PI (Polyimide) is a high-performance engineering plastic with a high molding temperature ranging from 380–430°C, and the corresponding mold temperature also needs to be maintained at 170–210°C. Meanwhile, this material has poor fluidity and releases trace corrosive gases during high-temperature molding, which continuously erodes the mold cavity and core. Based on this, mold steels suitable for PI molding must possess five core properties simultaneously: high temperature resistance, thermal fatigue resistance, high wear resistance, corrosion resistance, and dimensional stability, to maintain mold accuracy and service life during long-term high-temperature production.
1. H13/SKD61/2344 (Improved Hot-Work Mold Steel)This series is the preferred general-purpose material for PI molds. These steels are mainly composed of chromium, molybdenum, and vanadium as alloying elements. After vacuum quenching and cryogenic treatment, their hardness can reach HRC 48–52. They can withstand repeated thermal shocks from high-temperature PI melts and effectively avoid thermal cracks, while also offering excellent wear resistance to reinforcing fillers such as glass fiber and carbon fiber. This makes them ideal for the mass production of most PI products, offering a balanced combination of performance and cost-effectiveness.
2. S136/S136H/2083 (High-Chromium Stainless Steel)For high-purity PI for medical and electronic applications or products requiring mirror-high gloss surfaces, high-chromium stainless steels are the better choice. Their high chromium content provides extreme corrosion resistance, protecting against the erosion of PI decomposition products. They also feature excellent polishability, achieving a mirror-level surface finish. In pre-hardened state, they have a hardness of HRC 35–40, which increases to HRC 50–54 after quenching, ensuring both corrosion resistance and structural strength.
3. 718H/1.2738 (Pre-Hardened High-Quality Plastic Mold Steel)Suitable for small-to-medium batch production of pure PI (unfilled) structural parts with general appearance requirements, this steel is in a pre-hardened state and requires no additional heat treatment. It offers good toughness and ease of machining, enabling rapid molding of complex cavities with a hardness of HRC 33–38. However, its high-temperature resistance and wear resistance are relatively weak, so it is only suitable for short-term, small-batch production and not recommended for high glass fiber-filled or ultra-large-scale production scenarios.
4. 8407/DAC55 (Premium Hot-Work Steel, Upgraded Version of H13)As an upgraded variant of H13, this steel delivers superior thermal cracking resistance and high-temperature strength due to its higher purity and more uniform microstructure. After heat treatment, its hardness reaches HRC 50–54, with excellent dimensional stability. It is designed for high-end precision PI molds operating under ultra-high temperature and high stress conditions, meeting the long-life requirements of high-precision, high value-added PI parts.
5. Powder Metallurgy Steels (Such as ASP23, ASP30)For extreme wear conditions where glass fiber content exceeds 40% and the required mold cycles exceed 1 million, powder metallurgy steels are the ultimate choice. These steels achieve uniform carbide distribution through powder metallurgy, with hardness exceeding HRC 60 and wear resistance 2–3 times that of ordinary H13. Despite their high cost and difficult processing, they are suitable for the mass production of high value-added products.
Key Material Selection RecommendationsExcept for pre-hardened steel 718H, steels such as H13 and S136 must undergo vacuum quenching and cryogenic treatment, strictly controlling hardness at HRC 48–52 to avoid deformation and cracking at high temperatures. Additionally, PI molds are recommended to be treated with nitriding (HV 900–1100) or PVD coating (TiN, TiCN) to further improve wear resistance, corrosion resistance, and demolding performance. It is crucial to avoid ordinary steels like P20 and 45# steel, as their poor heat resistance leads to rapid softening, wear, and rusting under PI's high-temperature environment, resulting in premature mold failure and increased costs.
