeks shorter than H13, a significant factor during profile development. For small-to-medium pultrusion dies where surface finish and wear requirements are moderate, P20 often delivers the lowest total tooling cost. For very large or high-cavity-count molds, the cost difference narrows because material cost becomes a smaller fraction of total machining and surface-treatment expense.
Surface Treatment for Pultrusion Molds
Regardless of base material, pultrusion mold cavities require surface treatment after finish machining to improve wear resistance and reduce pulling force. The two standard treatments are hard chrome plating and nitriding.
Hard chrome plating (0.02–0.05 mm thickness) deposits a hard, low-friction surface that reduces fiber abrasion of the cavity walls and improves resin release. It is applicable to P20, 718H, and H13 equally. Chrome plating adds a small but measurable dimensional change — typically 0.01–0.025 mm per surface — that must be accounted for in the finish machining dimensions.
Nitriding produces a hard case (typically 0.1–0.3 mm depth at 65–70 HRC surface hardness) by nitrogen diffusion without significant dimensional change, preserving the tight tolerances achieved in finish machining. It is particularly well suited to P20 and 718H molds where dimensional stability through the treatment process is critical. Nitrided P20 achieves surface hardness that significantly exceeds its bulk hardness, giving cavity wear resistance closer to H13 while retaining the machinability advantage of the softer base material.
PVD coatings (TiN, TiAlN) are used in specific applications where maximum surface hardness and chemical resistance are required, but are less common in standard pultrusion tooling than chrome plating or nitriding.
When to Specify P20 — and When Not To
P20 is the appropriate choice for pultrusion tooling when the project involves complex profile geometry requiring extensive machining, prototype or development tooling where die modification is likely, moderate production volumes where cavity wear at 28–32 HRC is acceptable, and timelines that cannot accommodate post-machining heat treatment. It is also the standard choice for mandrels in tubular profile production, where the mandrel geometry is complex and the thermal and abrasive loads are lower than on the outer die cavity.
P20 is not the appropriate choice for very high production volume runs where cavity wear will require premature die replacement, for carbon fiber pultrusion where fiber abrasivity is significantly higher than glass, for resin systems containing highly abrasive fillers such as silica or calcium carbonate at high loading, or for profiles requiring very high surface quality where 718H’s superior polish consistency justifies the additional cost.
Need Pultrusion Mold Material Guidance?
Choosing between P20, 718H, and H13 depends on production volume, profile geometry, abrasive load, and lead-time constraints. Talk to our tooling team about material selection and pultrusion machine compatibility.
For profile tooling applications, see our handrail pultrusion dies.
Frequently Asked Questions
What is the hardness of P20 tool steel for pultrusion molds?
Standard P20 is supplied pre-hardened to 28–32 HRC. This is lower than H13 at HRC 46–52 after heat treatment, which means P20 has lower abrasion resistance but significantly better machinability. The pre-hardened supply condition eliminates the post-machining quench-and-temper cycle required for harder steels, reducing lead time and the risk of distortion during heat treatment.
What is the difference between P20 and 718H for pultrusion tooling?
718H is a modified version of P20 with higher nickel content and tighter compositional control, supplied pre-hardened to 33–38 HRC — slightly harder than standard P20. Its primary advantage over P20 is better hardness uniformity through large cross-sections and superior polish consistency, which matters for wide or thick mold bodies and for applications requiring the highest achievable cavity surface finish. For most standard glass fiber pultrusion profiles, P20 meets the Ra 0.4 μm surface roughness specification and 718H adds cost without proportional benefit.
When should H13 be used instead of P20 for pultrusion molds?
H13 is the appropriate choice when cavity wear at P20 hardness is not acceptable — typically in high-volume production where cavity wear accumulates rapidly, carbon fiber pultrusion where abrasivity is significantly higher than glass fiber, resin systems with abrasive fillers, or operating temperatures above 160°C where P20’s hardness degrades faster than H13’s. H13 requires post-machining heat treatment, adding 1–3 weeks to manufacturing lead time and limiting the ability to modify the die after final machining.
Does P20 pultrusion tooling require surface treatment?
Yes. All pultrusion mold cavities require surface treatment after finish machining regardless of base material. Hard chrome plating (0.02–0.05 mm) and nitriding are the two standard treatments. Nitriding is particularly well suited to P20 because it produces a hard case at 65–70 HRC surface hardness without dimensional change, giving the cavity wear resistance significantly above the base material hardness while preserving the tight machining tolerances. Chrome plating adds a small dimensional change that must be compensated in finish machining dimensions.
Can P20 pultrusion molds be modified after machining?
Yes, and this is one of P20’s practical advantages over harder steels. Because P20 is pre-hardened and does not require a subsequent heat treatment cycle, modifications — cavity dimension adjustments, port repositioning, additional venting — can be made by re-machining without returning the tool to a heat treatment facility. This flexibility is particularly valuable during profile development, where die adjustments based on first-article trial results are common. H13 molds, by contrast, are difficult to modify after final hardening without risking dimensional distortion.
What surface roughness is required for pultrusion mold cavities?
Cavity surface roughness must achieve Ra 0.4 μm or better after final polishing. This specification is necessary to minimize pulling force, ensure consistent resin release from the cavity walls, and achieve acceptable surface finish on the pultruded profile. P20 reaches this specification with standard polishing procedures. Higher surface roughness increases pulling force, promotes resin build-up on cavity walls, and produces surface defects on the profile that may require secondary finishing operations.
