Microstructure and mechanical properties of a 2000 MPa co-free maraging steel after aging at 753 K

The precipitation kinetics at the aging temperature of 753 K in a 2000 MPa grade Co-free maraging steel (Fe-18.9Ni-4.1Mo-1.9Ti, wt pct) has been studied. Under the peak-aged condition at 753 K, Ni^sub 3^Ti precipitates of moderate size were uniformly distributed in the martensite matrix, leading to optimal combination of strength (2000 MPa of yield strength) and fracture toughness (70 MPa[the square root of]m). The ultra-high strength of the maraging steel subjected to long time aging at 753 K is attributed to the high resistance to coarsening of precipitates. The orientation relationship between martensite and Ni^sub 3^Ti was observed as (011)^sub M^//(0001)^sub [eta]-Ni^sub 3^Ti^ and [111]^sub M^//[1120]^sub [eta]-Ni^sub 3^Ti^. The Orowan mechanism is the dominant strengthening mechanism. [PUBLICATION ABSTRACT]