Study on Microstructure Transformation of 17-4PH Stainless Steel after Long-Term Aging at 350℃

The transformation of microstructure with the extension of aging time on the type of 17-4PHstainless steel at 350℃ was studied in this paper by X-ray diffraction and transmission electron microscope. The results showed that there was the matrix of lath martensite and the nano-metric precipitates of ε-Cu and secondary carbide, M₂₃C₆, after the type alloy subjected to solution treatment and temper treatment. When the alloy aged at 350℃ for about 4200 h, the α-α’ spinodal decomposition occurred along the grain boundary and some reversed austenite was transformed. With the age time extended to 11000 h, the spinodal decomposition and G-phase, which consisted of complex nickel silicide, precipitation occurred in matrix at this intermediate temperature. Some sigma phase was also observed.