Key Takeaways (Quick Summary)
- The Core Difference: 718 is essentially P20 + Nickel (Ni). The addition of roughly 1% Nickel improves hardenability and toughness.
- Hardness: P20 is typically 28–32 HRC; 718 (specifically 718H) is typically 33–38 HRC.
- Best Use Case: Use P20 for medium/small molds and structural parts to save costs. Use 718 for large mold bases, high-gloss surfaces, and long-life production requirements.
- Polishing: 718 offers superior polishing results due to its uniform microstructure.
1. Introduction
In plastic injection mold manufacturing, P20 mold steel(1.2311) and 718 mold steel are two of the most commonly used materials.
They are often compared because they share a similar base composition, yet their performance, hardness level, and suitable applications differ significantly.
Choosing the right mold steel directly affects tool life, surface finish, machining cost, and final product quality. This article explains the core differences between P20 and 718, helping engineers and buyers make a more informed decision.
2.What Is P20 Mold Steel?
P20 mold steel is a pre-hardened chromium-molybdenum alloy steel, widely used for general plastic injection molds.
It is typically supplied in a pre-hardened condition with a hardness range of 28–36 HRC, allowing it to be machined directly without additional heat treatment.
2.1 Key Characteristics of P20:
- Good machinability and polishing performance.
- Uniform hardness throughout the section.
- Delivered in pre-hardened condition.
- Cost-effective for standard mold applications.
2.2 Typical Applications:
- General plastic injection molds.
- Medium-sized mold bases.
- Low to medium production volumes.
Learn more about our P20 Mold Steel(1.2311) products.
3. What Is 718 Mold Steel (718H / 1.2738)?
718 mold steel is an upgraded version of P20, enhanced with nickel to improve hardness uniformity, toughness, and polishing performance.
It is commonly known as DIN 1.2738 and is also supplied in a pre-hardened state, typically 33–38 HRC, depending on the specification.
3.1 Key Advantages of 718 Mold Steel:
Higher hardness and better wear resistance than P20.
- Improved toughness due to nickel content.
- Excellent polishing and photo-etching performance.
- More stable internal structure, suitable for large molds.
3.2 Typical Applications:
- Large injection molds.
- High-gloss plastic parts.
- High-volume production molds.
- Precision plastic components.
4.P20 vs 718 Mold Steel: Key Differences
| Feature | P20 Mold Steel | 718 Mold Steel (1.2738) |
| Hardness Range | Cr-Mo alloy | Cr-Mo alloy + Nickel |
| Hardness Range | 28–36 HRC | 33–38 HRC |
| Wear Resistance | Medium | Higher |
| Polishing Ability | Good | Excellent |
| Toughness | Standard | Improved |
| Mold Size Suitability | Small to medium molds | Medium to large molds |
| Cost | Lower | Higher |
Simple conclusion: P20 is economical and versatile, while 718 offers better performance for higher-end mold requirements.
5. Why Is 718 Harder Than P20?
The main reason is the addition of nickel (Ni) in 718 steel. Nickel improves hardenability and toughness, allowing the steel to maintain consistent hardness from surface to core, especially in large mold blocks.
6. Is 718 Always Better Than P20?
Not necessarily. The choice depends on the application:
- Choose P20 if: Mold surface finish requirements are moderate.
- Production volume is limited.
- Cost control is a priority.
- Choose 718 if: High surface quality is required.
- Mold size is large.
- Long mold life and stability are critical.
7. Can P20 or 718 Be Used for Special Plastics?
For most standard plastic materials, both steels perform well.
However, for high-corrosion or ultra-high polish requirements, steels like S136 or NAK80 may be more suitable.
Q: Can I weld P20 and 718? A: Yes, both can be welded, but pre-heating is required to prevent cracking. Since 718 has Nickel, check for compatible welding rods to match the hardness.
Q: Is 718H different from 718? A: Usually, "H" stands for Hard. Standard 718 might be ~30 HRC, while 718H is heat-treated to 34-38 HRC. Always specify the hardness range when ordering.
Q: Are there better options than 718? A: Yes. For corrosive plastics (PVC), use Stainless Steel (1.2083/S136). For ultra-high mirror polishing, use NAK80.
8. Conclusion
- Think of P20 as the "Economic Standard" and 718 as the "Performance Standard."
- Use P20 to save costs on structural parts and standard molds.
- Upgrade to 718 for cavity/core inserts where surface finish, hardness depth, and longevity are critical.