The spinodal decomposition in 17-4PH stainless steel subjected to long-term aging at 350 °C

The influence of aging time on the microstructure evolution of 17-4 PH martensitic stainless steel was studied by transmission electron microscopy (TEM). Results showed that the martensite decomposed by a spinodal decomposition mechanism after the alloy was subjected to long-term aging at 350 °C. The fine scale spinodal decomposition of α-ferrite brought about a Cr-enriched bright stripe and a Fe-enriched dark stripe, i.e., αʹ and α phases, separately, which were perpendicular to the grain boundary. The spinodal decomposition started at the grain boundary. Then with prolonged aging time, the decomposition microstructure expanded from the grain boundary to interior. The wavelength of the spinodally decomposed microstructure changed little with extended aging time.