Die casting dies, also known as molds or tools, are subjected to extreme conditions including rapid cyclic heating (from molten metal injection), high pressure, thermal shock, abrasion (from the melt flow and solid particles), and chemical attack (molten metal adhesion/soldering). Therefore, the selection of die materials is critical for die life, casting quality, and economic efficiency. The primary materials used are specialized hot-work tool steels, chosen for their high tempering resistance, thermal fatigue resistance, toughness, and resistance to heat checking and erosion.
1. Primary Hot-Work Tool Steels
These are the most prevalent materials, typically used for the major die components like cavities, cores, and inserts.
H13 (AISI/UDDEHOLM: H13, DIN: 1.2344, WNr: X40CrMoV5-1):
The Industry Standard. This chromium-molybdenum-vanadium hot-work steel offers an excellent balance of key properties.
Properties: Outstanding thermal fatigue resistance (resistance to heat checking), good toughness at operating temperatures (300-600°C), high tempering resistance (retains hardness), and moderate wear resistance. It has good machinability and polishability in the annealed state.
Applications: The most widely used steel for aluminum, magnesium, and brass die casting dies. Suitable for large, complex cavity inserts, cores, and ejector pins. It is often vacuum degassed and electro-slag remelted (ESR) for superior cleanliness and isotropy in large sections.
H11 (AISI: H11, DIN: 1.2343):
Similar to H13 but with lower vanadium and carbon content.
Properties: Slightly higher toughness and better machinability than H13, but with lower tempering resistance and wear resistance at high temperatures.
Applications: Used for dies requiring very high toughness, often for aluminum casting where extreme thermal shock is a concern, or for structural components of the die (e.g., bolster plates).
H10 (AISI: H10, DIN: 1.2365):
A tungsten-molybdenum alloyed steel.
Properties: Excellent resistance to heat softening (high hot hardness) and good thermal fatigue resistance. It can maintain a harder surface at elevated temperatures compared to H13.
Applications: Often chosen for cores and inserts in zinc and aluminum die casting that are subject to severe erosion or soldering.
H19 (AISI: H19, DIN: 1.2581):
A high-tungsten, high-cobalt steel.
Properties: Exceptional high-temperature strength (hot hardness) and resistance to erosion/wear. However, it has lower toughness and is more susceptible to thermal shock cracking.
Applications: Used for “hot spots” in the die, such as thin core pins, gate areas, and high-wear inserts in aluminum and brass die casting, where resistance to washing/erosion is paramount.
H21 (AISI: H21, DIN: 1.2581 similar):
A traditional tungsten-based hot-work steel.
Properties: Very high hot hardness and good wear resistance, but poor thermal conductivity and thermal shock resistance compared to H13.
Applications: Historically common, now often replaced by H13 for most applications. Still used for certain copper alloy (brass, bronze) die casting components due to its high temperature strength.
2. Specialty and Advanced Materials
For specific challenging applications or to extend die life.
Premium/Enhanced H13 Variants: These are ultra-clean, isotropically processed (e.g., via ESR) versions of standard H13. They offer superior toughness, more consistent properties in all directions, and better polishability, leading to improved resistance to heat checking and longer life for high-stress dies.
Maraging Steels (e.g., 1.2709 / Vascomax 300):
Properties: Ultra-high strength and toughness, excellent machinability in the solution-annealed state, and simple heat treatment (age hardening) with minimal distortion.
Applications: Used for high-integrity ejector pins, core slides in complex dies, and sometimes for entire cavity inserts in very large, high-pressure aluminum dies where resistance to cracking is critical.
Copper-Beryllium Alloys (e.g., CuCo2Be):
Properties: Exceptional thermal conductivity (3-4x that of steel), which helps rapidly dissipate heat from the die surface, reducing cycle times and thermal stress.
Applications: Primarily used as inserts or “thermal pins” in hot spots of aluminum dies (e.g., around gates, in dense core areas) to actively manage local temperature and prevent soldering or overheating.
Tungsten-Based Materials:
Anviloy (e.g., Anviloy 1150 – W-Ni-Cu alloy): Very high thermal conductivity, excellent erosion resistance, and low thermal expansion.
Applications: Used for shot sleeves, nozzles, and intensive units in aluminum and brass casting to resist washout and thermal fatigue.
Coatings and Surface Treatments:
While not bulk materials, surface engineering is crucial. Nitriding (gas, plasma, salt bath) and Physical Vapor Deposition (PVD) coatings like CrN, TiAlN, or AlCrN are universally applied to H13 and similar steels. They dramatically increase surface hardness, reduce soldering (metal adhesion), and improve lubricity and wear resistance, thereby extending die life significantly.
3. Material Selection Key Considerations
Casting Alloy: Zinc (lower temp ~400°C) allows for lower-alloy steels; Aluminum (~650°C) demands H13/H11; Brass/Bronze (~1000°C) requires high-hot-strength steels like H19/H21 or tungsten alloys.
Die Component Function: Cavity/cores need thermal fatigue resistance; Gate areas and runners need erosion resistance; Ejector pins need strength and toughness.
Production Volume: High-volume runs justify premium materials and coatings.
Cost: Balancing initial material and processing cost against total lifetime and maintenance cost.
Summary Table
| Material (AISI) | Key Characteristics | Primary Application in Die Casting |
| H13 | Best all-round: thermal fatigue, toughness, temper resistance | Industry standard for Al/Mg/Zn cavities, cores, inserts. |
| H11 | Higher toughness, lower hot strength vs. H13 | Dies requiring exceptional shock resistance. |
| H10 / H19 | Superior hot hardness & erosion resistance | Cores, pins, gates in Al/brass casting; severe wear areas. |
| Maraging Steel | Ultra-high strength & toughness, minimal distortion | High-stress ejector systems, complex core slides. |
| Copper-Beryllium | Excellent thermal conductivity | Cooling inserts for local hot spot management. |
| Tungsten Alloys | Extreme erosion resist. & thermal conductivity | Shot sleeves, nozzles for Al/brass. |
In conclusion, H13 steel is the versatile workhorse of the die casting industry. The selection, however, is optimized by combining it with specialty materials like copper alloys for cooling, tungsten materials for erosion zones, and premium/coated variants for critical, high-volume production to maximize performance and tool life.
