The　15–5　PH　stainless　steel　was　aged　at　500　°C　for　128　h　after　solution　treatment　at　1040　°C　for　1　h.　The　microstructure　and　composition　of　each　phase　in　the　alloy　were　characterized　by　using　transmission　electron　microscopy　(TEM)　and　atom　probe　tomography　(APT).　It　was　found　that　martensite,　retained　austenite　and　reverted　austenite　contained　Cu-rich　precipitates　and　coexisted　in　the　alloy.　These　precipitates　possess　face-centered　cubic　(fcc)　structure　and　orientation　relationships　with　the　matrix　as　following:　[113]M//[112]A//[011]Cu　and　(111¯)Cu//11¯0)M//(111¯)A.　But　the　morphology,　size　and　number　density　of　the　precipitates　in　the　three　phases　are　different.　In　the　martensite,　the　Cu-rich　precipitates　are　coarse,　in　rod-like　shape,　up　to　~40　nm　in　length;　while　in　the　retained　austenite,　they　are　small　spherical　with　an　average　radius　of　~0.8　nm,　and　coherent　with　the　matrix.　In　the　reverted　austenite,　the　precipitates　are　large　and　spheroidal　with　an　average　radius　of　~2　nm,　larger　than　the　size　in　the　martensite　but　smaller　than　that　in　the　retained　austenite,　which　could　be　due　to　the　faster　growing　of　precipitates　in　martensite　than　in　austenite.　©　2022　Elsevier　Inc.