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 degrees 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 alpha'-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 x 1014 m- 2 to 37.8 x 1014 m- 2, resulting in a high strain hardening rate. In contrast, the dislocation density in the unaged MSS increases slightly from 33.4 x 1014 m- 2 to 34.1 x 1014 m- 2.