What are the specific differences between P20 and 718H?
2026-06-02 09:20:40
P20 and 718H are the two most commonly used pre‑hardened mold steels in the plastic mold industry. Simply put, 718H is an “upgraded” or “improved” version of P20. The core parameter comparison table below will help you understand their differences intuitively, followed by a detailed breakdown of how these differences affect actual production.
I. Quick Comparison Table
| Dimension | P20 (1.2311) | 718H (1.2738) | Key Difference |
|---|---|---|---|
| Chemical composition | Cr‑Mo alloy steel | Cr‑Ni‑Mo alloy steel | 718H contains nickel (Ni) |
| Delivery hardness | HRC 28‑32 | HRC 33‑38 | 718H is harder, more wear‑resistant |
| Steel cleanliness | Standard | High (vacuum melting) | 718H has fewer impurities, better polishability |
| Mold life | approx. 100k‑300k shots | approx. 300k‑500k shots | 718H lasts longer |
| Polishability | Good (normal appearance) | Excellent (near mirror) | 718H suitable for high‑gloss/transparent parts |
| Cost | Lower (cost‑effective) | Higher (~15‑20% more expensive) | P20 saves money |
II. Deep Dive: Four Key Differences
1. Composition and Hardness (the most fundamental difference)
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P20: Chromium‑molybdenum (Cr‑Mo) steel. Delivery hardness usually HRC 28‑32. Moderately hard, very easy to machine, low tool wear.
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718H: Adds about 1% nickel (Ni) to the P20 base. Nickel significantly improves hardenability and toughness, raising delivery hardness to HRC 33‑38.
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Impact: 718H is harder and more wear‑resistant than P20, though still easy to machine.
2. Polishability and Surface Quality
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P20: Good polishability, meets requirements of most ordinary plastic products (e.g., inner side of appliance housings, internal structural parts). However, large‑area mirror polishing may produce tiny pits or orange peel.
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718H: Vacuum melting gives higher purity and more uniform microstructure. It polishes easily to #6000‑#8000 grit or higher, ideal for high‑appearance parts like automotive interiors and high‑gloss appliance panels.
3. Dimensional Stability and Deformation Resistance
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P20: Stable for small‑to‑medium molds. For large molds (e.g., bumpers, large TV housings), hardness may vary from surface to core, leading to slight deformation after machining/heat treatment.
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718H: Nickel provides excellent hardenability, ensuring uniform hardness even in large sections.
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Impact: For large molds, 718H has lower deformation risk and higher dimensional accuracy.
4. Application Scenarios and Lifespan
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P20 (Economical choice)
Suitable for: orders requiring 100k‑300k shots; ordinary plastics (PP, PE, ABS); daily goods, toys, ordinary housings with low gloss requirements.
Advantages: low cost, fast machining. -
718H (Performance choice)
Suitable for: 300k‑500k+ shots; glass‑fiber reinforced plastics (high wear resistance); precision molds requiring mirror polish or texture; large, complex molds.
Advantages: longer life, less maintenance, superior surface quality.
III. Material Selection Advice
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If you are making one‑off or short‑run molds, or the product is an internal structural part (not visible), choose P20 – it’s the most cost‑effective.
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If you are making export molds, automotive molds, products requiring high‑gloss, flawless appearance, or glass‑fiber reinforced plastics, you must choose 718H; otherwise, later repair costs will far exceed the material price difference.
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