Choosing the right plastic mold steel is crucial for the service life of your molds and the precision of your plastic products. A wrong choice can lead to frequent mold damage, increased production costs, and delayed delivery. In this guide, you will learn the core indicators for selecting plastic mold steel, how to match different plastics with the right steel grades, and how to avoid common selection mistakes—all designed to help you make the best decision for your production needs.
Key Indicators for Plastic Mold Steel Selection
When selecting plastic mold steel, you need to focus on four core indicators to ensure it meets your production requirements:
- Hardness: The hardness of the mold steel directly affects its wear resistance. For general plastic injection molds, the delivery hardness of 28-32 HRC is sufficient; for high-precision or high-wear molds, choose steel with hardness above 35 HRC.
- Polishability: If your plastic products require a high-gloss surface (such as cosmetic packaging, medical devices), choose mold steel with good polishability, such as S136 or NAK80, which can achieve mirror polishing effect.
- Corrosion Resistance: For corrosive plastics (such as PVC, PC, or plastics containing flame retardants), mold steel with strong corrosion resistance is necessary to prevent mold rust and damage. S136 and 2083 are ideal choices.
- Machinability: Good machinability can reduce processing time and costs. P20 and 718H are pre-hardened plastic mold steels with excellent machinability, suitable for mass production.
Mold Steel Selection for Different Plastics
Different plastics have different properties, so the corresponding mold steel grades also vary. The following table summarizes the matching relationship between common plastics and mold steel, which you can directly refer to:
| Plastic Type | Recommended Mold Steel Grade | Core Advantages |
| PVC (Corrosive) | S136, 2083 | Strong corrosion resistance, good polishability |
| PP/ABS (General Plastic) | P20, 718H | Cost-effective, good machinability |
| PC/PMMA (High Transparency) | S136, NAK80 | High polishability, no streaks on product surface |
| Engineering Plastics (PA, POM) | 718H, H13 | High hardness, good wear resistance |
Common Mistakes in Plastic Mold Steel Selection
Many purchasers make mistakes in selection due to insufficient understanding of mold steel, which leads to unnecessary losses. Here are the most common mistakes to avoid:
- Blindly pursuing high hardness: High hardness does not mean better performance. For general plastic molds, excessive hardness will reduce the toughness of the steel, leading to mold cracking.
- Confusing pre-hardened steel with quenched steel: Pre-hardened steel (such as P20, 718H) can be directly processed without heat treatment, while quenched steel (such as S136) needs heat treatment to achieve the required hardness. Choosing the wrong type will increase processing costs.
- Ignoring corrosion resistance for corrosive plastics: Using ordinary mold steel (such as P20) for PVC molds will lead to rapid rust and damage of the mold, reducing the service life of the mold.
If you are still unsure about which plastic mold steel to choose for your specific production needs, we can provide you with a free selection plan. Our plastic mold steel includes P20, 718H, S136 and other mainstream grades, supporting custom cutting and processing. Contact us now to get a free quote and material data sheet!