Effects of nanoprecipitates on mechanical properties in an ultra-high strength maraging stainless steel

A new maraging stainless steel (MSS) with excellent balance of strength and ductility was designed. The ultimate tensile strength (UTS) of the MSS after aging at 500 °C for 100 h reaches 2068 MPa, with a total elongation of 9.3 % and a uniform elongation of 3.1 %. Compared with the unaged MSS, the MSS steel aged for 100 h showed an increase of 783 MPa in UTS, with only a slight reduction in ductility. After aging for 100 h, the sizes of Fe₂Mo, Ni₃Nb, and α’-Cr phases are 21.5 nm, 6.6 nm, and 5.4 nm, respectively. Long time aging for 100 h, Fe₂Mo grows significantly along with a large misfit of 16 % between martensite matrix and Fe₂Mo. Upon deformation, the dislocation density in MSS aged for 100 h increases from 22.9 × 10¹⁴ m⁻² to 37.8 × 10¹⁴ m⁻², resulting in a high strain hardening rate. In contrast, the dislocation density in the unaged MSS increases slightly from 33.4 × 10¹⁴ m⁻² to 34.1 × 10¹⁴ m⁻².