Abnormal grain growth under solution-aging treatments enables convergence mechanical properties of a Fe-Ni-Cr based austenitic alloy

In this study, systematic heat treatment routes including solution (980 degrees C to 1130 degrees C) and aging (675 degrees C to 775 degrees C) processes were used to tailor the microstructural evolution and mechanical performance of a Fe-Ni-Cr based austenitic alloy, strengthened by a gamma ' phase (Ni-3(Ti, Al)). Grain growth was observed with increasing solution treatment temperature from nearly 90 mu m (980 degrees C) to nearly 200 mu m (1130 degrees C). Grain refinement during solution heat processes was found to ascribe to the solute drag effect and the pinning effect of nickel-titanium-enriched segregates and precipitates. During aging, the precipitation behavior of gamma ' is found to be almost independent of solution treatment temperatures. Interestingly, abnormal grain growth during aging was observed. The motion of grain boundaries was ascribed to the formation of nickel-titanium-enriched gamma ' in the austenitic matrix, thereby contributing to the dissolution of the previously enriched segregates and precipitates from grain boundaries. The studied alloy shows a wide range of mechanical properties, from tensile strength of 1131 MPa with ductility at 36%, to tensile strength of 880 MPa with ductility at 50%. The current study demonstrates that grain refinement of the alloy at solution treatment may not benefit the final mechanical properties.