A new 1.9 GPa maraging stainless steel strengthened by multiple precipitating species

• A new ultra-high strength maraging stainless steel with composition of 13Cr–13Co–4.5Ni–3.5Mo–0.5Ti (at.%) has been designed.
• A tensile strength of 1.9 GPa combined with reasonable ductility (10% of elongation) was achieved after aging treatment.
• The evolution of precipitates during aging was investigated using atom probe tomography (APT).
• The precipitation process of precipitates and their effect on mechanical properties were analyzed.

A new ultra-high strength maraging stainless steel with composition of 13Cr–13Co–4.5Ni–3.5Mo–0.5Ti (at.%) has been developed. It was demonstrated that the ultimate tensile strength of the steel could reach 1.9 GPa with reasonable ductility. This breakthrough was achieved by a combined strengthening of three different species of precipitates. The evolution of precipitates with respect of size, morphology and chemical composition during aging at 500 °C was characterized using atom probe tomography (APT) and transmission electron microscopy (TEM). The precipitates were identified to be η-phase Ni3(Ti, Al) phase, Mo-rich R′ phase and Cr-rich α′ phase, developing out of the precursor clusters, Ni–Ti–Al-rich cluster, Mo-rich cluster and Cr-rich cluster, separately. The segregation of Mo and Cr atoms at the precipitate/matrix interfaces was detected and is considered to impede the coarsening of η-phase. Based on the characterizations, the precipitation process of these phases and their effect on mechanical properties were analyzed.

3-D reconstruction of the atomic positions of Cr (purple points), Mo (red points) and isoconcentration surface for regions containing more than 35 at.% Ni + Ti + Al (blue surfaces) shows the evolution of precipitates during aging process.Figure optionsDownload as PowerPoint slide