Effects of austenite reversion during overageing on the mechanical properties of 18 Ni (350) maraging steel

The sequence of austenite reversion during overageing in 18 Ni (350) maraging steel was examined and its effects on the mechanical properties were evaluated. Austenite with different morphological features were identified at different stages of overageing. The reverted austenite caused decrease in the yield strength (YS) and ultimate tensile strength (UTS) and increase in the tensile ductility. Though the presence of austenite appeared to be beneficial to impact toughness in the initial stages of overageing, severe embrittlement was noticed in samples subjected to prolonged ageing. The observed deterioration in toughness with continued overageing was associated with the coarsening of intermetallic precipitates formed during the early stages of ageing. Electron probe micro analysis (EPMA) carried out on fracture surface identified the embrittling species as precipitates rich in titanium and nickel.