Steel Grades for Injection Molds
The selection of steel for injection molds primarily depends on the plastic type, production volume, and surface quality requirements.
Below are the most commonly used steel grades for injection molds, along with their hardness, characteristics, and suitable applications:
| Steel Grade | HRC | Key Features | Application |
| P20 (3Cr2Mo) | 28-36 | Pre-hardened steel, offering good machinability, economical pricing, and moderate wear resistance. | Suitable for small to medium-volume production (approximately 100,000 to 300,000 shots) of common plastics such as ABS, PP, and PE, including applications like appliance housings, toys, and daily necessities. |
| 718H (3Cr2NiMo) | 35-41 | An improved upgrade of P20, this alloy incorporates nickel for enhanced hardness uniformity, superior polishability, and greater toughness compared to P2. | Suitable for molds with high demands and long service life (approximately 300,000 to 500,000 shots), such as automotive Interior components, home appliance parts, and engineering plastics reinforced with glass fiber (e.g., PA, PC/ABS). |
| NAK80 | 37-43 | Pre-hardened mirror-finish steel with exceptional polishing performance (achieving grits up to #10000 and beyond), delivering excellent surface quality after electrical discharge machining. | Suitable for high-gloss or transparent plastic products (such as PC, PMMA), including optical lenses, automotive lamp covers, high-gloss exterior components, etc. |
| S136 (4Cr13) | 48-52 (After Heat treatment) | High-chromium stainless steel offers exceptional corrosion resistance and rust prevention, with excellent polishability. | Suitable for molds used in the production of corrosive plastics (such as PVC and flame-retardant plastics), as well as products requiring high cleanliness standards in medical, food, and other industries. |
| H13/2344 (4Cr5MoSiV1) | 48-52 (After Heat treatment) | Hot-work tool steel, featuring high strength at elevated temperatures, excellent resistance to thermal fatigue, and superior toughness. | Suitable for producing high-temperature engineering plastics (such as PEEK, PEI, LCP) or reinforced plastics with high glass fiber content, commonly used for long-life, high-stress mold inserts. |
When making specific selections, consider the following principles:
By plastic type:
- Standard plastics (e.g., ABS, PP): P20 or 718H
- Transparent plastics (e.g., PC, PMMA): NAK80 or S136 recommended
- Corrosive plastics (e.g., PVC): Must select stainless steel like S136
- Glass-filled plastics: 718H, H13, or higher wear-resistant steels recommended
By production volume: For small to medium runs (<300,000 cycles), P20 is suitable; for high-volume production (>500,000 cycles) or high-precision requirements, 718H, NAK80, or heat-treated S136/H13 are recommended.
Based on surface finish requirements: For products requiring mirror polishing, NAK80 or S136 are the preferred choices.
Based on mold cost: P20 offers the most economical price and is the entry-level option; 718H provides high cost-effectiveness and the widest application range; NAK80 and S136 are higher-priced and used for specialized requirements.