The characterization of G-phase in Fe20Cr9Ni cast duplex stainless steel

Highlights: • A new morphology of G-phase with a cubic morphology was found in a Z3CN20.09 M duplex stainless steel. • The intensity of (400)_G spot decreases and disappears with the prolongation of the thermal aging time. • The transition of super structure occurred in the G-phase due to the rearrangement of elements in G-phase. -- Abstract: The G-phase with a cubic morphology in a Fe20Cr9Ni duplex stainless steel was found after thermally aged at 475 °C for different times in this study. The microstructural evolution, crystal structure and composition distribution of the G-phase were studied by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) in this study. The experimental results showed that the morphology of the G-phase was mainly controlled by the misfit degree between the matrix and the G-phase. Moreover, the growth of G-phase was confirmed to be in accord with the Ostwald ripening mechanism. During its growth, the Cr element in the matrix partly replaced the Si and Mn elements in the G-phase, resulting in a change in the intensity of the (400)_G spot of the G-phase. With the extension of thermal aging time and the growth of G-phase, the original periodic of the G-phase was destroyed and the super structural change took place in this duplex stainless steel.