Common materials for die casting molds
The material selection for die-casting molds requires comprehensive consideration of the operating conditions, stress conditions, and performance requirements of each mold component. Different materials are used for different parts due to their varying functions to maximize cost-effectiveness. Core components, as they come into direct contact with the hot molten metal, are a key focus in material selection. Currently, the most widely used steel is H13 steel (4Cr5MoSiV1), a hot-work die steel with excellent thermal strength, wear resistance, and thermal fatigue resistance, maintaining high hardness and strength below 600°C. After quenching (1020-1050°C oil cooling) and double tempering (550-580°C), H13 steel can achieve a hardness of HRC45-50, a tensile strength ≥1200 MPa, and an impact toughness αk ≥25 J/cm². This steel effectively resists thermal shock and wear during aluminum alloy die-casting, making it suitable for the cavities and cores of medium- and large-scale mass-produced die-casting molds, such as automotive engine blocks and transmission housings.
Depending on the die-casting material and production batch size, other specialized materials can be selected for molded parts. 3Cr2W8V steel is a traditional hot-work die steel with superior heat resistance to H13 steel. It maintains high strength at 650°C, making it suitable for die-casting molds for high-melting-point materials such as copper alloys and magnesium alloys. However, its toughness and thermal fatigue resistance are slightly inferior to H13 steel. After quenching (1050-1100°C) and tempering (600-650°C), it has a hardness of HRC40-45, making it suitable for small-batch, high-temperature die-casting scenarios. 718H pre-hardened steel is a pre-hardened plastic mold steel that can also be used for zinc alloy die-casting molds with lower requirements. Its factory hardness reaches HRC32-36, eliminating the need for subsequent heat treatment and reducing machining deformation. It is suitable for small die-casting molds with complex shapes and high precision requirements, such as cavity inserts for electronic connector molds. In addition, for die-casting molds with extremely large batches (over 1 million pieces), powder metallurgy high-speed steel (such as ASP-60) can be used. Its wear resistance and thermal fatigue resistance far exceed those of ordinary mold steel, but its cost is relatively high and it is only used in high value-added products.
Structural components (such as formwork, base plates, and bearing plates) primarily serve the purpose of load bearing and support. Material selection prioritizes strength, rigidity, and cost-effectiveness. 45 steel is the most widely used structural steel, offering low cost and excellent processability. After quenching and tempering (840-860°C quenching and 550-600°C tempering), it achieves a hardness of HB220-250 and a tensile strength of 600-800 MPa, making it suitable for formwork and base plates in small and medium-sized molds. S50C steel (high-quality carbon structural steel) offers slightly better performance than 45 steel, with a higher carbon content (0.47%-0.55%). After quenching and tempering, it achieves a hardness of HB240-280 and a tensile strength of ≥650 MPa, making it suitable for medium-sized formwork subjected to high loads, such as the movable formwork in automotive wheel die-casting molds. For large molds (weighing more than 5 tons), QT500-7 ductile iron is a better choice. It has excellent casting performance, can be made into complex shapes, and has good shock absorption and wear resistance. Its tensile strength is ≥500MPa and elongation is ≥7%. It is suitable for large seat plates and support plates, which can reduce processing volume and cost.
Guide parts and ejection parts must balance wear resistance and motion accuracy. SUJ2 (high-carbon chromium bearing steel) is the preferred material for guide parts (guide pins and guide sleeves). It contains approximately 1.0% carbon and 1.5% chromium. After overall quenching (830-860°C oil cooling) + low-temperature tempering (150-200°C), the hardness can reach HRC58-62. It has excellent wear resistance and can be ground to a surface roughness of less than Ra0.1μm, ensuring that the guide clearance is controlled at 0.01-0.03mm. 20CrMnTi steel is a representative of carburizing steel, suitable for large guide pillars and guide keys. After carburizing (900-930℃) + quenching (850-880℃ oil cooling) + low-temperature tempering, the surface hardness reaches HRC58-62 and the core hardness reaches HRC30-40. It has both high surface wear resistance and good core toughness. The carburized layer depth is 0.8-1.2mm, which prevents surface peeling during use.
The material selection for ejector mechanism components (ejector rods, ejector tubes, and return levers) requires a balance between strength and wear resistance. T8A carbon tool steel is suitable for ejector rods. After quenching (760-780°C water quenching) and low-temperature tempering (180-200°C), it achieves a hardness of HRC50-55. It is cost-effective and easy to process, making it suitable for low-melting-point die-casting molds, such as zinc alloys. Cr12MoV steel is a cold-work die steel with excellent wear resistance. After quenching (950-1000°C oil cooling) and low-temperature tempering, it achieves a hardness of HRC58-62. It is suitable for ejector tubes and return levers, especially where precise fit with the core is required, as it can reduce wear-induced clearance increases. For ejector parts operating in high-temperature environments (such as aluminum alloy die-casting molds), H13 steel, with a hardness of HRC45-50, remains the preferred choice. It provides sufficient wear resistance and good thermal fatigue resistance, preventing cracks from repeated hot and cold cycles. Auxiliary parts such as gate sleeves are usually made of H13 or 3Cr2W8V steel, while exhaust inserts are made of powder metallurgy materials to take into account both air permeability and wear resistance. The reasonable combination of these materials constitutes a complete material system for the die-casting mold.
