Characteristics of microstructures and mechanical properties of 3 GPa ultrahigh strength maraging steel

Abstract

The miniaturization and lightweight development of aerospace systems have raised higher requirements for the strength and ductility of power shaft materials. In order to develop maraging steel with the strength exceeded 3 GPa，an experimental maraging steel with high contents of Co，Ni，and Mo elements was designed. Its chemical composition is 4Ni-15Co-9Mo-0.86Ti-0.35Al-Fe. Through the high-temperature and large-scale plastic deformation with forging ratio greater than 10，the grains were refined as much as possible. Combining with pre-stretching deformation and cryogenic treatment followed by aging treatment，the tensile strength of the experimental steel reached 3.076 GPa，with the elongation at break of 5.5%，exhibiting excellent strength and plasticity. The analysis and characterization of the microstructures indicated that the lath martensitic microstructure with high dislocation was formed in the experimental steel，and obtained extra fined grains with the average grain diameter of 0.47 μm. TEM and 3DAP results show that a large number of Ni3（Mo，Ti）precipitates is distributed in the matrix，with the average precipitate diameter of 6-7 nm. Precipitation strengthening，grain refinement strengthening and dislocation strengthening are the main strengthening mechanisms，which ensure an ultrahigh strength over 3 GPa of the experimental steel，while the extremely fine submicron grains also ensure the good ductility of the steel.

Keywords

• maraging steel
• 3 gpa ultra-high strength steel
• precipitations
• strengthening mechanisms