Mold Steel Selection for PEEK Products

As a high-performance special engineering plastic, PEEK requires an injection temperature of 360–400°C and mold temperature of 180–220°C. It has high melt viscosity and is often reinforced with glass fiber or carbon fiber, imposing strict requirements on mold steel’s high-temperature resistance, wear resistance, corrosion resistance and dimensional stability. Rational mold steel selection directly determines mold service life, molding quality and production stability, requiring systematic matching based on product precision, application environment, production volume and material characteristics.

Core Principles of Mold Steel Selection

Mold steel must exhibit excellent high-temperature stability without softening or deformation under long-term cyclic high-temperature conditions, with good thermal fatigue resistance. The material should achieve high hardness and wear resistance to effectively resist scouring and wear from reinforcing fillers, reducing issues such as flash and dimensional deviation. For corrosive gases that may be produced at high temperatures and special applications such as medical and food contact, mold steel must possess corresponding corrosion resistance. The material should also balance toughness and structural strength to avoid chipping and cracking under high injection pressure, with long-term dimensional stability required for precision products.

Classification and Application of Common Mold Steels

General Heat-Resistant Mold Steels

H13 is a national standard 4Cr5MoSiV1 hot work tool steel with a hardness of HRC48–52 after vacuum heat treatment and a heat-resistant temperature range of 500–600°C. It offers good toughness and thermal fatigue resistance, serving as a conventional material for PEEK molding, suitable for general PEEK products with medium production volume in non-corrosive environments. 8407 and 2344 are improved H13 grades with higher purity and uniform internal structure, achieving HRC50–54 after heat treatment, with superior heat and wear resistance, suitable for mid-to-high-end PEEK products and mass production molds.

Corrosion-Resistant Mold Steels

S136 is a martensitic corrosion-resistant stainless steel with HRC48–52 after heat treatment, excellent polishability for high mirror finish, and outstanding acid and alkali corrosion resistance, suitable for PEEK products requiring high hygiene and corrosion resistance such as medical, food contact and semiconductor applications. 420-series stainless steel provides basic corrosion resistance with HRC48–52 after heat treatment and moderate polishability, suitable for cost-sensitive applications with general corrosion requirements.

High-Wear-Resistance and High-Toughness Mold Steels

8503 is a low-silicon high-molybdenum alloy mold steel without carbide segregation, achieving HRC55–60 after heat treatment, with outstanding anti-sticking, chipping resistance and wear resistance, suitable for high-proportion glass fiber and carbon fiber reinforced PEEK materials and complex structures prone to wear. LG mold steel achieves HRC54–58 while maintaining excellent toughness, effectively preventing cavity collapse and flash in thin-wall, sharp-corner and high-injection-pressure PEEK applications.

Pre-Hardened Precision Mold Steels

NAK80 is a pre-hardened mirror mold steel with factory hardness HRC40–42, requiring no subsequent heat treatment, with excellent machinability and dimensional stability and high mirror polishability, suitable for small-to-medium batch precision PEEK products with tight delivery schedules.

Heat Treatment and Surface Treatment Requirements

PEEK mold steel is recommended for vacuum heat treatment to avoid oxidation and decarburization, with standardized quenching and tempering to ensure uniform structure. Large molds may add cryogenic treatment to further enhance dimensional stability. For severe wear conditions such as glass fiber reinforcement, nitriding can be applied to improve surface hardness and wear resistance. For high-wear-resistance and low-friction applications, composite treatments such as PVD coating can significantly extend mold life. For molds requiring high corrosion resistance and finish, hard chrome plating can be used to improve demolding performance and corrosion resistance.

Structural Design and Supporting Material Requirements

Core and cavity components must select corresponding mold steels based on working conditions, while non-molding components such as mold bases can use standard mold steels such as P20 and 718H to control costs while ensuring performance. PEEK’s high-temperature molding characteristics require rational cooling system design and stable temperature control. Hot runner systems must meet high-temperature resistance above 400°C to ensure stable melt flow. Moving components such as ejection and guiding parts should use high-temperature-resistant, wear-resistant standard parts matching mold steel performance.

Application Precautions

Standard pre-hardened steels such as conventional P20 lack sufficient high-temperature resistance and wear resistance to adapt to PEEK’s high-temperature molding environment and are prohibited for key parts such as cores and cavities. Ordinary stainless steel cannot meet the dual corrosion and wear resistance requirements of PEEK molding, requiring dedicated corrosion-resistant mold steel. Molds for high glass fiber and carbon fiber reinforced PEEK must be equipped with corresponding surface treatment to avoid rapid cavity wear. Precision PEEK products should adopt a combination of vacuum heat treatment and cryogenic treatment to reduce deformation and ensure dimensional accuracy.

Conclusion

Mold steel selection for PEEK products focuses on working condition adaptation. General non-corrosive environments can choose general heat-resistant steels such as H13, 8407 and 2344. Corrosion-resistant scenarios such as medical and food applications prioritize corrosion-resistant stainless steels such as S136. High-filler applications select high-wear-resistance and high-toughness steels such as 8503 and LG. Small-batch precision rapid delivery scenarios can use pre-hardened steel such as NAK80. Combined with standardized heat treatment, surface treatment and rational mold structural design, mold service life can be effectively improved, ensuring stable molding quality and production efficiency of PEEK products.