Selection of Tool Steel for Low-Pressure Die Casting Dies
Low-pressure die casting (LPDC) is a controlled bottom-filling process in which molten metal is pushed into the die cavity by gas pressure. The stable filling behavior reduces turbulence and porosity, but does not reduce the thermal and chemical load on the die.
LPDC dies operate under cyclic heating and cooling. Contact with molten aluminum or magnesium rapidly raises the surface temperature, followed by cooling during solidification and part ejection. This repeated cycle leads to thermal fatigue (heat checking). At the same time, continuous metal flow causes surface erosion and chemical interaction, such as soldering, especially in aluminum alloys.
Selection Factors
Selection focuses on resistance to thermal fatigue, crack propagation, softening, and heat transfer under cyclic conditions.
Thermal Fatigue Resistance (Heat Checking)
Thermal fatigue is the primary failure mode in LPDC dies. It is driven by repeated temperature changes rather than peak temperature alone. The steel must resist crack initiation and slow crack growth under cyclic stress. This requires stable strength and toughness at operating temperature.
Toughness and Wear Resistance Balance
Increasing hardness improves resistance to erosion and metal flow, but reduces fracture resistance. In LPDC dies, failure often occurs by cracking rather than uniform wear. Dies with sharp corners, thin sections, or stress concentration require higher toughness. Simpler geometries and large contact surfaces can prioritize wear resistance.
Hot Hardness (Tempering Resistance)
Repeated thermal exposure can reduce the hardness in steel that lacks tempering resistance. Loss of hardness leads to plastic deformation, dimensional instability, and accelerated surface damage. The material must maintain hardness under cyclic heating.
Thermal Conductivity
Thermal conductivity affects internal temperature gradients. Higher conductivity reduces thermal stress and slows the formation of heat-checking cracks, especially in water-cooled dies.
Recommended Tool Steels
H13 Tool Steel Supplier | 1.2344 | SKD61
H13 is the standard material for LPDC dies due to its balanced resistance to heat checking, softening, and cracking. It maintains mechanical stability under repeated thermal cycles and provides sufficient toughness to limit crack propagation. A working hardness of 44–48 HRC is typically used to balance durability and crack resistance.
AISI H11 Tool Steel | 1.2343 | SKD6
H11 provides higher toughness than H13, making it more suitable for dies prone to cracking. It is preferred for large dies, complex geometries, or areas with stress concentration. The lower vanadium content improves fracture resistance while maintaining adequate thermal fatigue performance. Typical working hardness is 44–47 HRC.
AISI H10 Tool Steel | 1.2365 | SKD7
H10 is used when thermal stress is the limiting factor. Its higher thermal conductivity reduces internal temperature gradients and the risk of thermal fatigue. It is suitable for heavily cooled dies or higher thermal load conditions. Compared with H13, it sacrifices some wear resistance for improved heat dissipation.
AISI P20 Tool Steel | 1.2311 | 3Cr2Mo
For lower-temperature alloys such as zinc, P20 is a cost-effective option. It is supplied pre-hardened (~300 HB), allowing direct machining and use without heat treatment. It is suitable for low thermal load and limited production cycles, but not for aluminum or magnesium LPDC with high thermal stress.
Summary Table
| Tool Steel Grade | Typical Hardness | Primary Advantage for LPDC |
| H13 | 44–48 HRC | Balanced resistance to heat checking, softening, and cracking |
| H11 | 44–47 HRC | Higher toughness for crack-sensitive dies |
| H10 | 38–46 HRC | Higher thermal conductivity reduces thermal stress |
| P20 | ~300 HB | Cost-effective for low thermal load applications |