Heterogeneous nucleation of Ni3Ti by Mo-enriched particles enhances strength and fracture toughness of maraging steel

Developing ultra-high strength and high toughness maraging steel requires an effective route of a well-designed heat treatment regimen to control the precipitates. In this study, we regulated the heterogeneous nucleation sites through Mo-enriched particles to increase the nucleation rate of Ni 3 Ti. The Mo-enriched particles as Ni 3 Ti precursors decrease the lattice mismatch between α-Fe and Ni 3 Ti, reducing crack formation at the interface. We tailored the maraging steel utilizing duplex aging treatment (DAT) to break the conventional precipitation pathway. The DAT comprises a solid solution treatment followed by a two-step aging treatment at 370 °C and 480 °C. The Mo-enriched particles precipitated after solid solution treatment due to the low solubility and diffusion rate at low temperatures. The aging treatment conducted at 370 °C enhances the density of the Mo-enriched particles and inhibits the formation of Ni 3 Ti. The pre-formed precipitates act as heterogeneous nucleation sites for Ni 3 Ti during aging at 480 °C, increasing the nucleation rate and reducing the size. As aging continues, Mo segregates to the interface of Ni 3 Ti and the matrix, inhibiting the growth of Ni 3 Ti and forming Fe 7 Mo 2 precipitates. The DAT steel exhibits an excellent yield strength of 2093 MPa and fracture toughness of 77 MPa∙m 1/2 at room temperature. The well-regulated precipitates increase crack nucleation energy, forming a curved primary crack and multiple secondary cracks, which reduce stress concentrations and increase fracture toughness. The DAT strategy provides a new avenue for improving fracture toughness while maintaining high strength in maraging steel. • Regulating the heterogeneous nucleation sites through Mo-enriched particles increases the nucleation rate of Ni 3 Ti and reduces the size of the precipitates. • The conventional precipitation pathway was broken using duplex aging treatment to overcome the significant decrease in fracture toughness. • The well-regulated precipitates increase crack nucleation energy, forming a curved primary crack and multiple secondary cracks.