Atom probe tomography study of Cu precipitation behavior in 22Cr-13Ni-5Mn austenitic stainless steel

Cu precipitation behavior of a Cr-Ni-Mn austenitic stainless steel containing a small amount of Cu during aging between 923 and 1023 K for up to 24 h was investigated by atom probe tomography with cluster-finding and interfacial segregation analyses. At 923 K, Cu precipitation started at 20 min of aging, forming uniformly dispersed nano-sized precipitates and the number density of precipitates reached the maximum at 2 h of aging, although the volume fraction of precipitates continued to increase with increasing aging time up to 24 h. The precipitate size steadily increased with increasing aging time and temperature. The growth rate of Cu precipitates observed in this study is significantly lower than that in previous studies of other austenitic stainless steels, although the isothermal growth behavior obeys Lifshitz-Slyozov-Wagner theory. It was noted that both Ni and Mn were enriched near precipitate/matrix interfaces, reducing the interfacial energy as a result. This interfacial segregation seems to effectively reduce the growth rate of Cu precipitates during aging, which was significantly lower than that reported for other austenitic steels.