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How to Choose the Right Steel Material for Plastic Injection Molds
How to Choose the Right Steel Material for Plastic Injection Molds
Selecting the right steel depends primarily on production volume, plastic material (corrosiveness & abrasiveness), and surface finish requirements. At LONGXIANG, we guide clients through three main steel categories: pre-hardened (P20, 718H) for general-purpose molds under 500K cycles, through-hardened (H13, 420SS) for high-volume molds up to 2M cycles, and high-polish steels (S136, NAK80) for optical-grade surfaces.
Steel Comparison Guide
| Steel Grade | Hardness (HRC) | Max Cycles | Best For | Polishability | Corrosion Resistance |
|---|---|---|---|---|---|
| P20 (1.2311) | 28–32 | 500K | General purpose, low-medium volume | Good (SPI B1) | Low |
| 718H | 32–36 | 800K | Larger molds, automotive parts | Good (SPI B1) | Low |
| H13 (1.2344) | 48–52 | 1.5M | High-wear, high-temperature molds | Fair (SPI B2) | Medium |
| 420SS | 48–52 | 2M | Corrosive plastics (PVC, flame-retardant) | Good (SPI A2) | High |
| S136 (1.2083) | 48–52 | 2M | Optical, medical, food-contact parts | Excellent (SPI A1) | High |
| NAK80 | 37–42 | 1M | Texture, mirror finish, lens molds | Excellent (SPI A1) | Medium |
3-Step Selection Framework
1
Define Production Volume
Under 100K cycles → P20 or 718H. 100K–500K → 718H or NAK80. Over 500K → H13 or 420SS. xox recommends 718H as the cost-effective default for most projects.
2
Check Plastic Material Compatibility
PVC, POM, and flame-retardant grades release corrosive gases → use 420SS or S136. Glass-filled nylons are abrasive → use H13 with TiN coating. Standard materials (ABS, PP, PE) work well with P20 or 718H.
3
Determine Surface Requirements
SPI A1 mirror finish → S136 or NAK80. SPI B1 fine texture → 718H or P20. SPI C satin → most steels. Chemical etching → NAK80 for best consistency.
Pro Tips from LONGXIANG Engineers
For molds running ABS or PP under 300K cycles, P20 is the most cost-effective choice with excellent machinability.
Always consider surface coating (TiN, TiAlN, DLC) — it can extend mold life by 2–3x without upgrading the base steel.
At LONGXIANG, a comprehensive DFM analysis includes steel recommendation with lifecycle cost projection — free of charge.
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