Evolution Mechanism of Mo-Rich, B2-NiAl, and Cu-Rich Particles under High Temperature and Its Influence on Thermal Stability and Thermal Fatigue in a Maraging Hot Work Steel SDH88

Abstract

A novel maraging hot work steel designed for integrated die casting, SDH88 (10Cr5Mo4Ni4AlCu), is developed. The traditional Cr-Mo-V hot work steel is commonly used in high-pressure die casting due to both excellent strength and toughness. However, they show unsatisfactory tempering resistance (TR) at temperatures above 600 °C, which may not meet the demands of integrated die-casting technology. Compared with H11 steel, which is primarily used in integrated die casting, SDH88 demonstrates superior hardenability and improved TR. For SDH88 steel, the TR mechanism is influenced by precipitation strengthening (${\sigma }_P$) and dislocation strengthening (${\sigma }_{\text{Dis}}$). The results of thermal fatigue tests show that the SDH88 exhibits better thermal fatigue resistance than that of H11. The crack propagation mechanism is transgranular. The new DRXed grain formed near the thermal crack with random orientation acts as a barrier to the thermal crack propagation. Finally, this work demonstrates that the new alloy composition design allows the application of maraging steels in die-casting steels with advantages in obtaining better TR and thermal fatigue resistance and potential for industrial production. A new approach for designing hot work die steel without quenching treatment during mold processing is proposed.