Microstructure optimization of austenitic Alloy 800H (Fe-21Cr-32Ni)

Research highlights: → Presented a synergistic effect of TMP on microstructure and resulted properties. → Used AFM to quantitatively analyze geometry and distribution of GB precipitates. → Correlated GB characters with precipitates to interpret their effects on properties. → Provided evidence of coherent precipitates at coherent Σ3 boundaries. - Abstract: The microstructural evolution, specifically of grain boundaries, precipitates, and dislocations in thermomechanically processed (TMP) Alloy 800H samples was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The TMP not only significantly increased the fraction of low-Σ coincidence site lattice boundaries, but also introduced nanoscale precipitates in the matrix and altered the distribution of dislocations. Statistical analysis indicates that the morphology and distribution of grain boundary precipitates were dependent on grain boundary types. The microstructure optimization played a synergistic effect on the significantly increased strength with comparable ductility and enhanced intergranular corrosion resistance and creep-fatigue life compared to the as-received samples.