γ-Ni3Nb precipitate in Fe-Ni base alloy

For Fe-Ni alloy involving the metastable gamma ''-Ni3Nb precipitates in the standard chemical composition of Fe-43Ni-15Cr-2W-1Mo-3.8Nb-0.1V-0.1Ti-0.28Al-0.1Zr-0.04C (mass%), hardness measurement and TEM analyses were performed during aging at temperatures 650-750 degrees C up to 200 h after 20% cold-rolling. The hardness increases due to coherent gamma ''-Ni3Nb precipitate, but longer aging induces hardness decrease due to its coarsening and dislocation recovery. Aging at 800 degrees C for 200 h leads to transformation to the stable delta-Ni3Nb. Based on these data, an appropriate aging condition is considered to be at the temperature 700-750 degrees C for 8 h in order to distribute finely intra-granular gamma '' precipitates at the final stage of manufacturing. (C) 2013 Elsevier B.V. All rights reserved.