PRECIPITATION HARDENING IN 350-GRADE MARAGING-STEEL

Evolution of microstructure in a 350 grade commercial maraging steel h as been examined. In the earlier stages of aging, the strengthening ph ases are formed by the heterogeneous precipitation, and these phases h ave been identified as intermetallic compounds of the Ni3 (Ti, Mo) and Fe2Mo types. The kinetics of precipitation are studied in terms of th e activation energy by carrying out isothermal hardness measurements o f aged material. The mechanical properties in the peak-aged and overag ed conditions were evaluated and the flow behavior examined. The overa ging behavior of the steel has been studied and the formation of auste nite of different morphologies identified. The crystallography of the austenite has been examined in detail. From the microstructural examin ation of peak-aged and deformed samples, it could be inferred that the dislocation-precipitate interaction is by precipitate shearing. Incre ased work hardening of the material in the overaged condition was sugg estive of looping of precipitates by dislocations.