Abstract
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, Ni3Ti 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 $$\sqrt m $$ ). 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 Ni3Ti was observed as $$(011)_M //(0001)_{\eta - Ni_3 Ti} $$ and $$(111)_M //(11\bar 20)_{\eta - Ni_3 Ti} $$ . The Orowan mechanism is the dominant strengthening mechanism.
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