Abstract
Microstructural evolution of modified 2.5Al alumina-forming austenitic steel after isothermal aging at 973 K was investigated by scanning electron microscope (SEM), and X-ray diffraction (XRD). Tensile and vicker's hardness tests were also carried out to study mechanical properties during isothermal aging. The average particle diameter of precipitates was statistically measured and the kinetic model was employed to describe the coarsening of precipitates. The results show that the precipitation sequence of Laves and NiAl phases was related to aging time, and precipitated after 20 h and 100 h in this work, respectively. The average particle diameter of precipitates continuously increased with aging time. And the coarsening rate of the precipitates decreased at 1000 h due to the exhaustion of Nb atoms in matrix. The precipitation of NiAl and Laves phases plays an important role in mechanical properties. The hardness and the work hardening rate continuously increased. In contrast, the elongation gradually decreased. The above results indicated that the effect of aging strengthening. The room-temperature yield strength firstly sluggish increased and then gradually decreased, finally increased significantly due to the increase in σgb, the decrease in σdis and σss, and the change in σppt.
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