Selection of Tool Steel for High Pressure Die Casting Dies

High-pressure die casting (HPDC) is a high-speed process in which molten metal is injected into a steel die under pressures of 6.9–206.8 MPa (1,000–30,000 psi). The cavity fills and solidifies within seconds, exposing the die surface to repeated thermal and mechanical loading.

During each cycle, the die face undergoes rapid heating upon contact with molten alloy, followed by cooling during part ejection. This creates cyclic compressive and tensile stresses. At the same time, high-velocity metal flow causes surface erosion, while chemical interaction between the molten alloy and the die can result in soldering.

In practice, die life is determined by which failure mechanism dominates under actual operating conditions—thermal fatigue, erosion, or soldering.

Selection Factors

Selecting tool steel for HPDC starts with identifying the dominant failure mode, then matching the material to resist it.

Thermal fatigue (heat checking) is the most common cause of failure. Repeated heating and cooling generate surface cracks that propagate under mechanical stress, eventually leading to spalling or fracture.

To delay this process, the steel must retain strength at elevated temperatures, meaning it must resist temper softening during cyclic heating. At the same time, sufficient toughness is required to slow crack propagation once cracks initiate.

These requirements conflict in practice. Increasing hardness improves resistance to erosion and deformation, but accelerates crack growth. Increasing toughness improves crack resistance but reduces hot strength and wear resistance.

In production, this balance is controlled primarily by selecting hardness within a workable range, rather than by maximizing any single property.

Recommended Tool Steels

Summary Table